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1 A. Császár, L. Jicsinszky, T. Turányi
Generation
of model reactions leading to limit cycle behaviour
React.Kinet.Catal.Lett.,
18, 65-71(1981)
ABSTRACT
2 A. Császár, P. Érdi, L. Jicsinszky, T.
Tóth, T. Turányi
Several
exact results on deterministic exotic kinetics
Z.
Phys.
Chem. (Leipzig), 264, 449-463(1983)
ABSTRACT
3 S. Vajda, P. Valkó, T. Turányi
Principal
component analysis of kinetic models
Int.J.Chem.Kinet., 17,
55-81(1985)
ABSTRACT
4 S. Vajda, T. Turányi
Principal
component analysis for reducing the Edelson-Field-Noyes model of the
Belousov-Zhabotinsky reaction
J.Phys.Chem., 90,
1664-1670(1986)
ABSTRACT
5 T. Bérces, T. Turányi, L. Haszpra
The
kinetics of reactions occuring in the unpolluted troposphere I ,
Formulation of reaction mechanism
Acta Chim.Hung., 122,
147-161(1986)
ABSTRACT
6 L. Haszpra, T. Turányi
Production
of nitric acid in the atmosphere under different conditions
Időjárás, 90,
332-338(1986)
ABSTRACT
7 T. Turányi, L. Haszpra, T. Bérces
A
photochemical air pollution model
Proceedings of the European
Congress on Simulation
Academia , Prague , 1987 ,
Appendix pp 204-207
ABSTRACT
8 T. Turányi, T. Bérces, J. Tóth
The
method of quasi-stationary sensitivity analysis
J.Math.Chem., 2,
401-410(1988)
ABSTRACT
9 L. Haszpra, I. Szilágyi, Gy. Bácskai, T.
Cziczó, A. Demeter, M. Kertész, T. Turányi
Exploratory
measurements
in Budapest for the detection of photochemical air pollution (in
Hungarian)
Egészségtudomány, 32,
363-374(1988)
ABSTRACT
10 T. Turányi, T. Bérces, S. Vajda
Reaction
rate analysis of complex kinetics systems
Int.J.Chem.Kinet., 21,
83-99(1989)
ABSTRACT
11 T. Turányi, T. Bérces
The
kinetics of reactions occuring in the unpolluted troposphere, II .
Sensitivity analysis
React.Kinet.Catal.Lett.,
41, 103-108(1990)
ABSTRACT
12 T. Turányi
Rate
sensitivity analysis of a model of the Briggs-Rauscher reaction
React.Kinet.Catal.Lett.,
45, 235-241(1991)
ABSTRACT
13 T. Turányi
KINAL:
A program package for kinetic analysis of complex reaction mechanisms
Comp.Chem., 14,
253-254(1990)
ABSTRACT
14 T. Turányi
Reduction
of large reaction mechanisms
New J.Chem., 14,
795-803(1990)
ABSTRACT
15 T. Turányi
Sensitivity
analysis of complex kinetic systems: Tools and applications
J.Math.Chem., 5,
203-248(1990)
ABSTRACT
16 L. Györgyi, T. Turányi, R.J. Field
Mechanistic
details of the oscillatory Belousov-Zhabotinskii reaction
J.Phys.Chem., 94,
7162-7170(1990)
ABSTRACT
17 T. Turányi, L. Györgyi, R.J. Field
Analysis
and simplification of the GTF model of the Belousov-Zhabotinsky reaction
J.Phys.Chem, 97,
1931-1941(1993)
ABSTRACT
18 S. Dóbé, T. Turányi, T. Bérces, F. Márta
The
kinetics of hydroxyl radical reactions with cyclopropane and cyclobutane
Proc.Indian
Acad.Sci.(Chem.Sci.), 103, 499-503(1991)
ABSTRACT
19 L. Haszpra, I. Szilágyi, A. Demeter, T. Turányi, T.
Bérces
Non-methane
hydrocarbon and aldehyde measurements in Budapest, Hungary
Atm.Environm., 25A,
2103-2110(1991)
ABSTRACT
20 T. Bérces, T. Turányi
Generation
and distribution of ozone in the vicinity of large pollution
sources (in Hungarian)
Időjárás, 95,
110-118(1991)
ABSTRACT
21 A.S. Tomlin, M.J. Pilling, T. Turányi, J.H. Merkin,
J. Brindley
Mechanism
reduction for the oscillatory oxidation of hydrogen sensitivity and
quasi-steady state analyses
Combust.Flame, 91,
107-130(1992)
ABSTRACT
22 K.J. Hughes, P.A. Halford-Maw, P.D. Lightfoot, T.
Turányi, M.J. Pilling
Direct
measurements of the neopentyl peroxy-hydroperoxy radical
isomerisation over the temperature range 660-750 K
Proc.Combust.Inst, 24,
645-652(1992)
ABSTRACT
23 T. Turányi, A.S. Tomlin, M.J. Pilling
On
the error of the quasi-steady-state approximation
J.Phys.Chem., 97,
163-172(1993)
ABSTRACT
24 S. Dóbé, T. Turányi, I. Iogansen, T. Bérces
Rate
constants of the reactions of OH radicals with cyclopropane and
cyclobutane
Int.J.Chem.Kinet., 24,
191-198(1992)
ABSTRACT
25 T. Turányi
Computational
investigation
of the kinetics of reaction systems (in Hungarian)
Kemiai kozlemenyek, 75,
97-110(1992)
ABSTRACT
26 T. Bérces, T. Turányi
Role
of chemistry in the characterization and depletion of air pollution (in
Hungarian)
Kemiai kozlemenyek, 75,
7-16(1992)
27 T. Turányi, J. Tóth
Comments
to an article of Frank-Kamenetskii on the Quasi Steady State
Approximation
Acta Chim.Hung., 129,
903-914(1992)
ABSTRACT
28 I.Börger, A.Merkel, J.Lachmann, H.-J.Spangenberg,
T.Turányi
An
extended kinetic model and its reduction by sensitivity analysis
for the methanol/oxygen gas-phase thermolysis
Acta Chim. Hung., 129,
855-864(1992)
ABSTRACT
29 T. Turányi, L. Györgyi
Investigation
of complex reaction mechanisms by sensitivity analysis
pp. 298-320 (in Hungarian)
in: Non-linear dynamics and
exotic kinetic phenomena in
chemical systems ( Ed.
Gy. Bazsa)
Debrecen-Budapest-Godollo, 1992
30 L. Zalotai, T. Turányi, T. Bérces, F. Márta
Collisional
energy transfer in the two channel decomposition
of 1,1,2,2-tetrafluorocyclobutane and
1-methyl-2,2,3,3-tetrafluorocyclobutane I. Gas/gas collisions
Reac.Kinet.Catal.Lett.,
51, 401-408(1993)
ABSTRACT
31 L. Zalotai, T. Turányi, T. Bérces, F. Márta
Collisional
energy transfer in the two channel decomposition
of 1,1,2,2-tetrafluorocyclobutane and
1-methyl-2,2,3,3-tetrafluorocyclobutane II. Gas/wall collisions
Reac.Kinet.Catal.Lett.,
51, 409-414(1993)
ABSTRACT
32 S. Dóbé, T. Bérces, I. Szilágyi, T. Turányi, F.
Márta
Kinetic
investigations on oxygen-containing free radicals
Magyar Kem.Lapja, 48,
361-368(1993) (in Hungarian)
33 T. Turányi
Parameterization
of
reaction mechanisms using orthonormal polynomials
Computers Chem., 18,
45-54(1994)
ABSTRACT
34 T. Turányi
Application
of repro-modelling for the reduction of combustion mechanisms
Proc.Combust.Inst., 25,
949-955(1995)
ABSTRACT
35 A.S. Tomlin, T. Turányi, M.J. Pilling
Mathematical
tools
for the construction, investigation and reduction of combustion
mechanisms
in: `Low temperature combustion
and autoignition', eds. M.J. Pilling and G. Hancock,
Comprehensive
Chemical Kinetics, 35,
293–437(1997)
ABSTRACT
36 F.C. Christo, A.R. Masri, E.M. Nebot, T. Turányi
Utilising
artifical neural network and repro-modelling in turbulent combustion
Proceedings of the IEEE
International Conference
on Neural Networks,
Perth, 27th November-1st December 1995,
Vol. 1, pp. 911-916, 1995
ABSTRACT
37 T. Turányi
Applications
of sensitivity analysis to combustion chemistry
Proceedings of SAMO '95 (Theory
and applications of
sensitivity analysis of model
output in computer simulation),
25-27 September, 1995,
Belgirate, Italy, pp. 33-35
38 S. Dóbé, T. Bérces, T. Turányi, F. Márta, J.
Grüssdorf, F. Temps, H.Gg. Wagner
Direct
kinetic studies of the reactions Br+CH3OH and CH2OH+HBr: The heat of
formation of CH2OH
J.Phys.Chem, 100,
19864-19873(1996)
ABSTRACT
39 T. Turányi
Applications
of sensitivity analysis to combustion chemistry
Reliability Engineering
& System Safety, 57, 41-48(1997)
ABSTRACT
40 T. Turányi
Reduction
of reaction mechanisms on the basis of the repro-modelling approach
in: Proceedings of the workshop
on 'Numerical aspects of reduction in chemical kinetics'
2nd September, 1997, CERMICS,
Paris
41 L.J. Clifford, A.M. Milne, T. Turányi, D. Boulton
An
induction parameter model for shock-induced hydrogen combustion
simulations
Combustion and Flame, 113,
106-118(1998)
ABSTRACT
42 T. Turányi, H. Rabitz
Local
methods
pp. 81-99, in: 'Sensitivity
analysis'
eds: A. Saltelli, K. Chan, E.M.
Scott
Wiley, Chichester, 2000
FURTHER
INFO
43 A. Obieglo, J. Gass, A. Büki, T. Turányi
PDF-Berechnung
einer turbulenten Flamme unter Verwendung des Repromodellierens
VDI Berichte, 1492,
487-492(1999)
ABSTRACT
44 T. Turányi
A
reakciókinetika néhány újabb eredménye a légkörkémiában és az
égéstudományban
(Some new results of reaction
kinetics in atmospheric and combustion chemistry)
Magy. Kém. Folyóirat, 55,
323-326(2000)
ABSTRACT
45 K.J. Hughes, T. Turányi, A. Clague, M.J.Pilling
Development
and testing of a comprehensive chemical mechanism for the oxidation of
methane
Int.J.Chem.Kinet., 33,
513-538(2001)
ABSTRACT
46 K.J. Hughes, A.S. Tomlin, E. Hampartsoumian, W.
Nimmo, I.G. Zsély, M.Ujvári,
T. Turányi, A.R. Clague, M.J.
Pilling
An
Investigation of Important Gas Phase Reactions of Nitrogen Species from
the
Simulation
of Bulk Experimental Data in Combustion Systems
Combust.Flame, 124,
573-589(2001)
ABSTRACT
47 T. Turányi, T. Perger and L. Balázs
Reaction-diffusion
modelling
of cylindrical halogen lamps
in: High Temperature
Materials Chemistry
Proceedings of the 10th
International IUPAC Conference
held from 10 to 14 April 2000
at the Forschungszentrum Jülich, Germany
Editors: K. Hilpert, F.W.
Froben and L. Singheiser
Schriften des Forschungszentrum
Jülich, Vol. 15, Part I, pp. 321-324, 2000
ABSTRACT
48 I. Lagzi, A.S. Tomlin, T. Turányi, L. Haszpra, R.
Mészáros, M. Berzins
Modelling
Photochemical Air Pollution in Hungary Using an Adaptive Grid Model
pp. 264-273 in:'Air
Pollution Modelling and Simulation', editor: B. Sportisse,
Springer, Berlin, 2002, ISBN
3-540-42515-2
ABSTRACT
49 I. Lagzi, A.S. Tomlin, T. Turányi, L. Haszpra, R.
Mészáros, M. Berzins
The
Simulation of Photochemical Smog Episodes in Hungary and Central Europe
Using Adaptive Gridding Models.
Lecture Notes in Computer
Science, 2074, 67-76(2001)
ABSTRACT
50 I.Gy. Zsély, T. Turányi
Investigation
and reduction of two methane combustion mechanisms
Archivum Combustionis,
21, 173-177(2001)
ABSTRACT
51 T. Turányi, L. Zalotai, S. Dóbé, T. Bérces
Effect
of the uncertainty of kinetic and thermodynamic data on methane flame
simulation results
Phys.Chem.Chem.Phys., 4,
2568-2578(2002)
ABSTRACT
FULL
TEXT
52 A. Büki, T. Perger, T. Turányi, U. Maas
Repro-modelling
Based
Generation of Intrinsic Low-dimensional Manifolds
J.Math.Chem., 31,
345-362(2002)
ABSTRACT
53 I. Lagzi, A.S. Tomlin, T. Turányi, L. Haszpra, R.
Mészáros, M. Berzins
Modelling
Tropospheric Ozone Formation in Hungary using an Adaptive Gridding
Method
Proceedings from the
EUROTRAC-2 Symposium 2002, P.M. Midgley, M. Reuters (Eds.),
Margraf Verlag, Weikersheim,
2002
ABSTRACT
54 T. Perger, T. Kovács, T. Turányi, C. Trevińo
Determination
of adsorption and desorption parameters from ignition temperature
measurements
in
catalytic combustion systems
J.Phys.Chem. B, 107,
2262-2274(2003)
ABSTRACT
55 I. Gy. Zsély, J. Zádor, T. Turányi
Similarity
of sensitivity functions of reaction kinetic models
J.Phys.Chem. A, 107,
2216-2238 (2003)
ABSTRACT
56 L. Haszpra, I. Lagzi, T. Turányi, A.S.Tomlin, G.
Radnóti
Nyári
szmog-helyzetek
előrejelzése adaptív rácsmodellel
(Forecast of summer smog
episodes using an adaptive grid model, in Hungarian)
Proceedings of 'Meteorológiai
Tudományos Napok 2002'
pp. 119-123 and Table
IX in: , A meteorológiai előrejelzések és alkalmazásaik
(Forecast in meteorology and
its applications), ed: J. Mika,
Országos Meteorológiai
Szolgálat, Budapest, 2002, ISBN 963 7702 86 5
ABSTRACT
57 I. Lagzi, T. Turányi, A.S. Tomlin, L. Haszpra.
Simulation
of the effect of the plume of Budapest on the photochemical air
pollutants formation in Hungary
pp. 55-57 in: Proceedings
of the 4th International Conference on Urban Air Quality
23-27 March, 2003, Prague, R.S.
Sokhi and J. Brechler (eds.)
ABSTRACT
58 I. Gy. Zsély, J. Zádor and T. Turányi
Local
and global similarity of sensitivity vectors of combustion kinetic
models
pp. 849-859 in: Proceedings
of the 3rd Mediterranean Combustion Symposium,
Marrakech, Morocco, June 8-13,
2003
Editors: F. Beretta and A.
Bouhafid
ABSTRACT
59 T. Perger, T. Kovács, T. Turányi, C. Trevińo
Determination
of adsorption and desorption parameters from heterogeneous ignition
temperature measurements
pp. 860-870 in: Proceedings
of the 3rd Mediterranean Combustion Symposium,
Marrakech, Morocco, June 8-13,
2003
Editors: F. Beretta and A.
Bouhafid
ABSTRACT
60 I. Lagzi, T. Nagy, T. Turányi, L. Haszpra, A.S.
Tomlin
Simulation
of the formation and spread of photochemical air pollution in Hungary
pp. 495-500 in: Proceedings
of the Conference on Modelling Fluid Flow (CMFF'03)
Budapest, Hungary, September 3
- 6, 2003
ABSTRACT
61 Kovács T., Turányi T.
Modelling
of the decomposition of CCl4 in thermal plasma
in: Proceedings of the
2nd International Meeting on Chemistry,
3-6 June, 2003, Santa Clara,
Cuba
ISBN 959-250-080-0
ABSTRACT
62 R. Deters, H. Gg. Wagner, Á. Bencsura, K. Imrik, S.
Dóbé, T. Bérces, F. Márta, F. Temps, T. Turányi, I. Gy. Zsély
Direct
kinetic determination of rate parameters for the reaction CH3 + OH.
Implications for methane flame modelling
Proceedings of the European
Combustion Meeting 2003, Paper No. 21
ABSTRACT
63 I. Gy. Zsély, J. Zádor, T. Turányi
Uncertainty
analysis backed development of combustion mechanisms
Proceedings of the European
Combustion Meeting 2003, Paper No. 35
ABSTRACT
64 I. Gy. Zsély, T. Turányi
The
influence of thermal coupling and diffusion on the importance of
reactions:
The
case study of hydrogen-air combustion
Phys.Chem.Chem.Phys., 5,
3622-3631(2003)
ABSTRACT
65 I. Lagzi, D. Kármán, T. Turányi, A.S. Tomlin, L.
Haszpra
Simulation
of the dispersion of nuclear contamination using an adaptive Eulerian
grid model
J. Environm. Radioact.,
75, 59-82(2004)
ABSTRACT
66 J. Zádor, I. Gy. Zsély, T. Turányi
Investigation
of the correlation of sensitivity vectors of hydrogen combustion models
Int.J.Chem.Kinet., 36,
238-252(2004)
ABSTRACT
67 R. Lovas, P. Kacsuk, I. Lagzi, T. Turányi
Unified
development solution for cluster and grid computing and its application
in chemistry
Lecture Notes Comp. Sci.,
3044, 226-235(2004)
ABSTRACT
68 T. Turányi, I. Gy. Zsély, and J. Zádor
Selforganization
in high temperature reaction kinetic systems
pp. 134-137, in:
Proceedings of the conference "Selforganization in nonequilibrium
systems"
Slobodan Anic, Zeljko Cupic,
Ljiljana Kolar-Anic (eds.)
(Belgrade, September 24-25,
2004), ISBN: 86-82475-15-4
ABSTRACT
69 I. Gy. Zsély, J. Zádor, T. Turányi
Uncertainty
analysis
of updated hydrogen and carbon monoxide oxidation mechanisms
Proc. Combust. Inst., 30,
1273-1281(2005)
ABSTRACT
70 I. Lagzi, R. Mészáros, L. Horváth, A.S.
Tomlin, T. Weidinger, T. Turányi, F. Ács, L. Haszpra
Modelling
ozone fluxes over Hungary
Atm. Environm., 38,
6211-6222 (2004)
ABSTRACT
71 J. Zádor, I. Gy. Zsély, T. Turányi
Local
and global uncertainty analysis of complex chemical kinetic systems
Rel. Engng. Syst. Safety,
91, 1232–1240 (2006)
ABSTRACT
72 I. Lagzi, R. Lovas, T. Turányi
Development
of a Grid enabled chemistry application
in: Distributed and
Parallel Systems: Cluster and Grid Computing, Z. Juhasz; P. Kacsuk; D.
Kranzlmuller (Eds.)
