Use of detailed kinetic mechanism for the prediction of - PowerPoint PPT Presentation

Use of detailed kinetic mechanism for the prediction of autoignitions F. Buda, P.A. Glaude, F. Battin-Leclerc DCPR-CNRS, Nancy, France R. Porter, K.J. Hughes and J.F. Griffiths School of Chemistry, University of Leeds, UK 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN Pressure-temperature diagram in the case of 1,3-dioxan 0 H 2 C CH 2 H 2 C CH 2 0 Cool flame Autoignition Slow reaction Static reactor 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

COOL FLAMES SINGLE DOUBLE Measurement of pressure by a pressure transducer Measurement of temperature by a small thermocouple Rise below 100 °C Formation of intermediate products (hydroperoxides) 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN Pressure-temperature diagram in the case of 1,3-dioxan 0 H 2 C CH 2 H 2 C CH 2 0 Cool flame Autoignition Slow reaction Static reactor 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

AUTOIGNITION Starts like a cool flame, but does not stop Rise of temperature over 500°C 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Prevention of explosions during oxidation processes Prediction of the phenomena observed during the oxidation of hydrocarbons Development of detailed chemical mechanisms for the oxidation and autoignition of hydrocarbons by using an automatic generator 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

AUTOMATIC GENERATOR OF DETAILED MECHANISMS OF COMBUSTION EXGAS Reaction Reaction Bases Bases Free Radicals Reaction Model Primary Primary C 2 -Molecules in a Reactants Mechanism Mechanism and CHEMKIN II Generator Generator Free Radicals Lumped Format Primary Molecules Secondary Secondary Mechanism Mechanism Generator Generator Thermochemical Data Kinetic Data KINGAS KINGAS THERGAS THERGAS Thermochemical Data 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

GENERIC ELEMENTARY REACTIONS IN THE PRIMARY MECHANISM OF AKKANES 1- Initiation reactions � unimolecular initiations (ui) : ch3/ch2/ch2/ch3 2 • ch2/ch3 � bimolecular initiations (bi) : ch3/ch2/ch2/ch3 + //(o)2 • o/oh + • ch(/ch3)/ch2/ch3 2- Propagation reactions � addition of free radicals on oxygen (adox) : • ch(/ch3)/ch2/ch3 + //(o)2 • o/o/ch(/ch3)/ch2/ch3 � isomerization of free radicals (is) : • o/o/ch(/ch3)/ch2/ch3 • ch2/ch(/o/oh)/ch2/ch3 � decomposition of free radicals by beta-scission (bs) : • ch(/ch3)/ch2/ch3 • ch3 + ch3/ch//ch2 � decomposition of free radicals to cycloethers (or) : • ch2/ch(/o/oh/)ch2/ch3 c(#1)h(/ch2/ch3)/ch2/o/1 + • oh � oxidation of free radicals (ox) : • ch(/ch3)/ch2/ch3 + //(o)2 ch3/ch2/ch//ch2 + • o/oh � metathesis reactions (me) : ch3/ch2/ch2/ch3 + • oh oh2 + • ch2/ch2/ch2/ch3 3- Termination reactions � combination of free radicals (co) : • ch2/oh + • ch(/ch3)2 ch(/ch3)2/ch2/oh � disproportionation of free radicals (dis) : • o/o/ch(/ch3)2 + • o/oh ch3/ch(/o/oh)/ch3 + //(o)2 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

STRUCTURE OF THE PRIMARY MECHANISM FOR ALKANES Initial reactant • R' ui bi me + O 2 olefin + •R' bs • R ox conjugated olefin + •OOH is O 2 O 2 adox bs dis •OOR hydroperoxyalkane + •R' me hydroperoxyalkene + O 2 + HO 2 is cyclic ether + •OH conjugated olefin + •OOH or hydroperoxyalkane + •R' •QOOH aldehyde / ketone + •OH bs me ox is hydroperoxyalkene + •OOH hydroperoxyalkene + •R' O 2 O 2 bs adox •OOQOOH di-hydroperoxyalkane + •R' me is hydroperoxyalkene + •OOH is is hydroperoxy-cycloether + •OH or di-hydroperoxyalkane + •R' •U(OOH)2 me bs oxo - hydroperoxyalkane + •OH ox is di-hydroperoxyalkene + •OOH hydroperoxyalkene + •R' 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

