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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

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

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

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN

Cool flame Autoignition

Slow reaction

Pressure-temperature diagram in the case of 1,3-dioxan

H2C CH2 CH2 H2C

Static reactor

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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)

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

PHENOMENA OBSERVED DURING THE REACTION BETWEEN HYDROCARBON AND OXYGEN

Cool flame Autoignition

Slow reaction

Pressure-temperature diagram in the case of 1,3-dioxan

H2C CH2 CH2 H2C

Static reactor

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

AUTOIGNITION

Starts like a cool flame, but does not stop Rise of temperature

  • ver 500°C
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SLIDE 6

5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Prevention of explosions during

  • xidation processes

Prediction of the phenomena

  • bserved during the
  • xidation of hydrocarbons

Development of detailed chemical mechanisms for the oxidation and autoignition

  • f hydrocarbons

by using an automatic generator

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

AUTOMATIC GENERATOR OF DETAILED MECHANISMS OF COMBUSTION

Primary Mechanism Generator

Reaction Model in a CHEMKIN II Format

Lumped Primary Molecules Free Radicals

Reactants

EXGAS

Kinetic Data Thermochemical Data

KINGAS

Thermochemical Data

Reaction Bases

C2-Molecules and Free Radicals

THERGAS Primary Mechanism Generator Reaction Bases Secondary Mechanism Generator Secondary Mechanism Generator THERGAS KINGAS

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

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
  • xidation 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

GENERIC ELEMENTARY REACTIONS IN THE PRIMARY MECHANISM OF AKKANES

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

STRUCTURE OF THE PRIMARY MECHANISM FOR ALKANES

Initial reactant

hydroperoxyalkene + •OOH

  • xo - hydroperoxyalkane + •OH

hydroperoxy-cycloether + •OH di-hydroperoxyalkane + •R' di-hydroperoxyalkene + •OOH bs

O2 O2

adox

  • OOR
  • QOOH
  • OOQOOH
  • U(OOH)2

hydroperoxyalkane + •R' hydroperoxyalkene + O2 cyclic ether + •OH hydroperoxyalkane + •R' hydroperoxyalkene + •OOH

di-hydroperoxyalkane + •R' me dis

  • x

me

  • r

bs me

  • r

bs me

conjugated olefin + •OOH aldehyde / ketone + •OH hydroperoxyalkene + •R' hydroperoxyalkene + •R'

  • x

is is is is is is

O2 O2

adox bs

+ HO2 ui bi

  • R'

me

conjugated olefin + •OOH

  • R

+ O2

  • lefin + •R'

bs

  • x

is

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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 (per H atom) Primary H (i.e. R-CH3) Secondary H (i.e. R1-CH2-R2) lg A b E lg A b E Initiation with O2 112.6 205 12.00 201 Oxidation 11.37 20.9 11.90 20.9 H-atom abstraction by

  • O•

13.23 32.8 13.11 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 39.8

  • OOH

11.30 71.1 11.30 64.8 Other reactions lg A b E Addition of a free radical on O2 19.34

  • 2.5

Beta-scission

to •CH3 + molecule

13.30 130.0

  • f a free

to •R + molecule

13.30 120.0 radical

to •OOH + molecule

12.92 108.7

to •OH + molecule

9.00 31.3 Cyclic 3 members ring 12.00 69.0 ether 4 members ring 11.30 64.8 formation 5 members ring 10.77 37.6 6 members ring 10.00 25.1 Disproportionation of •OOR and

  • OOH

11.30

  • 5.43

Isomerizations and unimolecular initiations Calculated according to the methods proposed by S.W. Benson

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Examples of predictions using detailed kinetic mechanisms generated by EXGAS

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

0.0 0.5 1.0 1.5 2.0 2.5 550 600 650 700 750 800 2-stage ignition

T / K % n-C4H10 by volume in air

slow reaction cool flame slow reaction single stage ignition

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)

Simulations

Black lines : Simulations performed in Leeds with a mechanism generated in Nancy

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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

1.0 1.5 2.0 2.5 600 800 1000 1200 1400 1600

T / K t / s

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions Rapid compression machine of Lille (R. Minetti and M. Ribaucour)

N-heptane Modeling of the reaction in a rapid compression machine

Tafter compression = 706 K, Pafter compression = 3.2 bar, Φ = 1

1.2x10

6

1 0.8 0.6 0.4 Pressure (bar) 40x10

  • 3

30 20 10 Residence time (s) 200x10

  • 6

150 100 50 Mole fraction Ignition delay time Pressure OH mole fraction H2O2 mole fraction /2500

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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

0.1 1 10 100 1000 Ignition delays times (ms) 1.4 1.2 1.0 0.8 1000/T (K) 3.2 bar : (RCM) (ST) 13.5 bar : (ST), 42 bar : (ST)

1000K 800K 700K

Negative temperature coefficient (NTC) region

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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

0.1 1 10 100 Ignition delay times (ms) 1.4 1.2 1.0 0.8 1000/T (K)

12 bar 50 bar

1000K 800K 700K NTC region displaced towards the higher temperatures when the pressure increases

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5th International Symposium on Hazard Prevention and Mitigation of Industrial Explosions

Detailed chemical mechanisms for the oxidation and autoignition

  • f alkanes

automatically generated

Semi quantitative prediction of the experimental conditions

  • f the different oxidation phenomena (cool flame, ignition)

Quantitative modeling of autoignition delay times in given conditions Prediction of the formation of intermediate products