The Kluwer International
Series in Engineering and Computer Science,
777, 137-144(2004),
ISBN: 0-387-23094-7
ABSTRACT
73 T. Kovács, T. Turányi, K. Föglein, J. Szépvölgyi
Kinetic
modelling of the decomposition of carbon tetrachloride in thermal plasma
Plasma Chemistry and Plasma
Processing, 25, 109-119(2005)
ABSTRACT
74 T. Perger, T. Kovács, T. Turányi, C. Trevińo
Determination
of the adsorption and desorption parameters for ethene and propene
from
measurements of the heterogenous ignition temperature
Combustion and Flame, 142,
107-116(2005)
ABSTRACT
75 I. Gy. Zsély, J. Zádor, T. Turányi
On
the similarity of the sensitivity functions of methane combustion models
Combustion Theory and
Modelling, 9, 721-738(2005)
ABSTRACT
76 J. Zádor, I. Gy. Zsély, T. Turányi, M. Ratto, S.
Tarantola, A. Saltelli
Local
and global uncertainty analyses of a methane flame model
J. Phys. Chem. A, 109,
9795-9807(2005)
ABSTRACT
77 I. Gy. Zsély, I. Virág, T. Turányi
Investigation
of a methane oxidation mechanism via the visualization of element fluxes
Paper IX.4 in: Proceedings
of the 4th Mediterranean Combustion Symposium,
Lisbon, Portugal, 5-10 October,
2005
Editors: F. Beretta, N. Selçuk,
M.S. Mansour
ABSTRACT
78 T. Kovács, T. Turányi, K. Föglein, J. Szépvölgyi
Modelling
of Carbon Tetrachloride Decomposition in Oxidative RF Thermal Plasma
Plasma Chemistry and Plasma
Processing, 26,
293-318(2006)
ABSTRACT
79 I. Lagzi, A. S. Tomlin, T. Turányi, L. Haszpra
Photochemical
air pollutant formation in Hungary using an adaptive gridding technique
Int.J. Environment and
Pollution, 36, 44-58(2009)
ABSTRACT
80 R. Mészáros, D. Szinyei, Cs. Vincze, I. Lagzi, T.
Turányi, L. Haszpra, A. S. Tomlin
Effect
of
the soil wetness state on the stomatal ozone fluxes over Hungary
Int.J. Environment and
Pollution, 36,
180-194(2009)
ABSTRACT
81 J. Zádor, T. Turányi, K. Wirtz, M. J. Pilling
Measurement
and investigation of chamber radical sources in the European
Photoreactor (EUPHORE)
J. Atmos. Chem., 55, 147-166(2006)
ABSTRACT
82 R. Lovas, J. Patvarczki, P. Kacsuk, I. Lagzi, T.
Turányi, L. Kullmann, L. Haszpra, R. Mészaros, A. Horányi, A. Bencsura,
Gy.Lendvay:
Air
pollution
forecast on the HUNGRID infrastructure
Gerhard R. Joubert, Wolfgang E.
Nagel, Frans J. Peters, Oscar G. Plata, P. Tirado, Emilio L. Zapata
(Eds.), ISBN 3-00-017352-8
Parallel Computing: Current &
Future Issues of High-End Computing, John von Neumann Institute for
Computing, Julich, Germany 2005,
NIC
Series, 33, 121-128
(2006)
ABSTRACT
83 T. Kovács, I. Gy. Zsély, Á. Kramarics, T.
Turányi
Kinetic
analysis of mechanisms of complex pyrolytic reactions
J.
Anal. Appl. Pyrolysis, 79,
252-258(2007)
ABSTRACT
84 A. Lovrics, A. Csikász-Nagy, I. Gy. Zsély, J. Zádor,
T. Turányi, B Novák
Time
scale
and dimension analysis of a budding yeast cell cycle model
BMC
Bioinformatics, 7:494(2006)
ABSTRACT
140 Viktor Samu; Tamás Varga; Igor Rahinov; Sergey Cheskis; Tamás
Turányi
Determination
of rate parameters based on NH2 concentration profiles
measured in ammonia-doped methane?air flames
Fuel,
212, 679-683 (2018)
https://doi.org/10.1016/j.fuel.2017.10.019
ABSTRACT
142 Noémi Buczkó, Tamás Varga, István Gyula Zsély; Tamás Turányi
143 R. Langer, A. Cuoci, L. Cai, U. Burke, C. Olm, H. Curran,
T. Turányi, H. Pitsch
A Comparison of Numerical
Frameworks for Modelling Homogenous Reactors and Laminar Flames
Proceedings of the Joint
Meeting of the German and Italian Sections of The Combustion Institute
(23-26 May, 2018,
Sorrento, Italy)
ABSTRACT
144 Martin Bolla, Carsten Olm, Tibor Nagy, István Gy. Zsély,
Tamás Turányi
Testing
several butanol combustion mechanisms against a large set of
experimental data and investigation of thermochemical data inconsistency
Proceedings
of the European Combustion Meeting – 2019, Paper S5_AII_05, 14-17
April, Lisbon, Portugal
ABSTRACT
145 Peng Zhang, István Gyula Zsély, Viktor Samu, Tamás Turányi
Comparison
of methane combustion mechanisms based on shock tube and RCM ignition
delay time measurements
Proceedings
of the European Combustion Meeting – 2019, Paper S3_AII_10, 14-17
April, Lisbon, Portugal
ABSTRACT
146 Márton Kovács, Tamás Varga, Carsten Olm, Ágota Busai, Róbert
Pálvölgyi, István Gy. Zsély, Tamás Turányi
Determination
of the rate parameters of N/H/O elementary reactions based on H2/O2/NOx
combustion experiments
Proceedings
of the European Combustion Meeting – 2019, Paper S3_AII_15, 14-17
April, Lisbon, Portugal
ABSTRACT
147 András Gy. Szanthoffer, István Gy. Zsély, Tamás Turányi
Comparison
of detailed NOx reaction mechanisms on syngas combustion systems
Proceedings
of the European Combustion Meeting – 2019, Paper S3_AII_11, 14-17
April, Lisbon, Portugal
ABSTRACT
148 C. Trevińo, T. Turányi
Low
temperature first ignition of n-butane
Combust.
Theory Modeling, 23, 1150-1168 (2019)
https://doi.org/10.1080/13647830.2019.1642519
ABSTRACT
149 Márton Kovács, Máté Papp, István Gyula Zsély, Tamás Turányi
Determination
of rate parameters of key N/H/O elementary reactions based on H2/O2/NOx
combustion experiments
Fuel, 264,
116720 (2020)
https://doi.org/10.1016/j.fuel.2019.116720
ABSTRACT
150 L. Kawka, G. Juhász, M. Papp, T. Nagy, I. Gy. Zsély, T.
Turányi
Comparison
of detailed reaction mechanisms for homogeneous ammonia combustion
Zeitscrift für
Physikalische Chemie, 234, 1329–1357 (2020) , https://doi.org/10.1515/zpch-2020-1649
ABSTRACT
151 É. Valkó, T. Turányi
Uncertainty
Quantification of Chemical Kinetic Reaction Rate Coefficients,
pp. 35-44 in:
Mathematical Modelling in Real Life Problems. Case Studies from
ECMI-Modelling,
Ewald Lindner, Alessandra
Micheletti, Cláudia Nunes (Eds.), Springer, 2020
ABSTRACT
152 Márton Kovács, Máté Papp, István Gy. Zsély, Tamás Turányi
Main
sources of uncertainty in recent methanol/NOx combustion models
Int. J. Chem. Kinet.,
53, 884-900 (2021)
https://doi.org/10.1002/kin.21490
ABSTRACT
153 Tibor Nagy, Tamás Turányi
Minimal
Spline Fit: a model-free method for determining statistical noise of
experimental data series
Proceedings
of the European Combustion Meeting – 2021, Paper 336, 14-15
April, 2021, Naples, Italy
ABSTRACT
154 Márton Kovács, Tibor Nagy, Tamás Turányi
Investigating
novel strategies for parameter optimization on a methanol/NOx combustion
mechanism
Proceedings
of the European Combustion Meeting – 2021, Paper 337, 14-15
April, 2021, Naples, Italy
ABSTRACT
155 Peng Zhang, István Gy. Zsély, Viktor Samu, Tibor Nagy, Tamás
Turányi
Comparison of methane
combustion mechanisms using shock tube and rapid compression machine
ignition delay time measurements
Energy&Fuels,
35, 12329−12351 (2021)
https://doi.org/10.1021/acs.energyfuels.0c04277
ABSTRACT
156 Éva Valkó, Máté Papp, Márton Kovács, Tamás Varga, István Gy.
Zsély, Tibor Nagy, Tamás Turányi
Design
of combustion experiments using differential entropy
Combustion Theory
Modelling, 26, 67-90 (2022)
https://doi.org/10.1080/13647830.2021.1992506
ABSTRACT
157 Peng Zhang, István Gy. Zsély, Máté Papp, Tibor Nagy, Tamás
Turányi
Comparison of methane
combustion mechanisms using laminar burning velocity measurements
Combust. Flame, 238,
111867 (2022)
https://doi.org/10.1016/j.combustflame.2021.111867
ABSTRACT
158 Anhao Zhong, Xinling Lia, Tamás Turányi, Zhen Huang, Dong Han
Pyrolysis
and oxidation of a light naphtha fuel and its surrogate blend
Combust. Flame, 240,
111979 (2022)
https://doi.org/10.1016/j.combustflame.2021.111979
ABSTRACT
159 Csanád Kalmár, Tamás Turányi, István Gy. Zsély, Máté Papp,
Ferenc Hegedűs
The
importance of chemical mechanisms in sonochemical modelling
Ultrasonics
Sonochemistry, 83, 105925 (2022)
https://doi.org/10.1016/j.ultsonch.2022.105925
ABSTRACT
160 Éva Valkó, Máté Papp, Peng Zhang, Tamás Turányi
Identification
of homogeneous chemical kinetic regimes of methane-air ignition
. Proc.
Combust. Inst., 39, 467-476
(2023)
https://doi.org/10.1016/j.proci.2022.07.186
ABSTRACT
161 Márton Kovács, Máté Papp, Tamás Turányi, Tibor Nagy
A
novel active parameter selection strategy for the efficient optimization
of combustion mechanisms
. Proc.
Combust. Inst., 39, 5259-5267 (2023)
https://doi.org/10.1016/j.proci.2022.07.241
ABSTRACT
162 Simret Kidane Goitom, Máté Papp, Márton Kovács, Tibor Nagy,
István Gy. Zsély, Tamás Turányi, László Pál
Efficient
numerical methods for the optimization of large kinetic reaction
mechanisms
Combustion Theory Modelling,
26, 1071-1097 (2022)
https://doi.org/10.1080/13647830.2022.2110945
ABSTRACT
164 Martin Bolla, Máté Papp, Carsten Olm, Hannes Böttler, Tibor
Nagy, István Gy. Zsély, Tamás Turányi
Comparison
and analysis of butanol combustion mechanisms
Energy&Fuels, 36,
11154–11176 (2022)
https://doi.org/10.1021/acs.energyfuels.2c01529
ABSTRACT
165 Simret Goitom, Tamás Turányi, Tibor Nagy
Testing
various numerical optimization methods on a series of artificial test
functions
Annales Univ. Sci.
Budapest., Sect. Comp., 53 , 175–199 (2022)
ABSTRACT
166 András Szanthoffer, István Gyula Zsély, László Kawka, Máté
Papp, Tamás Turányi
Testing
of NH3/H2 and NH3/syngas Combustion
Mechanisms Using a Large Amount of Experimental Data
Applications in Energy and
Combustion Science (AECS), 14, 100127 (2023)
ABSTRACT
167 Tamás Turányi
Reaction kinetics of
hydrogen combustion
Chapter 2 in book:
Hydrogen
for future thermal engines, (ed: Efstathios - Alexandros Tingas),
Springer Nature, 2023
https://doi.org/10.1007/978-3-031-28412-0_2
ABSTRACT
168 Sven Eckart, István Gyula Zsély, Hartmut Krause, Tamás Turányi
Effect of the variation of
oxygen concentration on the laminar burning velocities of
hydrogen-enriched methane flames
International Journal
of Hydrogen Energy, 49, 533-546 (2024) DOWNLOAD
LINK
https://doi.org/10.1016/j.ijhydene.2023.08.217
ABSTRACT
169 Boyang Su, Máté Papp, István Gy. Zsély, Tibor Nagy, Peng
Zhang, Tamás Turányi
Comparison of the performance
of ethylene combustion mechanisms
Combust. Flame,
260, 113201 (2024)
https://doi.org/10.1016/j.combustflame.2023.113201
ABSTRACT
170 A. Gy. Szanthoffer, I. Gy. Zsély, L. Kawka, M. Papp, T.
Turányi
Testing of Reaction Mechanisms for
the Combustion of NH3/H2 Mixtures Using a Large
Amount of Experimental Data
Proceedings of the 11th
European Combustion Meeting 2023, 26-28 April, 2023, Rouen, France, Paper
436739
ABSTRACT
171 M. Kovács, H. Schuszter, M. Papp, I. Gy. Zsély, T. Turányi
Comparison of Recent Acetone
Combustion Mechanisms Based on Large Amount of Experimental Data
Proceedings of the 11th
European Combustion Meeting 2023, 26-28 April, 2023, Rouen, France, Paper
437295
ABSTRACT
172 M. Kovács, A. Gy. Szanthoffer, É. Valkó, P. Zhang, M. Papp, T.
Nagy, I. Gy. Zsély, T. Turányi
Recent Advancements in the Reaction
Kinetics Branch of the ReSpecTh Information System
Proceedings of the 11th
European Combustion Meeting 2023, 26-28 April, 2023, Rouen, France, Paper
440662
ABSTRACT
173 L. Horváth, S. Dong, C. Saggese, M. Papp, H. J. Curran,W.
J. Pitz, T. Turányi, T. Nagy
Mechanism Reduction-Assisted Kinetic
Parameter Optimization for the n-Pentanol Chemistry of the NUIGMech
Multifuel Combustion Mechanism
Proceedings of the 11th
European Combustion Meeting 2023, 26-28 April, 2023, Rouen, France, Paper
443080
https://www.coria.fr/wp-content/uploads/2023/04/443080.pdf
ABSTRACT
174 M. Kovács, M. Papp, T. Turányi, T. Nagy
A Novel Active Parameter Selection
Strategy for the Efficient Optimization of Combustion Mechanisms
Proceedings of the 11th
European Combustion Meeting 2023, 26-28 April, 2023, Rouen, France, Paper
443082
https://www.coria.fr/wp-content/uploads/2023/04/443082.pdf
ABSTRACT
175 B. Su, M. Papp, I. Gy. Zsély, T. Turányi
Comparison of the performance of
ethylene combustion mechanisms based on large number of indirect
measurements
Proceedings of the 15th
International Conference on Combustion Technologies for a Clean
Environment, June 25-29, 2023, Lisbon, Portugal
ABSTRACT
176 A. Gy. Szanthoffer, M. Papp, L. Kawka, I. Gy. Zsély, T. Turányi
Quantitative evaluation of the
performances of detailed combustion mechanisms on neat NH3 and
NH3/H2 combustion
Proceedings of the 2nd
Symposium on Ammonia Energy, Orleans, France, 11-13 July, 2023
ABSTRACT
179 Pengzhi Wang, Sirio Brunialti, Máté Papp, S. Mani Sarathy,
Tamás Turányi, Henry J. Curran, Tibor Nagy
Mechanism development for
larger alkanes by auto-generation and rate rule optimization: A case study
of the pentane isomers
. Proc. Combust. Inst.,
40, 105408 (2024)
https://doi.org/10.1016/j.proci.2024.105408
ABSTRACT
182 András Gy. Szanthoffer, Máté Papp, Tamás Turányi
Identification
of well-parameterised reaction steps in detailed combustion mechanisms –
a case study of ammonia/air flames
. Fuel, 380,
132938 (2024)
https://doi.org/10.1016/j.fuel.2024.132938
ABSTRACT
1 A. Császár, L.
Jicsinszky, T. Turányi
Generation of model reactions
leading to limit cycle behaviour
React.Kinet.Catal.Lett.,
18, 65-71(1981)
The system of differential equations by Feistel and Ebelig has been generalized. Some new formal kinetic reactions with two internal components, which may exhibit limit cycle behavior have been studied. Based upon the numerical integration of the deterministic models of these reactions the oscillatory character of the systems has been confirmed.
Exotic phenomena in the deterministic model of complex chemical reactions are studied on the basis of preliminarily reported results. It is shown that the absence of a special kind of autocatalysis, autoinhibition and cooperativity implies the existence of a unique, asymptotically stable, positive equilibrium point. The class of chemical reactions with gradient system as its deterministic model is delineated. A procedure is given for the construction of oscillatory reactions. A neurobiological application of one of the constructed models is shown.
An eigenvalue-eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for several species of a reacting system at several time points. The main advantage of this method lies in its ability to reveal those parts of the mechanism which consist of strongly interacting reactions, an to indicate their importance within the mechanism. Results can be used to solve three general kinetic problems. Firstly, an objective condition for constructing a minimal reaction set is presented. Secondly, the uncovered dependencies among the parameters are shown to confirm or deny validity of quasi-steady-state assumptions under the considered experimental conditions. Thirdly, taking into account only sensitivities of observed species, the analysis is used to yield error estimates on unknown parameters determined from the experimental observations, and to suggest the parameters that should be kept fixes in the estimation procedure. To illustrate we chose the will-known hydrogen-bromine reaction and the kinetics of formaldehyde oxidation in the presence of CO.
Principal component analysis is a general method of extracting kinetic information from the array of sensitivity coefficients computed for several species of a reacting system. Eigenvectors corresponding to small eigenvalues indicate unimportant reactions and/or the validity of simplifying kinetic assumptions, thereby enabling one to optimally reduce the mechanism. Application of the method to the Edelson-Field-Noyes mechanism of the Belousov-Zhabotinsky reaction yields Oregonator-type simple models and clearly shows the kinetic approximations required for such reduction. The relative significance of individual reactions in the EFN mechanism is also determined over different subintervals of the period.
A reaction mechanism called background model has been formuled which is intended to describe the photochemistry in the "unpolluted" troposphere i.e. in the relatively clean atmosphere not exposed to the direct perturbation from local emitting sources. The mechanism consist of 48 chemical reactions, including 12 photochemical steps, and 12 emission and deposition processes. Selection of the reactions included in the scheme has been based on competitive kinetic consideration using recent kinetic and photochemical parameters. The model has been applied to the computation of diurnal concentration profiles of the trace pollutants of the troposphere.
In the atmosphere the transformations of the nitrogen compounds are controlled by complicated non-linear interactions. Therefore, the relations between the emission, concentration and deposition can be described only by complex mathematical models. In the paper a model is presented by means of which the dependence of the concentration and the production rate of nitric acid on the chemical composition of the pollution emitted is studied. The calculations prove that there is no linear relation between the rate of the nitric acid production and nitrogen oxide concentration. The production rate and the concentration of nitric acid are influenced by the hydrocarbon emission/concentration.
A photochemical air pollution model suitable for urban air quality calculations has been developed and tested under realistic conditions. The model treats pollutant transport by adopting the Langrangian approach. Detailed chemistry is contained in the model which includes emission and deposition processes taken into account as first order steps. A recent version of sensitivity analysis is used to reduce the original reaction mechanism to a favourable size.
A new sensitivity analysis technique is developed by utilizing Tihonov's singular pertubation theory. The described sensitivity analysis method deals with algebraic equations instead of solving the system of differential equations, which is the case in conventional sensitivity analysis. In the field of chemical kinetics, the proposed technique can supply information on the importance of elementary steps in complex reaction mechanisms. As examples, high-temperature propane pyrolysis and the chemistry of the "unpolluted" troposphere are studied.
Exploratory measurements for the detection of the photochemical
contamination of the air were carried out by co-workers of the Central
Research Institute for Chemistry, of the Institute of Atmospheric Physics
and of the National Institute of Public Health on seven work-days in
Budapest, between August 17 and September 2, 1987. A measuring point was
established on the flat roof of the National Institute of Public Health,
where the hydrocarbon and aldehyde contamination and the total oxidant
content of the air was measured and by the use of a recorder, the nitrogen
oxide concentration of the air was monitored.
According to the measurements, the hydrocarbon concentration of the air is
rather high (400-1800 ppbC) in the mornings and formaldehyde concentration
shows disquietingly high values (10-180 ppb). The atmospheric total
oxidant concentration did not exceed the acceptable level (10-120 ppb) in
spite of the sunny summer weather. However, the measured high nitrogen
oxide and hydrocarbon concentrations render probable that outside the
towns, in the main current of the town contamination, high oxidant
concentration may develop, endangering both the agricultural production
and the natural vegetation.
The placement of the measuring point and the average weather conditions
without extremities make probable that the measurements represent the
average contamination conditions of a larger area.
Using the elementary sensitivity densities, a reaction rate sensitivity gradient is obtained which is the derivative of the rate of species concentration change with respect to the rate coefficient. The dimensionless (log-normalized) form of the reaction rate sensitivity gradient is the ratio of the rate of concentration change of species i due to elementary reaction j and the net rate of concentration change of species i. This result provides a mathematical basis for the use of various forms of reaction rate analyses. The method is used to analyze the mechanism of high-temperature formaldehyde oxidation and high-temperature propane pyrolysis. Ranking of the elementary reactions allowed us to reduce significantly the original mechanisms and a detailed study of the results revealed the reaction structures and the major reaction paths of the species.
A reaction mechanism suggested for the description of the kinetics in the unpolluted troposphere was investigated by rate sensitivity and concentration sensitivity analyses. The study resulted in a 50-step reduced model and revealed the change of the importance of reactions during a diurnal cycle.
An updated mechanism for the Briggs-Rauscher reaction (also known as "Iodine Clock" reaction) has been investigated by the principal component analysis of the rate sensitivity matrix. The analysis revealed that five reactions of the 15-step model were redundant. The results of principal component and of rate-of-production analyses together gave an insight into the basic processes of the "Iodine Clock" reaction.
A program package is provided for analysis of kinetic mechanisms on personal computers. KINAL consists of four programs called DIFF, SENS, PROC and YRED. These require similar input data and use common subroutines. DIFF solves stiff differential equations and SENS computes the local concentration sensitivity matrix. PROC generates the rate sensitivity matrix of the quasi-stationary sensitivity matrix from concentration data or uses a matrix computed by SENS and extract the kinetic information inherent in sensitivity matrices by principal component analysis. Finally, YRED provides suggestions for the elimination of species from the reaction mechanism.
Systematic methods for mechanism reduction published so far consider each
species equally important and therefore these
methods do not eliminate species from a mechanism even if they are
insignificant. Two methods are given here for the
identification of species, which are necessary for the description of the
concentration changes of important species. A reduced mechanism is
obtained if the important reactions of important and necessary species are
identified by the principal component analysis of the normed algebraic
rate sensitivity matrix. As an example, the well-known low-temperature
alkane pyrolysis model of Edelson and Allara, consisting of 98 reactions
and 36 species, is reduced to a mechanism for propane pyrolysis which
includes 38 reactions of 13 species. The deviations between the two models
are in the order of half percent, while the computer time requirement for
the solution of the reduced model is about one tenth compared to that of
the full model.
Sensitivty analysis investigation the effect of parameter change on the solution of mathematical models. In chemical kinetics, models are usually based on differential equations and the results are concentration-time curves, reaction rates, and various kinetic features of the reaction. This review discusses in detail the concentration sensitivity, rate sensitivity, and feature sensitivity analysis of spatially homogeneous constant-parameter reaction systems. Sensitivity analyses of distributed parameter systems and of stochastic systems are also briefly described. Special attention is paid to the interpretation of sensitivity coefficients which can provide information about the importance and interconnection of parameters and variables. Applications of sensitivity analysis to uncertainty analysis, parametric scaling, parameter estimation, experimental design, stability analysis, repro-modelling, and investigation and reduction of complex reaction mechanisms are discussed profoundly.
The reactions constituting the mechanism of the oscillatory Belousov-Zhabotinskii (BZ) reaction may be divided into an inorganic and an organic subset. The former is well established and generally accepted, but the latter remains under development. There has been considerable work on component reactions of the organic subset over the past few years, but little effort has been made to incorporate the results of this work into an improved BZ mechanism. We do so and present a BZ mechanism containing 80 elementary reactions and 26 variable species concentrations and which implements recent experimental results and suggestions concerning the complicated organic chemistry, involved. The possible role of organic radicals as a second control intermediate is explored. The rate constants of the inorganic subset also are adjusted for acidity effect. The performance of the model in simulating either quantitatively of semiquantitatively a number of recent BZ experiments is substantially better than that of pervious models. Several areas in need of further work are identified.
An 80-reaction, 26-species mechanistic model of the oscillatory Belousov-Zhabotinsky (BZ) reaction recently introduced by Gyorgyi, Turányi and Field (GTF model) is analyzed in this work. Major reaction interactions within the large mechanism are revealed, and by reaction rate sensitivity analysis redundant species and reactions are identified. Removal of these results in a 42-reaction, 22-species mechanism that quantitatively agrees with the original model in three test simulations. This mechanism was further simplified to 3-variable (HBrO2, Br-, Ce(IV)) skeleton models that are oscillatory under the conditions where the transient oscillations appear in the batch simulations. Two such models are put forward that oscillate without any change in the original parameter values. These skeleton models are contrasted with the Oregonator model and proved to be better description of the experimental system. It is of particular interest that these simple models do not contain any adjustable parameters. The 42-reaction mechanism is suggested as a starting point for further modeling studies with the BZ reaction. This model still contains both negative feedbacks suggested for this system, the bromide-control and the organic radical control. In the skeletons only the inhibition by bromide ions is necessary for the oscillations to occur. The simplification process reveals that the radical transfer process between malonyl radical and bromomalonic acid is of great importance in this mechanism. Recent experimental study by Forsterling and Stuk finds this reaction to be unimportant in the BZ chemistry. We propose the addition of the hydrolysis of bromomalonyl radical to the GTF model to deal with the problem and with that provide an alternative interpretation for the above experiments.
A laser flash photolysis/resonance fluorescence investigation has been
carried out to study the kinetics of the overall
reactions OH + cyclopropane (1) and OH + cyclobutane (2) in the
temperature range 298-490 K and at 298 K, respectively. The following
kinetic parameters have been determined: k1 = (3.9 +/- 0.6)10(-12) exp
{-(2.2 +/- 0.1)kcal mol-1/RT} molecule-1 cm3 s-1, k2(298 K) = (17.5 +/-
1.5)10(-13) molecule-1 cm3 s-1.
During three summer measuring campaigns the atmospheric concentration of non-methane hydrocarbons and aldehydes were measured at two sites in Budapest. Two hundred and forty-five flask samples were analyzed for non-methane hydrocarbon concentration and hydrocarbon composition. For formaldehyde and acetaldehyde concentration 185 and 122 samples were analyzed, respectively. The total non-methane hydrocarbon concentration shows a characteristic diurnal variation with a peak between 6 a.m. and 9 a.m. At the two sites the average concentrations between 6 a.m. and 9 a.m. are 802 and 606 ppbC, respectively. Comparing the speciation of hydrocarbons in the air of Budapest with that measured in other cities we have realized a relative surplus in C6 alkanes which is balanced by the low contribution of C3-C4 alkanes. Both the formaldehyde and acetaldehyde concentration were found rather high. In the downtown the average concentrations are 10.4 and 4.4 ppb, while 3 km away from the center of the city the corresponding values are 28.0 and 5.8 ppb.
Tropospheric ozone has two origins: (i) transport from the stratosphere and (ii) O3 is a product of the NOx catalized photooxidation of airbone organic compounds. The concentration and the spatial and temporal distribution of ozone is determined by the intensity of the emission of primary pollutants, by the composition of emitted gases and by meteorological factors. Results of measurements and of model calculations for Budapest and for the surrounding areas are presented. The model calculations show that the rural areas near Budapest are highly polluted by ozone. Results of model calculations also indicate that the level of pollution expected in the future to improve significantly with the decrease of the number of vehicles equipped with two-stroke engines.
A strategy for reducing complex chemical reaction mechanisms is developed
and illustrated with reference to the oscillatory H2 + O2 system in a CSTR
in the region of the second explosion limit. The approach involves the
identification of redundant
species via rate sensitivity analysis and of redundant reactions by the
principal component analysis of the rate sensitivity matrix. Temperature
sensitivity analysis is also employed and the application of the
quasi-steady-state approximation is discussed briefly and used in the
final stages of the reduction. The above procedures are shown to assist
the understanding of the underlying mechanisms of the reaction for the
chosen conditions and the competition between branching steps during
oscillatory ignitions is discussed. The reduced mechanism is compared with
models discussed elsewhere.
The rate constant for the isomerisation reaction neo-C5H11O2 =>
C5H10OOH (k3) has been determined directly over the temperature range
660-750 K. neo-C5H11I was photolysed at 248 nm using a KrF laser in the
presence of O2 and He. The alkyl radical generated in the photolysis
reacts with O2 to form the peroxy radical which then isomeries to the
hydroperoxy radical. Subsequent raped reactions lead to the generation of
OH, which was detected by laser induced fluorescence as a function of
time. At high [O2] the time constant, lambda+, for the build up of OH
tends to -k3. As [O2] decreases, earlier reactions in the peroxy radical
chain become important and analysis of the [O2] dependence of lambda+,
allows both k3 and k2, the rate constant for the peroxy radical
decomposition, to be determined. Data analysis shows that the results are
fully compatible with the steady-state measurements of Baldwin et al except
that values for k3 a factor of over ten lower that their values are
obtained. The discrepancy is shown to due to errors in the equilibrium
constant, K2, they used for the (R2) reaction.
Application of the quasi-steady-state approximation (QSSA) in chemical
kinetics allows the concentration of some species
(QSSA species) to be calculated not only via the solution of kinetic
differential equations but also from the concentration
of other species using algebraic equations. The difference in the
concentrations of QSSA species obtained from the two
calculations, at a single time point, is called the instantaneous QSSA
error. This error represents a continuous perturbation of the calculated
trajectory and causes an overall error in the concentrations of non-QSSA
species as well. Two equations are given for the calculation of the
instantaneous error. Initial selection of QSSA species can be based on the
first equation, which predicts the instantaneous error of a single
species. The second more involved error equation takes into account the
interaction of errors of selected species and gives the instantaneous
error for a group of QSSA species. Successful application of the QSSA
requires that the overall error of important species be small. In some
cases a small instantaneous error in the QSSA species can be magnified and
results in large overall error. Such ''pathological'' cases can be
detected by the calculation of the initial concentration sensitivity
matrix. Those species, which induce large overall error, have to be
excluded from the group of the QSSA species. The relation of the QSSA to
the lifetime of species and to the stiffness of ODEs is also discussed.
The use of the error formulas is illustrated by the application of the
QSSA for a propane pyrolysis mechanism and briefly for the combustion of
H2.
The kinetics of the reactions of hydroxy radicals with cyclopropane and
cyclobutane has been investigated in the
temperature range of 298-492 K with laser flash photolysis/resonance
fluorescence technique. The temperature dependence of the rate constants
is given by k1 = (1-17 +/- 0.15) x 10(-16) T3/2 exp[-(1037 +/- 87) kcal
mol-1/RT] cm3 molecule-1 s1 and k2 = (5.06 +/- 0.57) x 10(-16) T 3/2
exp[-(228 +/- 78) kcal mol-1/RT] cm3 molecule-1 s-1 for the reactions OH +
cyclopropane --> products (1) and OH + cyclobutane --> products (2),
respectively. Kinetic data available for OH + cycloalkane reactions were
analyzed in terms of structure-reactivity correlations involving kinetic
and energetic parameters.
Nowadays, the application of models comprising several hundred of several thousand chemical reactions became wide-spread in chemical kinetics especially for the description of combustion and atmospheric chemical processes. Application of partial differential coefficients, derived from the kinetic differential equation, is discussed for the identification of important reactions and rate limiting steps and or the new generalize interpretation of chein length and life time of species. Based on a new interpretation of the quasi-steady-state approximation (QSSA), equations were derived for the accurate estimation of the error of QSSA.
Due to the growing need for the simulation of distributed parameter systems, the method of quasi-steady-state approximation (QSSA) has been revitalized. The wide-spread use of the QSSA is hindered because of the lack of a general condition for the application of the QSSA for kinetic systems of arbitrary size. An early article of Frank-Kamenetskii gave such a condition but this work remained almost completely unknown. This paper is commented here in the light of recent results of chemical kinetics and of the theory of differential equations. The English translation of the complete original paper (Frank-Kamenetskii,D.A., Zh.Fiz.Him., 14, 695(1940) ) is also presented.
Thermolysis of methanol in the presence of oxygen was investigated by
computational modelling and sensitivity
analysis in the temperature interval 900 K less-than-or-equal-to T
less-than-or-equal-to 1100 K and at reaction times 10(-5) s <= t <=
1 s. Based on earlier experimental investigations and new kinetic data, a
complex mechanism was set up to clarify the formation of formaldehyde,
glycol, carbon monoxide, water, acetaldehyde, and formic acid, and the
role of the radicals CH2OH, CH3, CHO, C2H3O, H, and O in the kinetic
process. The resulting mechanism of 48 reactions and 20 species was
reduced to 32 reactions and 17 species at 900 K and to 31 reactions and 17
species at 1000 K and at 1100 K. The results of simulations were compared
to the experimentally measured concentrations of the pyrolytic products.
29 T. Turányi, L. Györgyi
Investigation of complex
reaction mechanisms by sensitivity analysis
pp. 298-320 (in Hungarian)
in: Non-linear dynamics and
exotic kinetic phenomena in
chemical systems ( Ed. Gy.
Bazsa)
Debrecen-Budapest-Godollo, 1992
The two-channel thermal decomposition of 1,1,2,2-tetrafluorocyclobutane
(TFCB) and 1-methyl-2,2,3,3-
tetrafluorocyclobutane (MTFCB) have been studied in the temperature range
of 730-805 K at pressures varied from 1.1 Pa
up to 4.6 kPa. In the pressure independent range, Arrhenius expressions
were obtained for TFCB decomposition into 2 CH2CF2 (k1) and C2H4 + C2F4
(k2), respectively. The same kinetic equations were determined for the
decomposition of MTFCB into C3H4F2 + C2H2F2(k3) and C3H6 + C2F4 (k4). From
the study of the pressure dependence of the homogeneous decomposition
rates, the average downward energy transfer values of 1800 +/- 200 cm-1
and 1600 +/- 200 m-1 were obtained for the TFCB and MTFCB molecules,
respectively.
The efficiency of gas/wall vibrational energy transfer has been studied over the temperature range 800-1100 K by the ''variable encounter'' method. The average energies transferred per deactiviting collisions with the wall were determined at 800 K to be 3200 cm-1 and 2900 cm-1 for the 1,1,2,2-tetrafluorocyclobutane (TFCB) and 1-methyl-2,2,3,3-tetrafluorocyclobutane (MTFCB) molecules, respectively. This energy increased strongly with decreasing temperature. A comparison is made of [DELTAE'] with previous results for related molecules.
Recent methods for mechanism reduction convert large detailed chemical reaction mechanisms into small systems of differential or differential-algebraic equations. A possible further step is the parameterization of reaction mechanisms, i.e. the description of chemical kinetics by explicit functions. obtained by numerical fitting to the numerical solution of differential equations A new parameterization procedure, based on orthonormal polynomials, is described which is well applicable for fitting high-order polynomials having few effective parameters. A program is provided for the generation of multivariate Horner equations. The method is illustrated by the parameterization of a recent version of the Oregonator, a skeleton model of the oscillating Belousov Zhabotinsky reaction.
The basic problem of mechanism reduction methods is to find functional
relationships between selected state variables (e.g., some concentrations
and temperature) and their rates. However, this information is present
during the simulations with the full chemical model.
As a new applications of the repro-modeling approach, information for
rates is extracted from detailed chemical calculations and stored in the
form of high-order multivariate polynomials. For an efficient utilization
of the polynomials, a computer program was written that rearranges them to
the form of multivariate Horner equations. The repro-modeling method is an
alternative to the application of the quasi-steady-state approximation
(QSSA) and of the low-dimensional manifold method. Pros and cons of these
three methods are discussed in detail considering the preparations
required, the accuracy attainable, the yield in computer time, and the
limitations of the techniques.
Simulations of the combustion of wet CO using two-variable and
three-variable repro-models were 24,000 and 11,700 times faster,
respectively, than the SENKIN calculation using the full model. These
calculations represent the first use of repro-modeling for combustion
mechanism reduction.
Chemical mechanisms have been employed in hydrocarbon combustion as a means of understanding the underlying phenomenology of the combustion process in terms of the elementary reactions of individual species. This chapter provides an introduction to most of the mathematical methods that have been used for the construction, investigation, and reduction of combustion mechanisms. The use of algebraic manipulation in techniques, such as the quasi-steady-state approximation (QSSA) and lumping, make the production of a reduced mechanism essential and make subsequent calculations as simple as possible. Computational singular perturbation (CSP) is an alternative to the rate-of-production and sensitivity methods for mechanism reduction and provides an automatic selection of the important reactions as well as time-scale analysis. The simplest and most widely used technique involving the separation of time scales is the QSSA; however, a possible limitation is that it may not provide the minimum low-order system. Chemical lumping can prove very useful in areas, such as the combustion of hydrocarbon mixtures or soot formation. Several programs are available for the investigation and reduction of combustion mechanisms, including MECHMOD, a code for the automatic modification of CHEMKIN format combustion mechanisms, and KINALC, which is an almost automatic program for the investigation and reduction of gas-phase reaction mechanisms. KINALC is a postprocessor to CHEMKIN-based simulation packages SENKIN, PREMIX, OPPDIF, RUN1DL, PSR, SHOCK and EQLIB. Because models in combustion are expected to cover a wide range of conditions, it is natural to expect that a different approach might be used for different cases.
Two techniques, Artificial Neural Network (ANN) and Repro-Modelling (RM), are successfully used to represent the chemistry in turbulent combustion simulations. This is a novel application of both methods which show satisfactory accuracy in representing the chemical source term, and good ability in capturing the general behaviour of chemical reactions. The ANN model, however exhibits better generalisation feature over those of the RM approach. In terms of computational performance, the memory demand for handling the chemistry term is practically negligible for both methods. The total Central Processing Unit (CPU) time for Monte Carlo simulation of turbulent jet diffusion flame, which is dictated mainly by the time required to resolve the chemical reactions, is smaller if the RM method is used to represent the chemistry, in comparison to the time required by the ANN model. The potential and capabilities of these techniques are extendable to handle the chemistry of different fuels, and more complex chemical mechanisms.
The chemical equilibrium Br + CH3OH reversible arrow HBr + CH2OH (1, -1) has been studied by investigating the kinetics of the forward and reverse reactions. Excimer laser photolysis coupled with Br atom resonance fluorescence detection was used over the temperature range 439-713 K to obtain k(1) = (3.41 +/-0.89) x 10(9)T(1.5) exp[-(29.93 +/- 1.47) kJ mol(-1)/RT] cm(3) mol(-1) s(-1). The reverse reaction was studied with the fast flow technique, in the temperature range 220-473 K, using laser magnetic resonance for monitoring the CH2OH radicals. Thus, k(-1) = (1.20 +/- 0.25) x 10(12) exp[(3.24 +/- 0.44) kJ mol(-1)/RT] was obtained. The kinetic results were compared with available literature data and possible causes of the deviations were discussed. Kinetic information on the foward and back reactions was combined to obtain the heat of formation for CH2OH. Both second-law and third-law procedures were used in the derivations, giving a recommended value of Delta(f)H degrees(298)(CH2OH) = -16.6 +/- 1.3 kJ mol(-1), which corresponds to the C-H bond dissociation energy of DH degrees(298)(H-CH2OH) = 402.3 +/- 1.3 kJ mol(-1). These thermochemical data obtained from kinetic equilibrium studies agree within the error limits with current photoionization mass spectrometric and ab initio theoretical results.
Combustion chemical models usually contain several hundred or thousand
kinetic rate parameters. Most simulation packages
calculate local concentration sensitivities, but it is frequently not easy
to extract meaningful information from
large sensitivity matrices. Principal component analysis is a simple
post-processing technique that summarizes sensitivity
information and also reveals the effect of simultaneously changing
parameters. A new program package, called KINALC, has
been created for the analysis of gas-phase reaction systems. This program
is an extension to CHEMKIN based simulation
programs. KINALC processes the concentration sensitivity information in
four different ways and allows a comparison of
the sensitivity information to other methods, based on the study of
reaction rates and stoichiometry, for the analysis of
complex mechanisms. KINALC is available through the World Wide Web. The
various methods are illustrated by the analysis of a detailed chemical
model for hydrogen combustion. Local sensitivity analysis of models of
homogeneous hydrogen
explosion and of premixed laminar hydrogen-air flame has been carried out
and the sensitivity results reveal that the
chemical processes are very similar in these physically different systems
at the corresponding temperatures.
An induction parameter model has been constructed for the simulation of
shock-induced combustion that incorporates the
repro-modeling approach for the description of the energy release phase.
The model applies only explicit, algebraic
functions for the description of the chemical kinetics. These functions
parameterize a set of data calculated from
homogeneous combustion simulations using a complete and detailed reaction
mechanism. Based on this method a model has
been created for the simulation of shock-induced combustion of hydrogen in
an argon atmosphere. The parameterized model
approximates the results of the full chemistry very closely, but the
algebraic functions can be computed in a fraction of
the time of the full chemistry solution. We use the parameterized model in
one- and two-dimensional reactive flow
simulations. The results simulate experimental results well, including
transitions to detonations and the propagation of detonation waves.
In der Arbeit werden Ergebnisse einer numerischen Simulation einer
axialsymmetrischen, turbulenten nichtvorgemischten Wasserstoff-Jet-Flamme
präsentiert ud mit experimentellen Daten verglichen. Das Konzept des
Repromodellierens wird präsentiert und Resultate einer numerischen
Simulation eines perfekt vorgemischten Reaktors mit den Ergebnissen
detaillierter Chemie verglichen. Es wird aufgezeigt, wie sich chemische
Abläufe mittels Repromodellieren sehr genau beschreibne lassen.
Ebenso wird erläutert, wie gut sich Temperaturen aun Hauptspezies im
physikalischen Raum einer turbulenten Verbrennung mittles PDF Mehtode
abbilden lassen und wo Limitierungen seitens der Chemie auftreten, wenn
ein Ansatz mit Gleichgewichts-Chemie gewählt wird. Die Verwendung des
Repromodellierens für den Einsatz in turbulenten Verbrennungsvorgängen
wird diskutiert und anhand der Koppelung einer Trasportgleichung für die
PDF mit der Methode des Repromodellierens vorgestellt.
Reaction kinetics plays a central role in atmospheric and combustion
chemistry. Recent research in atmospheric chemistry have identified the
most sensitive parts of atmosphere and combustion research contributed to
the development of environment friendly technologies. Chlorofluorocarbons
and halons have proved dangerous and now risk of their surrogates is being
assessed. A good surrogate must have a fast reaction with radical OH and
the compound and all its decomposition products must be harmless. Sulphate
aerosols are among the species that control the IR balance of the Earth.
Kinetic pathways from organic sulphur compounds, emitted by marine plants,
to aerosols is being studied.
Investigation of the mechanisms of combustion of fuels, like hydrogen and
hydrocarbons, and fuel additives, like ethers, aldehydes and ketones, is
an active field. Development of low-NOx burners require the exploration of
the high temperature reaction kinetics of nitrogen compounds.
A comprehensive chemical mechanism to describe the oxidation of methane has been developed, consisting of 351 irreversible reactions of 37 species. The mechanism also accounts for the oxidation kinetics of hydrogen, carbon monoxide, ethane, and ethene in flames and homogeneous ignition systems in a wide concentration range. It has been tested against a variety of experimental measurements of laminar flame velocities, laminar flame species profiles, and ignition delay times. The highest sensitivity reactions of the mechanism are discussed in detail and compared with the same reactions in the GRI, Chevalier and Konnov mechanisms. Similarities and differences of the four mechanisms are discussed. Our mechanism is available on the World Wide Web as a fully documented CHEMKIN data file at the address http://www.chem.leeds.ac.uk/Combustion/Combustion.html
A detailed elementary reaction mechanism for nitrogen containing species in flames consisting of hydrogen, C1 or C2 fuels is presented. Simulation results obtained with this comprehensive NOx mechanism are compared with bulk experimental data obtained for nitrogen containing species in a variety of combustion systems including flow reactors, perfectly stirred reactors, and low pressure laminar flames. Sensitivity analysis has been employed to highlight the important reactions of nitrogen species in each system. The rate coefficients for these reactions have been compared against the expressions used in three other recent reaction mechanisms: version 3.0 of the GRI mechanism, the mechanism of Glarborg, Miller and co-workers, and that of Dean and Bozzelli. Comparisons indicate that there is still a large discrepancy in the reaction mechanisms used to describe nitrogen chemistry in combustion systems. Reactions for which further measurements and evaluations are required are identified and the differences between the major mechanisms available are clearly demonstrated.
A detailed chemical kinetic model was produced that described the high
temperature oxidative decomposition of CH3Br and HBr, and the formation of
tungsten bromide and oxide compounds in halogen lamps. The
Xe/Kr/W/Br/C/H/O mechanism consists of 52 reactive species and 395
irreversible reactions. A thermodynamic and transport database was set up
for all species of the mechanism.
A computational model was created for stationary modelling of long,
cylindrically symmetric halogen lamps. The model calculates the local
chemical composition as a function of distance from the filament taking
into account thermal reactions, photochemical reactions, ordinary and
thermal diffusion. It allows a systematic study of the effect of envelope
and filament geometry, filament and wall temperatures, pressure, and
composition of the gas on the radial tungsten transport and thus on the
lifetime of halogen lamps.
An adaptive grid model, describing the formation of photochemical oxidants based on triangular unstructured grids, has been developed for the Central European Region. The model automatically places a finer resolution grid in regions were higher numerical error is predicted by the comparison of 1st order and 2nd order solutions. Using this method, grid resolutions of the order of 15 km could be achieved in a computationally effective way. Initial simulation of the photochemical episode August 1998 indicate that the model captures well the spatial and temporal tendencies of ozone production.
An important tool in the management of photochemical smog episodes is a computational model which can be used to test the effect of possible emission control strategies. High spatial resolution of such a model is important to reduce the impact of numerical errors on predictions and to allow better comparison of the model with experimental data during validation. This paper therefore presents the development of an adaptive grid model for the Central European Region describing the formation of photochemical oxidants based on unstructured grids. Using adaptive methods, grid resolutions of less than 20 km can be achieved in a computationally effective way. Initial simulation of the photochemical episode of August 1998 indicates that the model captures the spatial and temporal tendencies of ozone production and demonstrates the effictiveness of adaptive methods for achieving high resolution model predictions.
Analyses of two methane oxidation mechanisms, the GRI mechanism (version 3.0) and the Leeds Methane Oxidation Mechanism (version 1.4), are reported here. Laminar premixed flames were simulated using program PREMIX, and redundant species and the redundant reactions were identified by program KINALC. Two series of reductions were carried out, where the aims were (i) the reproducton of flame speed, flame temperature and major speces concentratons and (ii) the reproducton of also the concentrations of radicals that play an important role in NOx production. The two mechanisms were investigated at fuel lean, stoichiometric and rich conditions. More than one hundred reactions could be eliminated in each case. Simulation results obtained by the reduced mechanisms dffer by a few pertent only from that calculated by the original mechanisms.
A method for assessing and comparing the impact of uncertainties in both
kinetic and thermodynamic parameters on the predictions of combustion
chemistry models has been developed. Kinetic, thermodynamic and overall
uncertainty parameters are defined, which allow tracking the sources of
uncertainties for a particular model result. The method was applied to
premixed laminar methane-air flames using the Leeds Methane Oxidation
Mechanism (
K.J. Hughes et al., Int.J.Chem.Kinet., 33,
513-538(2001)).
Heat of formation and rate coefficient data for species and elementary
reactions, respectively, related to methane combustion were collected from
several recent reviews and critically assessed error limits were assigned
to them. Local rate coefficient sensitivities and heat of formation
sensitivities were calculated for lean (phi = 0.62), stoichiometric (phi =
1.00) and rich (phi = 1.20) laminar atmospheric premixed methane-air
flames. Uncertainties of flame velocity, maximum flame temperature and
also the value and location of maximum concentration of radicals H, O, OH,
CH and CH2 were obtained from the sensitivities and the uncertainties of
thermodynamic and chemical kinetic data. The uncertainty of the calculated
flame velocity is typically 2-5 cm/s. Maximum flame temperature and
concentration of H, O, and OH can be calculated accurately, while there is
high uncertainty in the calculated maximum concentration of CH and CH2.
The calculations have revealed that the uncertainty of the calculated
flame velocity is caused mainly by errors of the input rate coefficients.
This is the case also for the calculated concentration of CH and CH2. The
uncertainty of the location of concentration maxima is also of kinetics
origin and it is caused by the very same rate coefficients that affect
flame velocity. Uncertainty of maximum adiabatic flame temperature and
maximum concentration of H, O and OH originates mainly from errors of the
input heat of formation data. In order to obtain good simulation results
for methane flames, accurate heats of formation are required in particular
for radicals OH, CH2(S), CH2, CH2OH, HCCO and CH2HCO. Simulation results
could be improved by better knowledge of the reaction rate parameters for
the reactions O2 + H = OH + O, O2 + H + M = HO2 + M, CO + OH = CO2 + H, H
+ CH3(+M) = CH4(+M), CH3 + OH = CH2(S) + H2O, C2H2 + OH = C2H + H2O and
C2H2 + CH = C2H + CH2. This conclusion is somewhat surprising since at
least the first three reactions are among the most frequently studied ones
in chemical kinetics.
The calculations demonstrate that all simulation results of chemical
kinetic modelling studies should be accompanied by uncertainty information
(e.g. standard deviation) for the model outputs to indicate which results
are well supported by the model and which ones are merely nominal values
that were obtained using the selected set of input parameters.
Effective procedures for the reduction of reaction mechanisms, including the intrinsic low-dimensional manifold (ILDM) and the repro-modelling methods, are all based on the existence of very different time scales in chemical kinetic systems. These two methods are reviewed and the advantages and drawbacks of them are discussed. An algorithm is presented for the repro-modelling based generation of ILDMs. This algorithm produces an unstructured table of ILDM points, which are then fitted using spline functions. These splines contain kinetic information on the behaviour of the chemical system. Combustion of hydrogen in air is used as illustrative example. Simulation results using the fitted model are compared with the outcome of calculations based on the detailed reaction mechanism for homogeneous explosions and 1D laminar flames.
Previous EUROTRAC investigations have shown that some of the highest regional ozone concentrations in Europe can be observed in Central Europe, including Hungary. Computational models are important tools in the management of photochemical smog episodes because they can be used for testing the effect of various emission control strategies. High spatial resolution of such models is very important to reduce the impact of numerical errors on predictions. Within a UK-Hungarian cooperation project a regional air quality model has been developed that describes the transport and chemical transformation of photochemical oxidants across Central Europe using an adaptive gridding method to achieve high resolution. The basic coarse grid covers a wider Central European region and a nested finer resolution grid covers Hungary. Further refinement of the unstructured triangular grid is invoked during the simulation at intermediate time-steps using spatial error estimators based on the comparison of high and low order numerical solutions of the atmospheric diffusion equation. Using this method, grid resolutions of the order of 20 km can be achieved in a computationally effective way within a domain of 1540 km X 1500 km.
Exposing a cold catalyst to a fuel-oxygen mixture, the surface gets covered with the more effectively adsorbing species. Increasing the temperature, this species is desorbed and the ignition temperature is determined by the rate of desorption. Based on the equations for the heat balance, expressions were derived for the calculation of ignition temperature from the parameters of the experimental setup, the preexponential factor Ad and activation energy Ed of desorption, the ratio of sticking coefficients, and the ratio of adsorption orders of fuel and oxygen. Published experimental data for the catalytic ignition of CO, H2 and CH4 were reinterpreted using the expressions obtained and the following parameters were determined for polycrystalline platinum catalyst: Ed(H2/Pt)=43.3±5.2 kJ/mole, Ed(CO/Pt)= 107.2±12.7 kJ/mole, Ed(O2/Pt)=190±34 kJ/mole, S(H2,0)/S(O2,0) =36.7±9.6, S(CO,0)/S(O2,0) =41.2±8.5, S(O2,0)/S(CH4,0) =5.9±0.3. Error limits refer to confidence level of 0.95. The activation energy of desorption for CO and O2 and the ratio of zero coverage sticking coefficients of O2 and CH4 are the first experimentally based determinations of these parameters. Experimental ignition temperatures could be reproduced assuming second order adsorption of CO, H2 and O2 on Pt surface. These reaction orders have been debated in the literature.
Local sensitivity functions d Y_i/d p_k of many chemical kinetic models exhibit three types of similarity: (i) Local similarity: ratio lambda_ij= (d Y_i/d p_k) /(d Y_j/d p_k ) is the same for any parameter k; (ii) The scaling relation: ratio lambda_ij is equal to (d Y_i/d z) /(d Y_j/d z ) ; (iii) Global similarity: ratio (d Y_i/d p_k) /(d Y_i/d p_m ) is constant in a range of the independent variable z. It is shown that the existence of low-dimensional slow manifolds in chemical kinetic systems may cause local similarity. Th scaling relation is present, if the dynamics of the system is controlled by a one-dimensional slow manifold. The rank of the local sensitivity matrix is less than or equal to the dimension of the slow manifold. Global similarity emerges if local similarity is present and the sensitivity differential equations are pseudohomogeneous. Global similarity means that the effect of the simultaneous change of several parameters can be fully compensated for all variables, in a wide range of the independent variable by changing a single parameter. Therefore, presence of global similarity has far-reaching practical consequences for the "validation" of complex reaction mechanisms, for parameter estimation in chemical kinetic systems, and in the explanation of the robustness of many self-regulating systems.
An adaptive grid model that describes the formation and transformation of photochemical oxidants, based on triangular unstructured grids has been developed to study the photochemical air pollution in the Central-European region. The model was applied here to investigate the influence of the emission of Budapest for the ozone concentration around the city. The two typical patterns are that (i) the high ozone precursor emission of Budapest causes a plume-like formation of ozone within about 100 km downwind even if no regional photochemical air pollution episode is present; (ii) in case of a regional zone episode, the large amount of NO emitted in Budapest significantly decreases the ozone concentration in the city. This latter influence is limited to a narrow region of Budapest. The model can be used for the elaboration of integrated ozone concentration maps for each year, which will allow a more comprehensive study of the emission of Budapest.
Local sensitivity functions (d Y_i/d p_k) of many chemical kinetic models exhibit three types of similarity: (i) local similarity: ratio lambda_ij= (d Y_i/d p_k) /(d Y_j/d p_k ) is equal for any parameter k; (ii) The scaling relation: ratio lambda_ij is equal to (d Y_i/d z) /(d Y_j/d z ) ; (iii) Global similarity: ratio (d Y_i/d p_k) /(d Y_i/d p_m ) is constant in a range of the independent variable z. Similarities can be detected by calculating the ratios above or, in a more efficient way, via the investigation of the correlations based on the scalar product of the corresponding sensitivity vectors. Local similarity may be a consequence of the existence of low-dimensional slow manifolds in chemical kinetic systems. Scaling relation may be present, if the dynamics of the system is controlled by a one-dimensional slow manifold. Global similarity emerges if local similarity is present and the sensitivity differential equations are pseudo-homogeneous. Global similarity means that the effect of the simultaneous change of several parameters can be fully compensated for all variables, in a wide range of the independent variable by changing a single parameter. The similarity relations are very important from a practical point of view in the fields of the 'validation' of complex reaction mechanisms and parameter estimation of chemical kinetic systems. Global similarity of models can be revealed by the principal component analysis of the sensitivity matrices. The statements are illustrated by numerical examples related to the homogeneous explosion and adiabatic laminar flames of stoichiometric methane-air mixtures.
In heterogeneous combustion, reaction of fuel and oxygen i occurs on a catalyst surface. The surface of a cold catalyst is covered with the more effectively adsorbing species; when the temperature is increased, this species is desorbed, and the rates of adsorption and desorption determine the ignition temperature. Based on the equations for the heat balance, expressions were derived for the calculation of ignition temperature from the parameters of the experimental setup and the physical parameters of adsorption and desorption. These physical parameters are the preexponential factor A_D and activation energy E_D of desorption, the ratio of zero coverage sticking coefficients, and the ratio of adsorption orders of fuel and oxygen. Several published experimental ignition temperature measurements were reanalysed to obtain adsorption-desorption parameters for CO, H2, CH4, C2H4, and C3H6 on polycrystalline platinum catalyst. The following parameters were determined via nonlinear least-squares fitting: activation energies of desorption: E_D(H2/Pt) = 43.3 ± 5.2 kJ/mol, E_D(CO/Pt) = 107.2 ± 12.7 kJ/mol, E_D(O2/Pt) = 190±34 kJ/mol, E_D(C2H4/Pt) = 136 ± 21 kJ/mol, E_D(C3H6/Pt) = 161 ± 53 kJ/mol; ratio of sticking coefficients: S(H2)/S(O2) = 36.7 ± 9.6, S(CO)/S(O2) = 41.2 ± 8.5, S(O2)/S(CH4) = 5.9 ± 0.3, S(C2H4)/S(O2) = 15.6 ± 1.9, S(C3H6)/S(O2) = 11.9 ± 1.7. Error limits refer to a confidence level of 0.95. Experimental ignition temperatures could be reproduced assuming second order adsorption of CO, H2, O2, CH4, C2H4, and C3H6 on polycrystalline platinum. These reaction orders have been debated in the literature.