KINETIC DATA OF THE PRIMARY MECHANISM OF LINEAR ALKANES AT HIGH TEMPERATURE Combust. Flame, 114:81 (1998) Ph. D. Thesis of P.A. Glaude (1999) (k=AxTb x exp(-E/RT), Units : cm3, mol, s, kJ) H-abstraction Primary H Secondary H (per H atom) (i.e. R-CH 3 ) (i.e. R1-CH 2 -R2) lg A b E lg A b E Initiation with O2 112.6 0 205 12.00 0 201 Oxidation 11.37 0 20.9 11.90 0 20.9 H-atom abstraction by •O• 13.23 0 32.8 13.11 0 21.7 •H 6.98 2 32.2 6.65 2 20.9 •OH 5.95 2 1.88 6.11 2 -3.20 •CH3 -1 4 34.3 11.0 0 39.8 •OOH 11.30 0 71.1 11.30 0 64.8 Other reactions lg A b E Addition of a free radical on O2 19.34 -2.5 0 to •CH3 + molecule 13.30 0 130.0 Beta-scission of a free to •R + molecule 13.30 0 120.0 radical 12.92 0 108.7 to •OOH + molecule to •OH + molecule 9.00 0 31.3 Cyclic 3 members ring 12.00 0 69.0 ether 4 members ring 11.30 0 64.8 formation 5 members ring 10.77 0 37.6 6 members ring 10.00 0 25.1 Disproportionation of •OOR and 11.30 0 -5.43 •OOH Isomerizations and unimolecular Calculated according to the methods initiations proposed by S.W. Benson 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Examples of predictions using detailed kinetic mechanisms generated by EXGAS 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

N-butane Prediction of a composition – temperature ignition diagram mixture in air, at 0.2 MPa in a closed vessel 0.5 dm3 Color lines : Experiments ( M.R. Chandraratna and J.F. Griffiths, 1994, Combust. Flame ) Black lines : Simulations performed in Leeds with a mechanism generated in Nancy 800 Simulations 750 single stage ignition 700 slow reaction T / K 650 cool flame 2-stage ignition 600 550 slow reaction 0.0 0.5 1.0 1.5 2.0 2.5 % n-C 4 H 10 by volume in air 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

N-butane Simulated two-stage ignition profile 1.45 % in air, at 0.2 MPa and 600 K 1600 1400 1200 T / K 1000 800 600 1.0 1.5 2.0 2.5 t / s 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

N-heptane Modeling of the reaction in a rapid compression machine T after compression = 706 K, P after compression = 3.2 bar, Φ = 1 -6 200x10 6 1.2x10 Pressure OH mole fraction H 2 O 2 mole fraction /2500 150 1 Pressure (bar) Mole fraction Ignition delay time 0.8 100 0.6 50 Rapid compression machine of Lille 0.4 (R. Minetti and M. Ribaucour) 0 -3 0 10 20 30 40x10 Residence time (s) 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

N-heptane Modeling the autoignition delay times in a shock tube (ST) and in a rapid compression machine (RCM) ST : Ciezki H.K. and Adomeit G., 1993, Combust. Flame RCM : Minetti R., Carlier M., Ribaucour M., Therssen E. and L.R. Sochet, 1995, Combust. Flame Points are experiments, lines simulations, Φ = 1 1000K 800K 700K 1000 3.2 bar : (RCM) (ST) 13.5 bar : (ST), 42 bar : (ST) Ignition delays times (ms) 100 10 1 0.1 0.8 1.0 1.2 1.4 1000/T (K) Negative temperature coefficient (NTC) region 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

N-decane Modeling the autoignition in a shock tube Pfahl U., Fieweger K. and Adomeit, G., IDEA-EFFECT, Final Report, 1996 Points are experiments, lines simulations, Φ = 1 1000K 800K 700K 100 12 bar Ignition delay times (ms) 50 bar NTC region displaced 10 towards the higher temperatures when the pressure increases 1 0.1 0.8 1.0 1.2 1.4 1000/T (K) 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Detailed chemical mechanisms for the oxidation and autoignition of alkanes automatically generated � Semi quantitative prediction of the experimental conditions of the different oxidation phenomena (cool flame, ignition) � Quantitative modeling of autoignition delay times in given conditions � Prediction of the formation of intermediate products 5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions