Total number of citations: 1433 (as of 1st March, 2010). Hirsch index = 21.
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
(Cited 4 times)
2 A.
Császár, P. Érdi, L. Jicsinszky, T.
Tóth, T. Turányi
Several exact results on
deterministic exotic kinetics
Z.phys.Chemie,
Leibzig, 264, 449-463(1983)
ABSTRACT
(Cited 3 times)
3 S. Vajda,
P. Valkó, T. Turányi
Principal component
analysis of kinetic models
Int.J.Chem.Kinet.,
17, 55-81(1985)
ABSTRACT
(Cited 130 times)
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
(Cited 22 times)
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
(Cited 0 times)
6 L.
Haszpra, T. Turányi
Production of nitric
acid in the atmosphere under different conditions
Időjárás,
90, 332-338(1986)
ABSTRACT
(Cited 0 times)
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
(Cited 0 times)
8 T.
Turányi, T. Bérces, J. Tóth
The method of
quasi-stationary sensitivity analysis
J.Math.Chem.,
2, 401-410(1988)
ABSTRACT
(Cited 0 times)
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
(Cited 0 times)
10 T. Turányi, T.
Bérces, S. Vajda
Reaction rate analysis
of complex kinetics systems
Int.J.Chem.Kinet.,
21, 83-99(1989)
ABSTRACT
(Cited 67 times)
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
(Cited 5 times)
12 T. Turányi
Rate sensitivity
analysis of a model of the Briggs-Rauscher reaction
React.Kinet.Catal.Lett.,
45, 235-241(1991)
ABSTRACT (Cited
17 times)
13 T. Turányi
KINAL: A program
package for kinetic analysis of complex reaction mechanisms
Comp.Chem.,
14, 253-254(1990)
ABSTRACT
(Cited 58 times)
14 T. Turányi
Reduction of large
reaction mechanisms
New J.Chem., 14, 795-803(1990)
ABSTRACT
(Cited 55 times)
15 T. Turányi
Sensitivity analysis of
complex kinetic systems: Tools and applications
J.Math.Chem.,
5, 203-248(1990)
ABSTRACT
(Cited 154 times)
16 L. Györgyi, T.
Turányi, R.J. Field
Mechanistic details of
the oscillatory Belousov-Zhabotinskii reaction
J.Phys.Chem.,
94, 7162-7170(1990)
ABSTRACT
(Cited 125 times)
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
(Cited 33 times)
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
(Cited 7 times)
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
(Cited 30 times)
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
(Cited 0 times)
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
(Cited 40 times)
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
(Cited 29 times)
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
(Cited 61 times)
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
(Cited 19 times)
25 T. Turányi
Computational
investigation of the kinetics of reaction systems (in Hungarian)
Kemiai
kozlemenyek, 75, 97-110(1992)
ABSTRACT
(Cited 0 times)
26 T. Bérces, T.
Turányi
Role of chemistry in the
characterization and depletion of air pollution (in Hungarian)
Kemiai
kozlemenyek, 75, 7-16(1992)
(Cited 0 times)
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
(Cited 6 times)
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
(Cited 1 times)
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
(Cited 0 times)
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
(Cited 1 times)
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
(Cited 0 times)
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)
(Cited 0 times)
33 T. Turányi
Parameterization
of reaction mechanisms using orthonormal polynomials
Computers
Chem., 18, 45-54(1994)
ABSTRACT
(Cited 50 times)
34 T. Turányi
Application of
repro-modelling for the reduction of combustion mechanisms
Proc.Combust.Inst.,
25, 949-955(1995)
ABSTRACT
(Cited 21 times)
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,
Elsevier, 1997, pp. 293-437
ABSTRACT
(Cited 158 times)
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
(Cited 8 times)
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
(Cited 0 times)
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
(Cited 53 times)
39 T. Turányi
Applications of
sensitivity analysis to combustion chemistry
Reliability
Engineering & System Safety, 57,
41-48(1997)
ABSTRACT
(Cited 21 times)
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
(Cited 1 times)
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
(Cited 6 times)
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 (Cited 25 times)
43 A. Obieglo, J. Gass, A. Buki,
T. Turányi
PDF-Berechnung einer
turbulenten Flamme unter Verwendung des Repromodellierens
VDI Berichte, 1492, 487-492(1999)
ABSTRACT
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 68 times)
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
(Cited 23 times)
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
(Cited 0 times)
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
(Cited 1 times)
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
(Cited 3 times)
50 I.Gy.
Zsély, T. Turányi
Investigation and reduction
of two methane combustion mechanisms
Archivum
Combustionis, 21, 173-177(2001)
ABSTRACT
(Cited 1 times)
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
(Cited 23 times)
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
(Cited 5 times)
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
(Cited 0 times)
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
(Cited 12 times)
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
(Cited 4 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 0 times)
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
(Cited 3 times)
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
(Cited 1 times)
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
(Cited 4 times)
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
(Cited 2 times)
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
(Cited 0 times)
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
(Cited 19 times)
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
(Cited 10 times)
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
(Cited 8 times)
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
(Cited 0 times)
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
(Cited 1 times)
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
(Cited 4 times)
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
(Cited 1 times)
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
(Cited 12 times)
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
(Cited 0 times)
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
(Cited 1 times)
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
(Cited 1 times)
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
(Cited 1 times)
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
(Cited 6 times)
82 R. Lovas, J. Patvarczki, P.
Kacsuk, I. Lagzi,
T. Turányi, L. Kullmann, L. Haszpra, R. Mészaros,
A. Horanyi, 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.):
in.
Parallel Computing: Current
& Future Issues of High-End Computing, pp. 121-128,
John von
Neumann Institute for Computing Series Vol. 33,
Julich,
Germany 2005, ISBN 3-00-017352-8
ABSTRACT
(Cited 1 times)
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
(Cited 1 times)
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
(Cited 5 times)
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.
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.