An adaptive grid model has been developed to describe the formation of photochemical air pollutants in the Central European region. The modelled region covers an area of 1500 km × 1500 km with Hungary in the centre. Grid resolution in critical places can be as fine as 6 km. Vertical stratification of the troposphere, up to 3000 meters, is described by using four layers. The meteorological data used were obtained from the weather forecast model ALADIN of the Hungarian Meteorological Service. Simulation results are presented for a smog episode of 3rd and 4th August, 1998.
Perhalogenated hydrocarbons were popular materials in many areas of the chemical industry and in the household. Their applications have been banned by international treaties because of their stratospheric ozone depleting property. However, large quantities are still stored waiting for a safe decomposition technology. Many experimental articles were published in the last few years showing that plasma technology is applicable for the decomposition of halogenated hydrocarbons in an environmentally friendly way. We have modelled the kinetics of the decomposition of carbon tetrachloride in thermal plasma in argon bulk gas in the temperature range of 300 K to 7000 K. The reaction mechanism contains 34 irreversible reaction steps and 12 species. The thermodynamic data and the kinetic parameters were obtained from Burcat's Thermodynamic Database and the NIST Chemical Kinetics Database, respectively. The conditions of the modelling were in accordance with that was used in a recent experimental paper of Föglein et al. to allow the comparison of the modelling and the experimental results. The modelled reactor was an inductively coupled plasma (ICP) reactor. The CCl4/Ar mixture was injected to the high temperature (7000 K) region of the reactor. The modelled temperature profile was in accordance with that of the laboratory reactor. The kinetic calculations provided the concentration-time profiles for each species. All initial carbon tetrachloride was consumed within a few microseconds, but a part of the CCl4 was regenerated from the decomposition products. Our calculations predicted 70% net conversion of CCl4 , which is close to the experimentally determined 60%. Apart from the regenerated CCl4 , other main products of the incineration were C2Cl2 and Cl2. The simulations were also repeated by a thermodynamic equilibrium model. Results of the kinetic and thermodynamic modelling were in good accordance above 2000 K, but our calculations showed that below 2000 K the thermodynamic equilibrium model gave wrong predictions. Therefore, application of detailed kinetic mechanisms is recommended in the modelling of plasma incineration of harmful materials. Similar modelling studies can be used for planning efficient plasma reactors for incineration technologies.
Kinetics of the overall reaction CH3 + OH (1) were studied close to the high-pressure limit using the laser flash photolysis/transient UV absorption method (LFP/TAS) and in the fall-off regime with discharge flow/far infrared laser magnetic resonance (DF/LMR) at 298 K and 473 K, respectively. The product channel 1CH2 + H2O (1.1) was also studied with the DF/LMR method. The following rate constants and branching ratio were determined (in He): k1 (1463 mbar, 298 K) >= 6.2 10(13) cm3 mol-1 s-1 , k1 (1.16 mbar, 473 K) >= 5.2 10(13) cm3 mol-1 s-1 and k1.1 / k1 > 0.7 (1.16 mbar, 473 K). Flame velocity for a standard CH4-air flame was calculated in relation to the kinetics results.
Uncertainty analysis was used to back the development of H2/air and wet CO/air combustion mechanisms. The Leeds Methane Oxidation Mechanism was updated on the basis of the latest literature data. Uncertainties of the simulation results, caused by the uncertainties of the kinetic parameters and the heat of formation data, were analysed. The methods used were local uncertainty analysis and Monte Carlo Analysis with Latin Hypercube Sampling. There was always satisfactory agreement between the simulation results and the bulk experimental data, but in some cases the uncertainties of the simulation results were large.
Detailed chemical kinetic mechanisms are usually developed on the basis
of spatially homogeneous calculations, but utilized in the simulation of
very complex physical models. A fundamental question is if the importance
of reactions is determined solely by the temperature and the actual
concentration set or if it is also influenced by the thermal and diffusion
couplings present in the physical model. A 46-step detailed mechanism of
hydrogen oxidation was studied at equivalence ratios 0.5, 1.0, 2.0, and
4.0. Six physical models were designed (homogeneous explosion,
burner-stabilized and freely propagating laminar flames, with and without
thermal coupling), which provided very similar concentration curves as a
function of temperature, while the local sensitivity functions revealed
that the couplings in these models were very different. The importance of
the reactions in every model was investigated by the principal component
analysis of the rate sensitivity matrix F (PCAF method), exploiting that
the results of this method depend only on the concentrations and
temperature. A fundamentally different method, the principal component
analysis of the local sensitivity matrix S (PCAS method) was used to
extract information on the importance of reactions from the sensitivity
functions. The PCAF and PCAS methods selected identical reduced mechanisms
at all conditions, which shows that these are equally effective methods
for determining a minimal reduced mechanism. The good agreement between
the results of the two methods in the case of all models demonstrated that
the importance of reactions was independent of the physical model the
mechanism had been embedded into. Thermal coupling did not have an effect
on the selection of the reduced mechanisms. Difference between the
importance of reactions in explosions and flames were caused by the
difference of the concentrations in the low-temperature regions and not by
the presence of diffusion. The reduced mechanisms contained 15 to 28
reaction steps, depending on the equivalence ratio and the type of the
model. All species were retained in models of the combustion of lean and
stoichiometric mixtures, while species H2O2 could be eliminated at rich
conditions. Description of near stoichiometric conditions required more
reaction steps, while rich combustion could be described by few reactions.
An overall reduced mechanism, applicable in a wide range of conditions,
contained 31 reaction steps. Results of the PCAS method revealed the
global similarity relations of the sensitivity matrices of adiabatic
explosions.
Application of an Eulerian model using layered adaptive unstructured grids coupled to a meso-scale meteorological model is presented for modelling the dispersion of nuclear contamination following the accidental release from a single but strong source to the atmosphere. The model automatically places a finer resolution grid, adaptively in time, in regions were high spatial numerical error is expected. The high-resolution grid region follows the movement of the contaminated air over time. Using this method, grid resolutions of the order of 6 km can be achieved in a computationally effective way. The concept is illustrated by the simulation of hypothetical nuclear accidents at the Paks NPP, in Central Hungary. The paper demonstrates that the adaptive model can achieve accuracy comparable to that of a high-resolution Eulerian model using significantly less grid points and computer simulation time.
A well-established method for the analysis of large reaction mechanisms is the calculation and interpretation of the sensitivity of the kinetic model output Yi to parameter changes. Comparison of the sensitivity vectors si = {dYi /dp} belonging to differentmodel outputs is a new tool for kinetic analysis. The relationship of the sensitivity vectors was investigated in homogeneous explosions, freely propagating and burner-stabilized laminar flames of hydrogen-air mixtures, using either calculated adiabatic or constrained temperature profiles, for fuel-to-air ratios phi = 0.5-4.0. Sensitivity vectors are called locally similar, if the relationship s_i = lambda_ij*s_j is valid, where lambda_ij is a scalar. In many systems, only approximate local similarity of the sensitivity vectors exists and the extent of it can be quantified by using an appropriate correlation function. In the cases of adiabatic explosions and burner-stabilized flames, accurate local similarity was present in wide ranges of the independent variable (time or distance), and the correlation function indicated that the local similarity was not valid near the concentration extremes of the corresponding species. The regions of poor similarity were studied further by cobweb plots. The correlation relationships found could be interpreted by the various kinetic processes in the hydrogen combustion systems. The sensitivity vector of the laminar flame velocity is usually considered to be characteristic for the whole combustion process. Our investigations showed that the flame velocity sensitivity vector has good correlation with the H and H2O concentration sensitivities at the front of the adiabatic flames, but there is poor correlation with the sensitivity vectors of all concentrations in homogeneous explosions.
P-GRADE programming environment provides high-level graphical support to develop parallel applications transparently for both the parallel systems and the Grid. This paper gives an overview on the parallelisation of a simulation algorithm for chemical reaction-diffusion systems applying P-GRADE environment at all stages of parallel program development cycle including the design, the debugging, the execution, and the performance analysis. The automatic checkpoint mechanism for parallel programs, which supports the migration of parallel jobs between different clusters, together with the application monitoring facilities of P-GRADE enable the long-running parallel jobs to run on vARious non-dedicated clusters in the Grid while their execution can be visualised on-line for the user. The presented research achievements will be deployed in a chemistry Grid environment for air pollution forecast.
Models of homogeneous explosions and one-dimensional laminar flames of hydrogen and methane were analysed by a series of mathematical tools. The results indicated that the real dynamical dimension of these systems is 1 to 3, while the number of variables is from 10 to 38. This dimension reduction indicates strong couplings in the model, exhibited in the similarity relations among the sensitivity functions. It has consequences in areas of practical importance, like determination of rate parameters from experimental data or search for a minimal equivalent model.
Uncertainty analysis was used to investigate H2/air and wet CO/air combustion mechanisms. The hydrogen/carbon monoxide submechanism of the Leeds Methane Oxidation Mechanism was updated on the basis of the latest reaction kinetics and thermodynamics data. The updated mechanism was tested against three hydrogen oxidation and two wet CO bulk experiments. Uncertainties of the simulation results, caused by the uncertainties of the kinetic parameters and the heat of formation data, were analysed. The methods used were the local uncertainty analysis and Monte Carlo analysis with Latin hypercube sampling. The simulated flame velocity had relatively large uncertainty in both hydrogen-air and wet CO flames. In the case of ignition experiments, for both fuels the uncertainties of the simulated ignition delay times were small and comparable with the scatter of the experimental data. There was a good agreement between the simulation results and the measured temperature and concentration profiles of hydrogen oxidation in a flow reactor. However, accurate ignition delay is not a result of the flow reactor experiments. The uncertainty of the required time correction for matching the simulated 50% consumption of H2 to that of the experimental one (corresponding to the simulated ignition delay) was found to be very large. This means that very different parameter sets provide very different ignition delays, but very similar concentration curves after the time correction. Local uncertainty analysis of the wet CO flame revealed that uncertainties of the rate parameters of reactions O2 + H (+M) = HO2 (+M), and CO + OH = CO2 + H cause high uncertainty to the calculated flame velocity, temperature, and peak concentrations of radicals. Reaction H + HO2 = H2 + O2 also causes high uncertainty for the calculated flame velocity. The uncertainty of the enthalpy of formation of OH is highly responsible for the uncertainty of the calculated peak OH concentration.
This paper presents and utilises a coupled Eulerian photochemical reaction-transport model and a detailed ozone dry-deposition model for the investigation of ozone fluxes over Hungary. The reaction-diffusion-advection equations relating to ozone formation, transport and deposition are solved on an unstructured triangular grid using the SPRINT2D code. The model domain covers Central Europe including Hungary, which is located at the centre of the domain and is covered by a high-resolution nested grid. The sophisticated dry-deposition model estimates the drydeposition velocity of ozone by calculating the aerodynamic, the quasi-laminar boundary layer and the canopy resistance. The meteorological data utilised in the model were generated by the ALADIN meso-scale limited area numerical weather prediction model used by the Hungarian Meteorological Service. The ozone fluxes were simulated for three soil wetness states, corresponding to wet, moderate and dry conditions. The work demonstrates that the spatial distribution of ozone concentration is a less accurate measure of effective ozone load, than the spatial distribution of ozone fluxes. The fluxes obtained show characteristic spatial patterns, which depend on the soil wetness, the meteorological conditions, the ozone concentration and the underlying land use.
Computer modelling plays a crucial part in the understanding of complex chemical reactions. Parameters of elementary chemical and physical processes are usually determined in independent experiments and are always associated with uncertainties. Two typical examples of complex chemical kinetic systems are the combustion of gases and the photochemical processes in the atmosphere. In this study, local uncertainty analysis, the Morris method, and Monte Carlo analysis with Latin hypercube sampling were applied to an atmospheric and to a combustion model. These models had 45 and 37 variables along with 141 and 212 uncertain parameters, respectively. The toolkit used here consists of complementary methods and is able to map both the sources and the magnitudes of uncertainties. In the case of the combustion model, the global uncertainties of the local sensitivity coefficients were also investigated, and the order of parameter importance based on local sensitivities were found to be almost independent of the parameter values within their range of uncertainty.
P-GRADE development and run-time environment provides high-level graphical support to develop scientific applications and to execute them efficiently on various platforms. This paper gives a short overview on the parallelization of a simulator algorithm for chemical reaction-diffusion systems. Applying the same user environment we present our experiences regarding the execution of this chemistry application on nondedicated clusters, and in different grid environments.
Decomposition of carbon tetrachloride in a RF thermal plasma reactor was investigated under neutral conditions. The net conversion of CCl4 and the main products of its decomposition were determined from the mass spectrometric analysis of outlet gases. Flow and temperature profiles in the reactor were calculated and concentration profiles of the species along the axis of the reactor were estimated using a newly developed chemical kinetic mechanism, containing 12 species and 34 reaction steps. The simulations indicated that all carbon tetrachloride decomposed within a few mi-croseconds. However, CCl4 was partly recombined from its decomposition products. The calculations predicted 70 % net conversion of CCl4, which was close to the experimentally determined value of 60 %. The decomposition was also simulated by a thermodynamic equilibrium model. Re-sults of the kinetic and thermodynamic simulations agreed well above 2000 K. However, below 2000 K the thermodynamic equilibrium model gave wrong predictions. Therefore, application of detailed kinetic mechanisms is recommended for modelling CCl4 decomposition under thermal plasma conditions.
If a cold catalyst is exposed to a mixture of fuel + oxygen, the surface coverage of the catalyst can be dominated by either the fuel or the oxygen, depending on the actual catalyst and the composition of the gaseous mixture. If the temperature is increased, heterogeneous ignition occurs; the ignition temperature is influenced by the adsorption and desorption properties of both the fuel and the oxygen. Based on the equations for the heat balance, expressions have been derived for calculating the ignition temperature from the parameters of the experimental setup and the adsorption and desorption parameters of the fuel and the oxygen. These expressions can also be used to evaluate measured ignition temperatures to determine unknown adsorption and desorption parameters, such as: the pre-exponential factor AD and activation energy ED for the desorption of the dominant surface species, the ratio of the sticking coefficients and the ratio of adsorption orders of fuel and oxygen. This latter approach was used to evaluate measurements made by Cho and Law for the catalytic ignition of ethene and propene on polycrystalline platinum. The following parameters were determined by means of nonlinear least-squares fitting: ED(C2H4/Pt) = 136 ± 21 kJ/mol, ED(C3H6/Pt) = 161 ± 53 kJ/mol; S(C2H4,0)/S(O2,0)= 15.6 ± 1.9, S(C3H6,0)/S(O2,0)= 11.9 ± 1.7. Using a previously determined value for the sticking coefficient of O2, the values S(C2H4,0)= 0.38 ± 0.08 and S(C3H6,0)= 0.29 ± 0.06 were obtained. These error limits refer to a confidence level of 0.95. Experimental ignition temperatures could be reproduced assuming second order adsorption of ethene and propene on a surface of Pt.
It is widely known that detailed kinetic mechanisms with identical reaction steps but with very different rate parameters may provide similar simulation results in combustion calculations. This phenomenon is related to the similarity of sensitivity functions, which arises if low-dimensional manifolds in the space of variables, and autocatalytic processes are present. We demonstrated the similarity of sensitivity functions for adiabatic explosions and burner-stabilized laminar flames of stoichiometric methane.air mixtures. The cause of similarities was investigated by calculating the dimension of the corresponding manifolds, and the pseudo-homogeneous property of the sensitivity ODE. The methane explosion model showed global similarity, which means that different parameter sets could provide the same simulation results. This was demonstrated by numerical experiments, in which two significantly different parameter sets resulted in identical concentration profiles for all species. This is important from a practical point of view in the fields of the .validation. of complex reaction mechanisms and the parameter estimation of chemical kinetic systems.
Local and global uncertainty analyses of a flat, premixed, stationary, laminar methane flame model were carried out using the Leeds methane oxidation mechanism at lean (phi = 0.70), stoichiometric (phi = 1.00) and rich (phi = 1.20) equivalence ratios. Uncertainties of laminar flame velocity, maximal flame temperature, and maximal concentrations of radicals H, O, OH, CH and CH2 were investigated. Global uncertainty analysis methods included the Morris method, the Monte Carlo analysis with Latin hypercube sampling and an improved version of the Sobol' method. Assumed probability density functions (pdf) were assigned to the rate coefficients of all the 175 reactions and to the enthalpies of formation of the 37 species. The analyses provided the following answers: approximate pdfs and standard deviations of the model results, minimum and maximum values of the results at any physically realistic parameter combination, and the contribution of the uncertainty of each parameter to the uncertainty of the model result. The uncertainty of few rate parameters and few enthalpies of formation data cause most of the uncertainty of model results. Most uncertainty comes from the inappropriate knowledge of kinetic data, but the uncertainty caused by thermodynamic data is also significant.
Reaction pathway analysis is a frequently applied tool in the analysis and reduction of reaction mechanisms. Investigation of element fluxes is a rigorous way of kinetic pathway analysis. Code KINALC has been available for the post-processing of the output files of the CHEMKIN simulation programs. However, plotting the element flux figures provided by KINALC is very human time consuming, therefore a new reaction kinetics visualization tool, called FluxViewer has been developed. FluxViewer presents the species as boxes and the interconnecting reactions as arrows. Location of the boxes and the number of the arrows can be optimized in an interactive way. Development of oxidation processes in reactors and flames can be viewed as a movie. The investigation of the Leeds Methane Oxidation Mechanism via element flux analysis, using KINALC and FluxViewer is presented at plug-flow and premixed flame conditions, at several fuel-to-air ratios. Both KINALC and FluxViewer are freely available from Web address: http://garfield.chem.elte.hu/Combustion/Combustion.html
Decomposition of carbon tetrachloride in a RF thermal plasma reactor was investigated in oxygen-argon atmosphere. The net conversion of CCl4 and the main products of decomposition were determined by GC-MS (Gas Chromatographic Mass Spectroscopy) analysis of the exhaust gas. Temperature and flow profiles had been determined in computer simulations and were used for concentration calculations. Concentration profiles of the species along the axis of the reactor were calculated using a newly developed chemical kinetic mechanism, containing 34 species and 134 irreversible reaction steps. Simulations showed that all carbon tetrachloride decomposed within a few microseconds. However, CCl4 was partly recombined from its decomposition products. Calculations predicted 97.9 % net conversion of carbon tetrachloride, which was close to the experimentally determined value of 92.5%. This means that in RF thermal plasma reactor much less CCl4 was reconstructed in oxidative environment than using an oxygen-free mixture, where the net conversion had been determined to be 61%. The kinetic mechanism could be reduced to 55 irreversible reaction steps of 26 species, while the simulated concentrations of the important species were within 0.1% identical compared to that of the complete mechanism.
A regional air quality model has been developed that describes
the transport and chemical transformation of photochemical oxidants
across Central Europe using an adaptive gridding method to achieve high
spatial resolution. High-resolution emission inventories for Budapest and
Hungary were utilised. The air pollution episode in August 1998 was
modelled using a
fixed coarse grid (mesh size 70 km) a fixed fine grid (17.5 km) and an
adaptive, variable sized (from 17.5 to 70 km) grid. The fine and the
adaptive grid models provided similar results, but the latter required 50%
longer computing time. High ozone concentrations appeared downwind of
Budapest and the plume extended up to about 150 km from the city at 17.00
on the simulated day. The simulation results were compared with ozone
concentrations measured at the K-puszta and Hortobágy monitoring stations.
84 A. Lovrics, A. Csikász-Nagy, I. Gy.
Zsély, J. Zádor, T. Turányi, B Novák
Time scale and dimension analysis of
a budding yeast cell cycle model
BMC
Bioinformatics, 7:494(2006)
The progress through the eukaryotic cell division cycle is driven by an
underlying molecular regulatory network. Cell cycle progression can be
considered as a series of irreversible transitions from one steady state
to another in the correct order. Although this view has been put forward
some time ago, it has not been quantitatively proven yet. Bifurcation
analysis of a model for the budding yeast cell cycle has identified only
two different steady states (one for G1 and one for mitosis) using cell
mass as a bifurcation parameter. By analyzing the same model, using
different methods of dynamical systems theory, we provide evidence for
transitions among several different steady states during the budding yeast
cell cycle. By calculating the eigenvalues of the Jacobian of kinetic
differential equations we have determined the stability of the cell cycle
trajectories of the Chen model. Based on the sign of the real part of the
eigenvalues, the cell cycle can be divided into excitation and relaxation
periods. During an excitation period, the cell cycle control system leaves
a formerly stable steady state and, accordingly, excitation periods can be
associated with irreversible cell cycle transitions like START, entry into
mitosis and exit from mitosis. During relaxation periods, the control
system asymptotically approaches the new steady state. We also show that
the dynamical dimension of the Chen’s model fluctuates by increasing
during excitation periods followed by decrease during relaxation periods.
In each relaxation period the dynamical dimension of the model drops to
one, indicating a period where kinetic processes are in steady state and
all concentration changes are driven by the increase of cytoplasmic
growth.We apply two numerical methods, which have not been used to analyze
biological control systems. These methods are more sensitive than the
bifurcation analysis used before because they identify those transitions
between steady states that are not controlled by a bifurcation parameter
(e.g. cell mass). Therefore by applying these tools for a cell cycle
control model, we provide a deeper understanding of the dynamical
transitions in the underlying molecular network.
In the lower troposphere of the Titan the temperature is about 90 K, therefore the chemical production of compounds in the CH4/N2 atmosphere is extremely slow. However, atmospheric electricity could provide conditions at which chemical reactions are fast. This paper is based on the assumption that there are lightning discharges in the Titan's lower atmosphere. The temporal temperature profile of a gas parcel after lightning was calculated at the conditions of 10 km above the Titan's surface. Using this temperature profile, composition of the after-lightning atmosphere was simulated using a detailed chemical kinetic mechanism consisting of 1829 reactions of 185 species. The main reaction paths leading to the products were investigated. The main products of lighting discharges in the Titan's atmosphere are H2, HCN, C2N2, C2H2, C2H4, C2H6, NH3 and H2CN. The annual production of these compounds was estimated in the Titan's atmosphere.
95 T. Kovács, T. Turányi, J.
Szépvölgyi
CCl4 decomposition in RF thermal
plasma in inert and oxidative environments
Plasma Chemistry and Plasma
Processing, , 30,
281-286 (2010)
All uncertainty analysis studies carried out so far on chemical kinetic systems assumed that the uncertainties of the rate coefficients are independent of temperature, which leads to wrong results in varying temperature systems. Most chemical kinetic databases provide the recommended values of the Arrhenius parameters, the temperature range of validity and the temperature dependence of the uncertainty of rate coefficient k. A method is presented for the transformation of the uncertainty of k to the joint probability density function of the Arrhenius parameters, which is needed for a realistic uncertainty analysis in varying temperature chemical kinetic systems. Recommendations are given for an improved representation of the uncertainty information in future chemical kinetic databases.
Chemical kinetics databases for many elementary gas-phase reactions
provide the recommended values of the Arrhenius parameters, the
temperature range of their validity, and the temperature dependence of the
uncertainty of the rate coefficient k.
An analytical expression is derived that describes the temperature
dependence of the uncertainty of k
as a function of the elements of the covariance matrix of the Arrhenius
parameters. Based on this analytical expression, the various descriptions
of the temperature dependence of the uncertainty of k
used in the combustion, and in the IUPAC and JPL atmospheric chemical
databases are analyzed in detail. Recommendations are given for an
improved representation of the uncertainty information in future chemical
kinetics databases using the covariance matrix of the Arrhenius
parameters. Utilization of the joint uncertainty of the Arrhenius
parameters is needed for a correct uncertainty analysis in varying
temperature chemical kinetic systems. A method is suggested for the
determination of the covariance matrix and the joint probability
density function of the Arrhenius parameters from the present uncertainty
information given in the kinetics databases. The method is demonstrated on
seven gas kinetic reactions exhibiting different types of uncertainty
representation
The temperature dependence of rate coefficient k
is usually described by the Arrhenius expression ln k =
ln A -
(E/R) T-1. Chemical kinetics databases contain the recommended values
of Arrhenius parameters A and E, the
uncertainty parameter f(T) of the rate
coefficient and temperature range of validity of this information.
Taking ln k as a random variable with known normal
distribution at two temperatures, the corresponding uncertainty of ln k at other temperatures was calculated. An algorithm is
provided for the generation of the histogram of the transformed
Arrhenius parameters ln A and E/R, which is in accordance with their 2D
normal probability density function (pdf). The upper and the
lower edges of the 1D normal distribution of ln k correspond to
the two opposite edge regions of the 2D pdf of the transformed
Arrhenius parameters. Changing the temperature, these edge regions move
around the 2D cone. The rate parameters and uncertainty data belonging
to reactions H+H2O2=HO2+H2
and O+HO2=OH+O2 were used as examples.
The
misunderstandings related to thermodynamics (including chemical
equilibrium) and chemical kinetics of first and second year Hungarian
students of chemistry, environmental science, biology and pharmacy were
investigated. We demonstrated that Hungarian university students have
similar misunderstandings in physical chemistry to those reported in
published research papers. We also found that there are significant
differences between the misunderstandings in physical chemistry of the
students who have had very different levels of chemistry studies at the
university. However, there is no significant difference between the four
students’ groups in misunderstandings brought from the secondary
education. Behind the students’ misunderstandings found in this survey
there are some common reasons, like using everyday analogy in solving
scientific problems, assuming macroscopic properties at particulate
level, reducing proportionality to direct proportionality, and mixing
the concepts of thermodynamics and reaction kinetics.
The chemical
kinetic measurements can be categorised as direct and indirect ones.
In direct measurements, the reaction conditions are selected in such a
way that the measured signal depends mainly on the rate parameters of
a single reaction step, thus a rate coefficient can be determined from
it directly. In the indirect measurements, the experimental results
depend on the rate parameters of several elementary reactions and
these data can be interpreted via simulations using a reaction
mechanism. Assignation of rate parameters of detailed reaction
mechanisms is usually based on direct kinetic measurements and the
performance of the mechanism is checked on the basis of the results of
indirect measurements. However, the rate coefficients determined in
direct measurements have large uncertainty (typically factor of 1.3 to
3.0), usually the first version of a detailed reaction mechanism do
not reproduce the indirect measurements. Therefore, most published
mechanisms contain tuned rate parameters that were selected almost
arbitrarily. In an alternative approach, developed and applied by
Frenklach et al. and Wang et al.,
the values of the most critical rate parameters are determined on the
basis of selected indirect measurements.
A new method was suggested recently by our Laboratory that consists of
the following main steps.
(i) Indirect measurements belonging to the chemical system to be
investigated are selected.
(ii) The sensitivities of the simulated values corresponding to the
measured signal in the indirect experiments with respect to the rate
parameters are calculated. This sensitivity analysis allows the
identification of the rate parameters to be optimized. Experimental
rate coefficient values determined in direct experiments belonging to
the highly sensitive reactions are collected.
(iii) The domain of uncertainty of the rate parameters is determined
via a literature review. For the Arrhenius parameters, this
determination is based on the relation between the temperature
dependent uncertainty of the rate coefficient and the temperature
independent uncertainty of the corresponding Arrhenius parameters.
(iv) The optimized values of the rate parameters of the selected
elementary reactions within their domain of uncertainty are determined
using a newly developed global nonlinear fitting procedure. The
optimized rate parameters may include not only Arrhenius parameters,
but also third-body efficiencies, enthalpies-of-formation, parameters
of pressure dependence, etc.
(v) The covariance matrix of all fitted parameters is calculated. This
covariance matrix is transformed to the uncertainty parameter f
for each important reaction. Application of uncertainty parameter f is traditional for the characterization of the
temperature dependence of the uncertainty of a rate coefficient in gas
kinetics.
A series of tools and methods is recommended for the chemical kinetics interpretation of combustion related experimental data. These data can be directly measured rate coefficients of elementary reactions at a given temperature, pressure and bath gas, or results of indirect measurements, like ignition delay time measurements in shock tubes or rapid compression machines, laminar burning velocity measurements, or concentration profile determinations in various reactors. The data are suggested to be stored in ReSpecTh Kinetics Data format files, which is an extension of the PrIMe data format, allowing software independent and permanent storage. Important model parameters related to the various indirect measurements are identified using local sensitivity analysis. Prior uncertainty bands of the important rate parameters are determined based on direct measurements and theoretical calculations. The temperature dependent uncertainty bands of the rate coefficients can be converted to the uncertainty domain of the Arrhenius parameters. All important rate parameters are fitted in one step within their domain of prior uncertainty using a global optimization method, taking into account all relevant indirect and direct measurements. This approach provides the best estimated values of the important parameters that can be obtained from the experimental data considered, and also their covariance matrix, which is a representation of their joint posterior uncertainty. Applications of this methodology are presented for the interpretation of several series of measurement data, and also for the optimization of the combustion mechanisms of fuels like hydrogen, syngas, methanol and ethanol.
The experiments of Rahinov et al. (Combust. Flame, 145 (2006) 105-116) measuring NH2 concentration profiles in methane?air laminar flat flames doped with ammonia were re-evaluated. The flames were simulated with the FlameMaster code using a modified POLIMI NOx mechanism. Based on local sensitivity analysis results, Arrhenius parameters A, n, E of reaction steps NH2+H = NH+H2 and NH3+OH = NH2+H2O were selected for optimization, which took into account not only the experimental data of Rahinov et al., but also related direct measurements and theoretical determinations as optimization targets. The optimized mechanism described the measured concentration profiles better than the original one, while the new rate parameter values were within the prior uncertainty limits obtained from the evaluation of literature data
139 H. Böttler, C. Olm, T. Varga, S. Hartl, M. Pollack, C. Hasse, T. Turányi
Assessment of Reaction Mechanisms Using a Large Set of Butanol Combustion DataButanol is a promising alternative biofuel and it has received considerable scienti?c interest in the recent years. It can be used in gasoline-fuelled IC engines at much higher mixture fractions than ethanol without the need for fur-ther modi?cations of the engine. A large amount of ignition delay time (127 datasets), laminar burning velocity (43 datasets) and speciation measurements (78 datasets) for butanol combustion was collected from the literature; these 7074 data points cover a wide range of conditions. FlameMaster simulations were performed with 9 published reaction mechanisms. The performance of each mechanism was analysed at the experimental conditions to identify their strengths and weaknesses.
Applications of global uncertainty methods for models with
correlated parameters are essential to investigate chemical kinetics
models. A global sensitivity analysis method is presented that is able
to handle correlated parameter sets. It is based on the coupling of the
Rosenblatt transformation with an optimized Random Sampling High
Dimensional Model Representation (HDMR) method. The accuracy of the
computational method was tested on a series of examples where the
analytical solution was available. The capabilities of the method were
also investigated by exploring the effect of the uncertainty of rate
parameters of a syngas-air combustion mechanism on the calculated
ignition delay times. Most of the parameters have large correlated
sensitivity indices and the correlation between the parameters has a
high influence on the results. It was demonstrated that the values of
the calculated total correlated and final marginal sensitivity indices
are independent of the order of the decorrelation steps. The final
marginal sensitivity indices are meaningful for the investigation of the
chemical significance of the reaction steps. The parameters belonging to
five elementary reactions only, have significant final marginal
sensitivity indices. Local sensitivity indices for correlated parameters
were defined which are the linear equivalents of the global ones. The
results of the global sensitivity analysis were compared with the
corresponding results of local sensitivity analysis for the case of the
syngas-air combustion system. The same set of reactions was indicated to
be important by both approaches.
A re-evaluation of the flow reactor experiments of Abian et al. (Int. J. Chem. Kinet. 2015; 47: 518-532) is presented. In these experiments nitrogen oxide formation was measured at atmospheric pressure in temperature range 1700–1810 K, using several mixtures containing different ratios of oxygen, nitrogen and water vapor. Based on the mechanism of Abian et al., the two most important reaction steps for NO formation (R1: NO + N = N2 + O and R2: N2O + O = 2 NO) were identified by local sensitivity analysis. For the optimization of the Arrhenius parameters of these reaction steps, 25 datapoints measured by Abian et al., two direct rate coefficient measurements (73 data points) and one theoretical calculation were used. The obtained mechanism with the optimized Arrhenius parameters (R1: A = 1.176·1010 cm3mol–1s–1, n = 0.935, E/R = –693.68 K; R2: A = 1.748·1016 cm3mol–1s–1, n = –0.557, E/R = 14447 K) described the results of the flow reactor experiments, direct measurements and theoretical calculations much better compared to the Abian et al. mechanism, and also several recent NOx mechanisms. The rate coefficients of these elementary reactions were obtained with low uncertainty in the temperature range of 1600 K to 2200 K.
Five different numerical frameworks with possibilities of modelling
homogenous batch reactors and laminar premixed flames are compared in
terms of results
consistency and performance. The considered projects are Cantera,
Chemkin-II, Ansys/Chemkin-PRO, FlameMaster, and OpenSMOKE++. In this
study, first,
results for homogenous, isochoric, adiabatic batch reactors are compared
based on test cases precisely defined in terms of numerical setup and
initial conditions. All
frameworks provide consistent results. Based on this agreement, the
comparison is extended for premixed laminar flames. Very good agreement
between Cantera,
Ansys/Chemkin-Pro, FlameMaster, and OpenSMOKE++ is achieved given that the
same modelling assumptions and a sufficiently accurate numerical setup are
chosen
by the user. Finally, Cantera, FlameMaster, and OpenSMOKE++ are compared
in a process time benchmark for homogenous, isochoric batch reactors.
The combustion chemistry of butanol, a promising alternative biofuel, is not fully understood yet. A comprehensive set of experimental data for butanol isomers was collected and their simulation was carried out with eighteen butanol mechanisms. The performance of the mechanisms was measured and compared based on a sum-of-square error function that characterized the agreement between the experimental and the simulation data. In general, none of the reaction mechanisms could describe the combustion of all four butanol isomers in all types of experiments consistently well. Mechanism by Sarathy et al. (2014) seemed to be the most predictive.
Methane is the major component of natural gas, which is one of the most
widely used fuels. Large amount of shock tube (ST) and rapid compression
machine (RCM) ignition delay measurements are available for validating
detailed mechanisms. For a quantitative assessment of methane combustion
modelling, a least squares function is used here to show the agreement
between measurements and simulations. Caltech-2015, Aramco_II-2016, and
Glarborg-2018 were proved to be the most accurate mechanisms for the
simulation of methane combustion at ST experimental conditions, while
AramcoII-2016 has the lowest prediction error at RCM conditions.
A mechanism for the description of the H2/O2/NOx
combustion systems was optimized via the method developed in our
laboratory using computer framework code Optima++. In total, 5073
experimental data points (ignition delay times, concentration profiles and
burning velocity measurements) were collected from the literature and were
reproduced using 17 recent NOx mechanisms. The performance of the
Glarborg-2018 mechanism was the best. Ten elementary reactions were
selected based on local sensitivity analysis and the Arrhenius parameters
of them were fitted to indirect experimental data, and direct experimental
and theoretical determinations of the rate coefficients. This way more
accurate rate parameters of these reactions were obtained and the
temperature dependent uncertainties of the rate coefficients were
calculated.
In the last two years, three comprehensive reaction mechanisms were published, which can be used to simulate NOx formation during syngas combustion. The aim of this work is to investigate the performances of these mechanisms at various experimental conditions. The mechanisms of Zhang et al. and Glarborg et al. provided somewhat better results than the POLIMI_2018 mechanism. The HOCO chemistry and the importance of reaction N2O + H2 = N2 + H2O were also investigated.
The low-temperature first ignition of n-butane/air mixtures is studied in this work, using a short chemistry model with all the important isomers. The reaction rates were obtained from published data. The first ignition delay time and the overall heat release (temperature jump) were obtained analytically in closed form, where the parametric influence can be easily seen. The chain branching leading to a thermal runaway is produced by a competition in the decomposition of the butylperoxy radicals, RO2i=pC4H9O2 and sC4H9O2. The heat released by the low temperature kinetics is able to increase the temperature to high values, greater than the crossover temperature.
Literature experimental data were collected about hydrogen-oxygen
combustion systems doped with NO, NO2 or N2O or
about H2/N2O combustion systems. The data included
ignition delay times, laminar burning velocities, and concentrations
measured in flow reactors, JSRs and burner stabilized flames. In total,
4949 data points in 207 data sets from 35 publications were used. These
experimental data were reproduced using sixteen NOx mechanisms. The
performance of the Nakamura-2017, Glarborg-2018 and Zhang-2017 mechanisms
were the best. Nine elementary reactions were selected from the
Glarborg-2018 mechanism based on sensitivity analysis and the Arrhenius
parameters (A, n, E) of these reactions were fitted not only to the
indirect experimental data, but also direct experimental and theoretical
determinations of the rate coefficients. This way more accurate rate
parameters of these reactions could be obtained and the temperature
dependent uncertainty of the rate coefficients was calculated. The
Glarborg-2018 mechanism modified with the optimized rate parameters
described the experimental data better than any other investigated
reaction mechanism.
Ammonia is a potential fuel for the storage of thermal energy. Experimental data were collected for homogeneous ammonia combustion: ignition delay times measured in shock tubes (247 data points in 28 datasets from 4 publications) and species concentration measurements from flow reactors (194/22/4). The measurements cover wide ranges of temperature T, pressure p, equivalence ratio φ and dilution. The experimental data were encoded in ReSpecTh Kinetics Data Format version 2.2 XML files. The standard deviations of the experimental datasets used were determined based on the experimental errors reported in the publications and also on error estimations obtained using program MinimalSplineFit. Simulations were carried out with eight recently published mechanisms at the conditions of these experiments using the Optima++ framework code, and the FlameMaster and OpenSmoke++ solver packages. The performance of the mechanisms was compared using a sum-of-square error function to quantify the agreement between the simulations and the experimental data. Ignition delay times were well reproduced by five mechanisms, the best ones were Glarborg-2018 and Shrestha-2018. None of the mechanisms were able to reproduce well the profiles of NO, N2O and NH3 concentrations measured in flow reactors.
