Use of detailed kinetic mechanism for the prediction of autoignitions

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1 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

2 PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN Pressure-temperature diagram in the case of 1,3-dioxan H 2 C 0 CH 2 H 2 C 0 CH 2 Cool flame Static reactor Slow reaction Autoignition

3 COOL FLAMES SINGLE Measurement of pressure by a pressure transducer DOUBLE Measurement of temperature by a small thermocouple Rise below 100 C Formation of intermediate products (hydroperoxides)

4 PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN Pressure-temperature diagram in the case of 1,3-dioxan H 2 C 0 CH 2 H 2 C 0 CH 2 Cool flame Static reactor Slow reaction Autoignition

5 AUTOIGNITION Starts like a cool flame, but does not stop Rise of temperature over 500 C

6 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

7 AUTOMATIC GENERATOR OF DETAILED MECHANISMS OF COMBUSTION Reactants Thermochemical Data Free Radicals EXGAS Reaction Bases Primary C 2 -Molecules Mechanism and Generator Free Radicals Lumped Primary Molecules Secondary Mechanism Generator Kinetic Data Reaction Model in a CHEMKIN II Format THERGAS KINGAS Thermochemical Data

8 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

9 STRUCTURE OF THE PRIMARY MECHANISM FOR ALKANES hydroperoxy-cycloether + OH di-hydroperoxyalkane + R' di-hydroperoxyalkene + OOH O 2 Initial reactant bs adox hydroperoxyalkane + R' me OOR dis hydroperoxyalkene + O 2 is + HO 2 cyclic ether + OH hydroperoxyalkane + R' hydroperoxyalkene + OOH di-hydroperoxyalkane + R' R' me or me ox me or ox me O 2 is bs ui R is QOOH is OOQOOH is U(OOH)2 is bi + O 2 bs olefin + R' hydroperoxyalkene + OOH oxo - hydroperoxyalkane + OH is O 2 O 2 adox bs ox bs conjugated olefin + OOH conjugated olefin + OOH aldehyde / ketone + OH hydroperoxyalkene + R' hydroperoxyalkene + R'

10 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=axt b 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 O Oxidation H-atom abstraction by O H OH CH OOH Other reactions lg A b E Addition of a free radical on O to CH3 + molecule Beta-scission of a free to R + molecule radical to OOH + molecule to OH + molecule Cyclic 3 members ring ether 4 members ring formation 5 members ring members ring Disproportionation of OOR and OOH Isomerizations and unimolecular initiations Calculated according to the methods proposed by S.W. Benson

11 Examples of predictions using detailed kinetic mechanisms generated by EXGAS

12 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 cool flame 2-stage ignition 550 slow reaction % n-c 4 H 10 by volume in air

13 N-butane Simulated two-stage ignition profile 1.45 % in air, at 0.2 MPa and 600 K T / K t / s

$2x10 6 1 Pressure OH mole fraction H 2 O 2 mole fraction /2500 200x10-6 150 Rapid compression machine of Lille (R. Minetti and M. Ribaucour) Pressure (bar) 0.8 0.6 0.$

14 N-heptane Modeling of the reaction in a rapid compression machine T after compression = 706 K, P after compression = 3.2 bar, Φ = 1 1.2x Pressure OH mole fraction H 2 O 2 mole fraction / x Rapid compression machine of Lille (R. Minetti and M. Ribaucour) Pressure (bar) Ignition delay time Mole fraction Residence time (s) 0 40x10-3

15 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 = K 800K 700K Ignition delays times (ms) bar : (RCM) (ST) 13.5 bar : (ST), 42 bar : (ST) /T (K) 1.4 Negative temperature coefficient (NTC) region

16 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 = K 800K 700K Ignition delay times (ms) bar 50 bar NTC region displaced towards the higher temperatures when the pressure increases /T (K) 1.4

17 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

USE OF DETAILED KINETIC MECHANISMS FOR THE PREDICTION OF AUTOIGNITIONS

USE OF DETAILED KINETIC MECHANISMS FOR THE PREDICTION OF AUTOIGNITIONS F. Buda 1, P.A. Glaude 1, F. Battin-Leclerc 1*, R. Porter 2, K.J. Hughes 2 and J.F. Griffiths 2 1 DCPR-CNRS, 1, rue Grandville, BP