In chemical kinetics, the reaction rate coefficients characterize the
speed of a chemical reaction. The temperature dependence of the rate
coefficients can be defined by Arrhenius parameters. The values of these
parameters have been determined in experiments or theoretical studies,
therefore their values are uncertain. In the kinetics databases the
uncertainty parameter of the rate coefficient is usually considered to be
temperature independent. Calculation of temperature dependent uncertainty
limits of rate coefficients of elementary reactions in such a way that
these limits are consistent with the temperature dependence of the rate
coefficient is necessarry for further model developments and
investigations.
The performance of 17 recent detailed reaction mechanisms describing the interactions of methanol and formaldehyde with nitrogen oxides in combustion systems was investigated based on large number of literature experimental data covering a wide range of conditions. This data collection consists of 2552 data points of concentration profiles in 243 datasets measured in jet stirred reactors, tubular flow reactors and shock tubes. The two best mechanisms were found to be the Shrestha-2019 and Glarborg-2018 mechanisms, which were selected for further investigations. Two additional mechanisms were created via the replacement of the hydrogen, syngas, methanol submechanisms, and the parameters of nine N/H/O reactions to ones from our previous mechanism optimization studies. Local sensitivity analysis of the kinetic and thermodynamic parameters (Arrhenius A-factors, heat capacities, standard enthalpies of formation and standard molar entropies) of these four mechanisms were carried out. The results were in good agreement and the most sensitive reactions belong to the neat hydrogen, syngas, or methanol oxidation. The most important reactions of the interaction between C1 species and NOx are hydrogen-abstraction reactions CH3OH + NO2 = HONO + CH2OH and CH2O + NO2 = HONO + HCO. The most sensitive thermodynamic properties are the molar heat capacities of species OH, NO, HONO and NO2, and the standard enthalpies of formation and entropies of these species have also significant sensitivities. According to the local uncertainty analysis of the kinetic and thermodynamic parameters, the rate coefficients of the NOx chemistry have the highest contribution to the overall uncertainty of the simulation results, especially those of the two reactions above. The highest uncertainty caused by the thermodynamic parameters is due to the heat capacity of HNO, OH, HO2 and NO2 and some other species while the uncertainty contributions of all enthalpies of formation and entropies were negligible.
153 Tibor Nagy, Tamás Turányi
Minimal Spline
Fit: a model-free method for determining statistical noise of experimental
data series
Proceedings of the European Combustion Meeting – 2021, Paper 336,
14-15 April, 2021, Naples, Italy
Robust and accurate chemical kinetics models of low uncertainty are required to aid the development of novel combustion devices using simulations. Parameter optimization against experimental data is a possible way to develop such models. A proper objective function that can handle reference data of different types and magnitudes is obtained by normalizing the deviations by the corresponding experimental error. We propose a novel model-free method and a corresponding code, called Minimal Spline Fit, to estimate the statistical noise of experimental data series and to predict its noise-free profile.
154 Márton Kovács, Tibor Nagy, Tamás Turányi
Investigating novel strategies for parameter optimization on a
methanol/NOx combustion mechanism
Proceedings of the European Combustion Meeting – 2021, Paper 337,
14-15 April, 2021, Naples, Italy
Local sensitivity coefficients and parameter uncertainties are the usual measures used for selecting parameters for the optimization of combustion kinetic models. We identified two further factors and construct four novel measures for parameter ranking and benchmarked them against two known measures in a 10-parameter hierarchical optimization of a methanol/NOx mechanism on a large experimental data set. It was found that measures that did not incorporate uncertainty information could reduce the error function initially the most steeply, but in the long run the other methods performed better, though similarly. Regarding posterior uncertainties, one of the novel strategies based on error function derivative and uncertainty information performed the most reliably and can be recommended for future use.
Methane is the major component of natural gas, which is one of the most widely used fuels. Large amount of shock tube (ST) and rapid compression machine (RCM) ignition delay measurements are available in the literature for validating its detailed combustion mechanisms. A large set of experimental data was collected for methane combustion: ignition studies in STs (4939 data points in 574 datasets) and in RCMs (582/69). In total, 5521 data points in 643 datasets from 76 publications were collected covering wide ranges of temperature T, pressure p, equivalence ratio φ and diluent concentration. For a quantitative assessment of methane combustion models, a least-squares-function is used to show the agreement between measurements and simulations. 13 recent methane combustion mechanisms were tested against these experimental data, and the dependence of their predictions on the types of experiments and the various experimental conditions was investigated. The mechanism comparison results show that most mechanisms could reproduce well the experimental ignition delay times (IDTs) measured in STs. IDTs measured in RCMs and STs at low temperatures (below 1000 K) could also be well predicted by several mechanisms. SanDiego-2014, Caltech-2015, Aramco-II-2016 and Glarborg-2018 were found to be the most accurate mechanisms for the simulation of methane combustion under ST experimental conditions, while Aramco-II-2016 had the smallest prediction error under RCM conditions. Local sensitivity analysis was carried out to determine the effect of reactions on the simulation results obtained under given experimental conditions and to identify the critical reaction steps for improving the methane combustion models.
156 Éva Valkó, Máté Papp, Márton Kovács,
Tamás Varga, István Gy. Zsély, Tibor Nagy, Tamás Turányi
Design of
combustion experiments using differential entropy
Combustion
Theory Modelling, 26, 67-90 (2022)
The aim of several combustion experiments is the determination of the
rate coefficients of important elementary reactions. The experimental
conditions are usually selected on the basis of local sensitivity
analysis. Shock tube and tubular flow reactor experiments are often
designed in such a way that only one reaction step is important at the
investigated conditions. Sheen and Manion (J. Phys. Chem. A, 118
(2014) 4929–4941) suggested a method for the design of shock tube
experiments based on differential entropy. Their method was modified and
extended in this work. In the extended method, both the experimental and
residual errors of the measurements are considered at the calculation of
the posterior uncertainty of the determined rate parameters, the
differential entropy matrix is calculated in an analytical way, and the
net information flux value is calculated for each suggested experimental
point. In an iterative procedure, all investigated experimental points
with negative net information flux values are discarded and the remaining
experimental conditions are recommended for the measurements. The most
valuable candidate experimental points can be determined based on the net
information flux values. The method was used for the selection of
experimental conditions for the determination of the rate coefficient of
reaction NO2+H = NO+OH at conditions similar to the tubular
flow reactor experiments of Alzueta et al. (Energy Fuels, 15
(2001) 724–729). In these experiments the oxidation of methanol was
investigated with and without NO addition. Our method suggested a range of
temperature, equivalence ratio and initial NO concentration, where the
experimental data carry the most information on the rate coefficient of
this elementary reaction.
Large amount of experimental data for laminar burning velocity (LBV)
measurements of methane (+ H2/CO) - oxygen - diluent mixtures
(5500 data points in 646 datasets) covering wide ranges of equivalence
ratio, diluent ratio, cold side temperature and pressure were collected
from 111 publications. The diluents included N2, H2O,
CO2, Ar and He. The data files are available on the ReSpecTh
site (http://respecth.hu). Performances of 12 methane combustion
mechanisms on reproducing these LBV measurements were analyzed according
to experiment types and conditions. Most mechanisms could predict well the
LBVs for stoichiometric and fuel-lean mixtures and for diluent ratios
higher than 60%. The performances of several mechanisms were relatively
poor at other conditions. Focusing on the operating conditions of natural
gas engines, we recommend the application of mechanisms FFCM-I-2016,
SanDiego-2014, and NUIG1.1-2021 for engine simulations. Mechanisms
Aramco-II-2016, Konnov-2009, Caltech-2015 and Glarborg-2018 have the
lowest average errors for the reproduction of all available methane LBV
data. Using local sensitivity analysis on the most accurate mechanisms, we
identified 29 important elementary reactions, which, however, were not
present in all the 12 mechanisms. We also collected large amount of
directly measured and theoretically calculated rate coefficients for these
reactions and compared them with the rate coefficients used in the 12
mechanisms. Reactions found important in any of the Aramco-II-2016,
Konnov-2009 and Glarborg-2018 mechanisms, but missing from the
Aramco-II-2016, Konnov-2009, Glarborg-2018, Caltech-2015, FFCM-I-2016 and
NUIG1.1-2021 mechanisms were added to these six mechanisms to investigate
if the extended mechanism performs better than the original one. Some of
the extended mechanisms became the best performing mechanisms.
An experimental and kinetic study on pyrolysis and oxidation of a real light naphtha fuel and its surrogate blend were conducted. Based on the chemical functional group method, a three-component surrogate blend for the target naphtha was formulated, which contains 64.2 mol% iso-pentane, 21.0 mol% n-hexane, and 14.8 mol% methylcyclopentane. The pyrolysis and oxidation characteristics of the target naphtha fuel and the formulated surrogate were compared using a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of the three components, oxygen, hydrogen, CO, CO2, and C1-C4 hydrocarbons were measured by gas chromatograph. Similar global reactivities between the two test fuels were observed in both pyrolysis and oxidation experiments. In addition, a detailed chemical kinetic model was constructed and validated against the species mole fraction profiles measured in JSR experiments. The present model can provide reasonable prediction of the experimental measurements of the species mole fractions in pyrolysis and oxidation of the surrogate blend. Uncertainty-weighted sensitivity analysis indicates that the model prediction of the consumption of the three components of the surrogate blend in pyrolysis are dominated by the rate constants for H-abstraction reactions of isopentane, n-hexane, methylcyclopentane and propene by H atom and methyl radical. The model predictions of the oxidation reactivity of the surrogate blend mainly depend on H-abstraction reactions from the three surrogate components by HO2 radical at 800 K, while the H-abstraction reactions from aldehyde and alkene intermediates become more significant at 950 K.
159 Csanád Kalmár, Tamás Turányi, István
Gy. Zsély, Máté Papp, Ferenc Hegedűs
The importance of chemical mechanisms in sonochemical modelling
Ultrasonics
Sonochemistry, 83, 105925 (2022)
A state-of-the-art chemical mechanism is introduced to properly describe
chemical processes inside a harmonically excited spherical bubble placed
in water and saturated with oxygen. The model uses up-to-date
Arrhenius-constants, collision efficiency factors and takes into account
the pressure-dependency of the reactions. Duplicated reactions are also
applied, and the backward reactions rates are calculated via suitable
thermodynamic equilibrium conditions. Our proposed reaction mechanism is
compared to three other chemical models that are widely applied in
sonochemistry and lack most of the aforementioned modelling issues. In the
governing equations, only the reaction mechanisms are compared, all other
parts of the models are identical. The chemical yields obtained by the
different modelling techniques are taken at the maximum expansion of the
bubble. A brief parameter study is made with different pressure amplitudes
and driving frequencies at two equilibrium bubble sizes. The results show
that due to the defficiencies of the former reaction mechanisms employed
in the sonochemical literature, several orders of magnitude differences of
the chemical yields can be observed. In addition, the trends along a
control parameter can also have dissimilar characteristics that might lead
to false optimal operating conditions. Consequently, an up-to-date and
accurate chemical model is crucial to make qualitatively and
quantitatively correct conclusions in sonochemistry.
160 Éva Valkó, Máté Papp, Peng Zhang, Tamás
Turányi
Identification of homogeneous chemical kinetic regimes of methane-air
ignition
. Proc. Combust.
Inst., 39, 467-476 (2023)
Sensitivity analysis results for ignition delay time (IDT) may be very different depending on the initial temperature, pressure and equivalence ratio φ, but similar in some regions of these variables. This phenomenon was investigated systematically by carrying out ignition simulations and local sensitivity calculations of methane-air mixtures using the Aramco-II-2016 mechanism at 14417 combinations of initial temperature (changed between 500 K and 3000 K), initial pressure (0.05-500 atm) and φ (0.05-8.0) values. The cluster analysis of the sensitivity vectors identified five large kinetically homogeneous regions. Each region has well defined borders in the (T, p, φ) space and can be characterized by different sets of important reactions. The related kinetic scheme is very different in each region. Regions 1 and 2 are dominated by catalytic cycles based on species CH3O2/CH3O2H and HO2/H2O2/CH3O, respectively. In regions 3, 4, and 5 the H atoms are converted to CH3 in an identical chain branching sequence, but the back conversion is via three different routes. Literature experimental data on the IDTs of methane-air mixtures were sorted according to these five regions. Regions 1 to 5 contain 214, 328, 3, 0, and 237 experimental data points, respectively. In regions 1, 2 and 5 the data points are well reproduced by the Aramco-II-2016 mechanism, but little or no experimental information is available about kinetic regions 3 and 4. Further experimental exploration of the ignition of methane-air mixtures may aim the study of these regions. A similar approach can be used for the characterization of other combustion systems and sorting the related experimental data.
161 Márton Kovács, Máté Papp, Tamás
Turányi, Tibor Nagy
A novel active parameter selection strategy for the efficient optimization
of combustion mechanisms
Proc. Combust. Inst., 39, 5259-5267 (2023)
Optimization of large combustion mechanisms means that a few dozen
parameters (called active parameters) are optimized within their
uncertainty limits to achieve a better reproduction of the experimental
data, which is usually measured by a mean square error function. In
previous studies, the active parameters were selected based either on
their local sensitivity coefficients (strategy S) or on the products of
local sensitivity coefficient and a corresponding uncertainty parameter
(strategy SU). This latter measure is known by various names: optimization
potential, sensitivity-uncertainty index or uncertainty-weighted
sensitivity coefficient. In this work, we proposed three novel active
parameter selection strategies of increasing complexity (PCA-SU, PCA-SUE,
PCALIN) and demonstrated their superior performance in the optimization of
pre-exponential factors (A) in a methanol/NOx combustion mechanism (562
reaction steps of 70 species) against 2360 data measured in shock tube,
JSR and flow reactor experiments. The novel methods are based on the
principal component analysis (PCA) of sensitivity matrices scaled by the
uncertainties of parameters (U) and the uncertainty of the experimental
data (E). These PCA-based methods take into account parameter correlations
and designate parameters groups and corresponding relevant subsets of
experimental data, thereby a factor of 4-7 savings in optimization time
was achieved over the S and SU methods. PCA-SUE method performed better
than the PCA-SU as it also considered the uncertainty of the experimental
data. The PCALIN strategy is similar to PCA-SUE, but it also considers the
linear change (LIN) of the error function, which depends on the simulation
error of experimental data, and thereby it could provide the most accurate
models as a function of the number of active parameters. Based on the
PCALIN strategy, fitting all three Arrhenius parameters resulted in
further improvements, however, it provided moderate improvements over
simple A-factor tuning and required significantly more computer time.
Optimization of detailed combustion mechanisms means that the
corresponding kinetic model is fitted to experimental data via optimizing
their important rate and thermodynamic parameters within their domain of
uncertainty. Typically, several dozen parameters are fitted to several
hundred to several thousand data points. Many numerical optimization
methods have been used, but the efficiency of these methods has not been
compared systematically. In this work, parameters of a H2/O2/NOx
mechanism (214 reaction steps of 35 species) were fitted to 1552 indirect
(ignition delay times measured in shock tubes and concentrations measured
in flow reactors) and 755 direct measurements. Three test cases were
investigated: (1) fitting the Arrhenius parameters of 2 reaction steps to
732 data points; (2) fitting the Arrhenius parameters of 4 reaction steps
to 1077 data points; (3) fitting the Arrhenius parameters of 10 reaction
steps to 2307 data points. All three cases were investigated in two ways:
fitting the A-parameters only and fitting all Arrhenius parameters (5, 11
and 29 parameters, respectively). A series of global (FOCTOPUS, genetic
algorithm, simulated annealing, particle swarm optimization, covariance
matrix adaptation evolutionary strategy (CMA-ES)) and local (simplex,
pattern search, interior-point, quasi-Newton, BOBYQA, NEWUOA) optimization
methods were tested on these cases, some of them in two variants. The
methods were compared in terms of the final error function value and
number of error function evaluations. The main conclusions are that the
FOCTOPUS resulted in the lowest final error value in all cases, but this
method required relatively many error function evaluations. As the task
became more difficult, more and more methods failed. A variant of the
BOBYQA method looked stable and efficient in all cases.
This chapter introduces state-of-the-art modelling techniques of chemical kinetics inside a single spherical oscillating bubble placed in an infinite domain of liquid water. The initial content of the bubble is pure oxygen and water vapor. The reaction mechanism that governs chemical kinetics inside the bubble takes into account many aspects that are usually neglected in previous sonochemical investigations. First, at the collapse state of a bubble, the pressure inside can reach several hundreds of atmospheres; thus, the incorporation of the pressure dependence of reactions in which a third body plays a role is mandatory. Second, third body efficiencies are also taken into account. Third, the backward reactions are computed via thermodynamic equilibrium conditions. Fourth, reactions that have non-Arrhenius temperature dependence can be described by two sets of Arrhenius constants. These reactions are identified and modelled properly. As more experimental data have been accumulated over the decades, the Arrhenius constants of certain reactions have been changed even by orders of magnitude. Therefore, it is also important to employ up-to-date values of the Arrhenius constants. The behavior of the proposed model is demonstrated with reaction condition sets (pressure amplitude, frequency and bubble size) typically used during the experiments. The production of important chemical species (e.g., hydrogen or free radicals) are investigated from energy efficiency points of view (yield in mole per unit dissipated power of the bubble).
A detailed review of the performances of 24 butanol combustion mechanisms, published between 2008 and 2020, is given using a comprehensive experimental data collection (89388 data points in 266 datasets from 32 publications). The data cover wide ranges of equivalence ratio (phi = 0.38 – 2.67), diluent ratio (0.15 – 0.98), initial temperature (672 K – 1886 K) and pressure (0.9 atm – 90 atm). The collection includes ignition delay time measurements in shock tubes and rapid compression machines, concentration determinations in shock tubes, jet-stirred reactors, flow reactors, and laminar burning velocity measurements. The experimental data were recorded in Respecth Kinetics Data Format (RKD format) v.2.3 XML data files, which are available in the ReSpecTh site (http://respecth.hu). The standard deviations of the measurements were estimated using both the published experimental uncertainty and the scatter error of the datasets determined by code Minimal Spline Fit. Mechanism CRECK 2020 was found to be the best mechanism for n-butanol (biobutanol) combustion, while mechanisms Sarathy 2014, Vasu 2013, and Yasunaga 2012 (in this order) were the best considering the experimental data for all isomers. A part of the simulations failed, and to improve the ratio of successful simulations code ThermCheck was created, which detects discontinuities and non-smoothness of thermodynamic functions defined by NASA polynomials provided with the published mechanisms and corrects them by tuning their coefficients. Local sensitivity analysis applied at the experimental conditions was used to identify the most important reaction steps of mechanism Sarathy 2014. The sensitivity analysis was extended to the adiabatic ignition of n-butanolair mixtures by systematically changing the initial temperature and pressure. All butanol combustion mechanisms were also tested on a hydrogen combustion data collection, which indicated that some of them were inaccurate due to their inadequate hydrogen combustion reaction block. Suggestions were given for the improvement of the Sarathy 2014 mechanism.
165 Simret Goitom, Tamás Turányi and Tibor Nagy
Testing
various numerical optimization methods on a series of artificial test
functions
Annales
Univ. Sci. Budapest., Sect. Comp., 53 , 175–199 (2022)
Features of several well-known global and local optimization methods were
discussed and their robustness and efficiency were tested on several
artificial test functions in Matlab environment. The tested local methods
were the interior-point, the quasi-Newton method, Nelder-Mead simplex, the
pattern search, the BOBYQA and the NEWUOA methods. The global methods were
the genetic algorithm (GA), the simulated annealing (SA), the particle
swarm optimization (PSO), and the covariance matrix adaptation
evolutionary strategy (CMA-ES) methods. Furthermore, a novel global
optimization method, called FOCusing robusT Optimization with
Uncertainty-based Sampling (FOCTOPUS), which proved to be very efficient
in the optimization of constrained and highly correlated parameters of
combustion kinetic models, was also tested. The test functions were
selected in such a way that they had a variety of features: uni-modal and
multi-modal, differentiable and non-differentiable, separable and
non-separable, low dimensional and high dimensional. The following test
functions were used: 20D Zakharov function, 5D Rosenbrock function, 4D
modified Rosenbrock function, Holder table 2D function, 4D Ackley
function, Cross-in-tray 2D function, 5D Rastrigin function, 20D Alpine
function, typical 2D multi-modal function and the Hartmann-6D function.
The general conclusion here is that, the global methods performed well in
the multi-modal and high-dimensional test functions while the local
methods were superior in the case of low-dimensional and uni-modal test
functions. For the highly multi-modal test functions, the GA was better
than all the other methods. The FOCTOPUS method proved to be inferior to
GA for most of the test functions, thus its application cannot be
generally recommended.
166 András Szanthoffer, István Gyula Zsély,
László Kawka, Máté Papp, Tamás Turányi
Testing of NH3/H2
and NH3/syngas combustion mechanisms using a large amount of
experimental data
Applications in
Energy and Combustion Science (AECS), 14,
100127 (2023)
A possible solution to improve the combustion properties of ammonia is to blend it with other fuels. Two of the most usually used co‑fuels are hydrogen and syngas (H2/CO). To investigate the chemistry of the co-combustion with these fuels, a large amount of indirect experimental data for the combustion of neat NH3, and NH3/H2 and NH3/syngas fuel mixtures were collected from the literature including ignition delay times measured in shock tubes, concentration measurements in jet stirred and flow reactors, and laminar burning velocity measurements. Altogether, 4898 data points (in 472 data series) were recorded which cover wide ranges of equivalence ratio, temperature, and pressure. These experimental data are available in data files in the ReSpecTh site (http://respecth.hu). The performances of 18 recently published detailed reaction mechanisms were quantitatively assessed using the collected experiments. There are significant differences between the performances of the models, and the performance of a mechanism may also vary significantly with the different types of experiments. The best‑performing mechanisms are POLIMI‑2020, KAUST‑2021, and Otomo‑2018 for NH3/H2 fuel mixtures, and Shrestha‑2021, Mei‑2021, and Mei‑2020 for NH3/syngas systems. The results indicate that further mechanism development is needed to reproduce the measurements more accurately. Local sensitivity analysis was carried out on the kinetic and thermodynamic parameters of the best‑performing mechanisms. Even though the investigated models have different parameter sets, the most important reactions and thermodynamic properties are similar. The most important reactions are not the same for the different types of experiments but most of them include the NH3, NH2, and/or NNH species. Among the thermodynamic parameters, model outputs are most sensitive to the data of NH3 and NH2.
167 Tamás Turányi
Reaction kinetics of
hydrogen combustion
Chapter 2 in book:
Hydrogen for future thermal engines, (ed: Efstathios - Alexandros Tingas),
Springer Nature, 2023
https://doi.org/10.1007/978-3-031-28412-0_2
The reaction kinetics of hydrogen combustion was intensively studied already in the first half of the 20th century. The first, second and third explosion limits were discovered, and mechanistic explanations were given. However, fine details of the reaction mechanism and the exact rate parameters are still not known. New reaction steps were proposed even in the last few years. The explosive – non-explosive regions are separated by an inverted S-shape curve in the T – p plane. The backbone of the curve is approximately equal to the line where the rates of reactions H+O2 = OH+O and H+O2+M = HO2+M are equal. The regions of strong and weak explosions are below and above the backbone line, and these regions are dominated by H/O/OH and HO2/H2O2 catalytic cycles, respectively. In a small vessel, the adsorption of radicals HO2 and H form the upper and lower branches of the curve, respectively. All qualitative features of the hydrogen combustion system can be explained by a 10-step mechanism. Several web sites are recommended here which contain comprehensive collections of recent hydrogen combustion mechanisms, direct and indirect experimental data, and theoretical determinations.
The combustion properties of hydrogen-containing fuel mixtures and the effect of the variation of the oxygen content of the oxidizer are at the center of recent research interest. Laminar burning velocity measurements with varied oxygen content can help in the validation of reaction mechanisms for better simulations of combustion systems using exhaust gas recirculation (EGR) or oxygen-enriched atmosphere. Such measurements were carried out in hydrogen-enriched methane-air flames using the heat flux method with higher accuracy and a wider range of initial oxygen and hydrogen concentrations compared to the similar studies in the literature. The mole fractions of the hydrogen and oxygen contents of the initial fuel and oxidizer mixtures were varied between xH2 = 0 and 0.20, and xO2 = 0.14 and 0.23, respectively. The initial gas temperature and pressure were 298 K and 1 bar, respectively. It is demonstrated that the increase of combustion rate by the hydrogen enrichment can be compensated with the decrease of the oxygen content. This compensating effect was investigated in detail in a wide range of equivalence ratio (φ). The experimental data were simulated with 11 widely used methane combustion reaction mechanisms. The prediction accuracies of the mechanisms at lean and rich equivalence ratios were significantly different and the important reaction steps were identified using sensitivity analysis for three mechanisms. Mechanisms POLIMI-2014 and Caltech-2015 gave the best overall predictions.
Comparison of the
performance of ethylene combustion mechanisms
Combust. Flame, 260,
113201 (2024)
Ethylene is a key intermediate in the combustion and pyrolysis of larger
hydrocarbons. A large set of literature experimental data covering wide
ranges of conditions on ethylene combustion was collected: ignition delay
times measured in shock tubes (1160 data points in 114 data series) and
rapid compression machines (83/5); concentration measurements carried out
in jet-stirred reactors (1586/157) and flow reactors (649/59); and laminar
burning velocities (882/59). 14 detailed reaction mechanisms were
investigated using the collected experimental data. The results show
significant differences between the performances of the various
mechanisms. The four best-performing mechanisms are Aramco-2.0-2016,
Aramco-3.0-2018, Yang-2020 and NUIGMech-1.1-2020 based on all included
experimental data. The best-performing model Aramco-2.0-2016 was further
investigated by local sensitivity analysis. Several reaction steps were
found to be important for simulating the experiments: many reactions of
the hydrogen, syngas and C1 hydrocarbons oxidation systems, furthermore
reactions C2H3+O2=CH2CHO+O and
C2H4+OH=C2H3+H2O
which are specific for ethylene combustion.
.
This study aims to assess the performances of 18 detailed reaction
mechanisms quantitatively using a large amount of experimental data on the
combustion of NH3/H2 fuel mixtures. For this purpose, 3,770 experimental
data points obtained in shock tube ignition delay time, jet stirred and
flow reactor concentration, and laminar burning velocity measurements were
utilized from the literature. Significant differences were found between
the performances of the various models investigated, and the performance
of a mechanism usually varies significantly with the type of experiment.
The results indicate that further mechanism development is needed to
reproduce the measurements more accurately under a wide range of
experimental conditions.
The performances of 18 recent detailed acetone combustion mechanisms were
quantitatively assessed against 16578 experimental data points of 228
experimental data series. The Mezaine-2022 reaction mechanism had the best
performance, but the three versions of AramcoMech, the Burke-2016 and the
Gong-2015 mechanisms also reproduced the experiments well. Local
sensitivity analysis showed that the most important reactions of acetone
combustion are the unimolecular decomposition of acetone molecule, CH3COCH3
= CH3CO + CH3 and its H abstraction reactions with
small radicals. Besides, some reactions of the methyl radical had
significant sensitivity.
The reaction kinetics (Re) branch of the ReSpecTh information system
(http://respecth.hu/) contains a large collection of indirect combustion
experimental data, like ignition delay times measured in shock tubes and
rapid compression machines, laminar burning velocities, and concentrations
determined in various types of reactors (151841 datapoints in 3239
datafiles). The data are related to the combustion of hydrogen, syngas,
methane, ammonia, methanol, ethanol, butanol, and NOx doped fuels. It also
contains directly measured or theoretically determined rate coefficients
of elementary reactions important in combustion systems (6884 data points
in 354 datafiles). The site contains numerous utility codes for the
validation, optimization, analysis, and reduction of detailed combustion
reaction mechanisms. The content of the ReSpecTh information system is
freely available after registration.
Among renewable combustible fuels, n-pentanol is considered as a potential
candidate. In this work, we proposed and applied a novel mechanism
reduction-assisted procedure to optimize rate parameters of the recently
developed n-pentanol part of the detailed NUIGMech 1.1 multifuel
combustion kinetic mechanism, which would be otherwise unfeasible.
According to our proposed method, first a precise reduced mechanism is
developed, which thus can be optimized effectively against experimental
targets, then the tuned parameter values are inserted back into the
detailed model, whose accuracy thereby can also be improved to a similar
extent.
In previous mechanism optimization studies, the active parameters were
selected based either on local sensitivity coefficients or on products of
the local sensitivity coefficient and the uncertainty of the parameters.
In this work, we propose a very efficient novel method, called PCALIN,
which uses not only the local sensitivities, but also considers the
uncertainty and the correlation of parameters, and furthermore the
uncertainty and the weights of the experimental data. The method also
identifies the relevant subset of the experimental data collection,
thereby allows significant savings in computation time at mechanism
optimization.
Comparison of the performance of
ethylene combustion mechanisms based on large number of indirect
measurements
Proceedings of the 15th
International Conference on Combustion Technologies for a Clean
Environment, June 25-29, 2023, Lisbon, Portugal
ABSTRACT
A large amount of experimental data covering wide ranges of conditions on
ethylene combustion has been collected from the literature: ignition delay
times measured in shock tubes (1160 data points in 114 data series) and
rapid compression machines (83/5), concentration measurements carried out
in jet-stirred reactors (1586/157) and flow reactors (649/59), and laminar
burning velocities (882/59). The standard deviations of these measurements
were estimated using both the published experimental uncertainty and the
scatter error of the data series. 14 detailed reaction mechanisms were
investigated using the collected experimental data. The results show
significant differences between the performances of the various
mechanisms. The four best-performing mechanisms are Aramco-2.0-2016,
Aramco-3.0-2018, NUIGMech-1.1-2020, and Yang-2020 (in this decreasing
order) based on all included experimental data. The best-performing model
Aramco-2.0-2016 was further investigated by local sensitivity analysis.
Several important reaction steps belonging to the hydrogen, syngas, and C1
systems were found to be important for all types of experiments, and
furthermore reactions C2H3 + O2 = CH2CHO
+ O and C2H4 + OH = C2H3 + H2O
which are specific for ethylene combustion.
Ignition delay time (IDT, τ) is the time period from the onset of a given temperature and pressure of a combustible gas mixture to the time of ignition. The time point of ignition is defined as reaching a given condition of pressure, temperature, or one of the species concentrations. In measurements, ignition of hydrocarbons and oxygenates is usually detected based on monitoring the change of pressure or the concentrations of species OH*, CH*, or CO2. In simulations, ignition is also detected based on the temperature profile. Simulated ignition of CH4/O2/N2 mixtures was investigated in a wide range of initial temperature (700-3000 K), pressure (0.05-500 atm), and equivalence ratio (φ=0.03-8.0) at two diluent-to-oxygen ratios: 3.76 (corresponding to air), 24.0 (corresponding to the conditions of many shock tube measurements). The agreement between τp and τOH* was good below initial temperature 2500 K and 0.5<φ<2.0, while the agreement between τp and values of τCH*, τCO2 and τT was much more than 10% for most of the conditions. The τOH vs. τOH* agreement is poor above φ=3.0 for most conditions. The τCH vs. τCH* agreement is good in the range of φ = 0.4 to 1.5, below 2200 K and 100 atm. The experimental determinations of IDTs should consistently be reproduced by simulations using exactly the same IDT definition. When different IDT definitions are used in various measurements or simulations, the τ values are expected to be in good agreement only in restricted ranges of conditions.
The present paper studies the energy intensity of ammonia production by a
freely oscillating microbubble placed in an infinite domain of liquid. The
initial content of the bubble is a mixture of hydrogen and nitrogen. The
bubble is expanded isothermically to a maximum radius, then it is
“released” and oscillates freely. The input energy is composed of the
potential energy of the bubble at the maximum radius, the energy required
to produce hydrogen, and the pumping work in case a vacuum is employed.
The chemical yield is computed by solving the underlying governing
equations: the Keller–
Miksis equation for the radial dynamics, the first law of thermodynamics
for the internal temperature and the reaction mechanism for the evolution
of the concentration of the chemical species. The control parameters
during the simulations are the equilibrium bubble size, initial expansion
ratio, ambient pressure, the initial concentration ratio of hydrogen and
the material properties of the liquid. At the optimal parameter setup, the
energy intensity is 90.17 GJ/t that is 2.31 times higher than the best
available technology, the Haber–Bosch process. In both cases, the hydrogen
is generated via water electrolysis.
The core chemistry and thermodynamic data of large alkanes in the NUIGMech mechanism were recently updated. In the present work, the set of rate rules for large alkanes is optimized against experimental data to improve the predictivity of the mechanism. As a starting step of developing a consistent set of rate rules for any larger alkane, we optimized the mechanism of pentane isomers, whose mechanism was generated based on 185 rate rules in 24 reaction classes using code MAMOX++. Including the core chemistry, the mechanism contained 1427 species and 6676 reactions. For the efficient optimization of such a large mechanism, the Optima++ code was extended to rate rules and was linked with the Zero-RK simulation code. As reference data, first-stage and total ignition delay times measured in shock tubes and rapid compression machines and species concentrations measured in jet-stirred reactors were collected in wide ranges of conditions. The prior uncertainties of the Arrhenius equations of the 185 rate rules were determined based on a review of alkanes’ rate constant studies. The PCA-SUE method was used for the selection of the influential rate rules. This method identified 94 important rate rules whose Arrhenius parameters were subsequently optimized within their prior uncertainty ranges using Optima++ against a representative data collection subset with a moderate computational effort. The optimization significantly improved the accuracy of the mechanism, which now performs significantly better even than the Bugler et al. mechanism (PROCI, 2017). The present study has demonstrated the effectiveness of the proposed methodology, thereby paving the way to the optimization of a complete set of rate rules that can be used for the generation of a reliable combustion mechanism for any larger alkane, and with some extensions even for unsaturated fuels or oxygenated fuels such as biodiesels.
Investigating the methanol (CH3OH) / nitrogen-oxides (NOx) combustion system is an important task since methanol is a promising alternative to fossil fuels, and its interactions with nitrogen oxides are significant due to environmental effects. The performances of the recently available detailed mechanisms in simulating the experimental results are still unsatisfactory. The aim of this work is to develop a more reliable reaction mechanism using parameter optimization. First, the Glarborg-2018 mechanism was updated with the rate parameters of the previously optimized H2/NOx and methanol mechanisms of ELTE. A large collection of literature data was compiled, which consists of direct measurements and theoretical determinations of the rate coefficients (2175 data points in 130 data series), indirect measurements of the formaldehyde (CH2O) /NOx and CH3OH/NOx system in homogenous reactors (2373 data points in 225 data series), and the neat CH3OH and CH2O subsystems in homogenous reactors and flames (689 data points in 68 data series). Using code Optima++, we optimized the rate parameters of the 24 most important elementary reactions that were identified by the recent PCALIN (Principal Component Analysis of the Parameter-Uncertainty and Data-Uncertainty Scaled Local Sensitivity Matrix with Linear Corrections) active parameter selection method as most influential. The optimized rate coefficients were assessed in detail and compared with literature data. The optimized mechanism can reproduce the CH2O/NOx and CH3OH/NOx combustion experimental data on average within their 3.5σ experimental uncertainty, which means it performs significantly better than the previously published mechanisms, which have average errors larger than 5σ. The reproduction of neat CH3OH and CH2O experimental data also improved. The optimized mechanism was also tested on experimental data of the H2, H2/NOx, syngas, and syngas/NOx combustion systems. In all cases, the optimized mechanism reproduced these experimental data better than the initial mechanism, although these data were not used as optimization targets.
The critical advantages of liquid fuels in aviation over alternative energy carriers imply their dominance in the upcoming decades. The Mixture Temperature Controlled (MTC) combustion concept allows spatially homogeneous, efficient burning (distributed combustion) with low pollutant emission. MTC combustion of jet fuel JP-8 was investigated in an atmospheric burner, and the measured pollutant concentrations in the flue gas were reproduced using the Hybrid Chemistry (HyChem) approach employing Perfectly Stirred Reactor simulations. Using this robust approach comes with losing spatiotemporal characteristics if the mixture homogeneity assumption is globally valid. The effect of residence time and pressure under typical gas turbine operating conditions was investigated. Stable combustion was present above 3 ms residence time at all pressures, while the lower limit was 0.3 ms. The residence time interval of stable operation could be extended by applying flue gas recirculation. NO emission can be reduced by increasing the operating pressure, while the N2O production is dominant only up to 20 bar and in the 10–100 ms residence time range. CO emission vanishes above 10 ms residence time. Ultra-low emission operation requires >20 bar pressure and 10 ms residence time with distributed combustion, requiring larger combustion chambers for future jet engines.
Testing detailed combustion mechanisms typically concludes that some mechanisms reproduce the experimental data well at most conditions but are inaccurate at other conditions. However, other mechanisms may perform well under these conditions. A better mechanism (“mosaic mechanism”) may be obtained by identifying the overall best-performing mechanism and loaning the most important reaction steps and their rate parameters from another mechanism with good performance at the conditions where the overall best model is ill-performing. A new algorithm based on this approach is presented here, which is successfully applied using a comprehensive collection of NH3/air laminar burning velocity data (348 data points in 61 data series) and eight recent detailed NH3 combustion mechanisms. The suggested new mosaic mechanism is an improved version of the CEU-2022 mechanism and provides a better reproduction of the utilised data than the previously published mechanisms. The proposed algorithm can be applied to any chemical kinetics system and any other types of experiments. All data needed to apply the algorithm to various combustion systems are already available or can be generated with minimal human effort using the experimental data files, mechanisms, and codes available on the ReSpecTh (https://ReSpecTh.hu) website.