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Chemkin 4.1.1 Chapter 2: Combustion in Gas-phase Processes The A-factor computed from the collision frequency between A4 molecules is of the order of 10 12 and is much larger than the one used in the above nucleation reaction. 2.8.5.2 Soot Mass Growth Reactions One of the advantages of the Particle Tracking Module is that soot mass growth and oxidation reactions can be provided as regular surface reactions. For example, the H- Abstraction-C 2 H 2 -Addition (HACA) soot growth sequence proposed by Frenklach and coworkers 25,26 can be given as: (S2) H+H(S)=>(S)+H2 4.20E13 0.0 13000.0 (S3) H2+(S)=>H(S)+H 3.90E12 0.0 9320.0 (S4) H+(S)=>H(S) 2.00E13 0.0 0.0 (S5) H(S)+OH=>H2O+(S) 1.00E10 0.734 1430.0 (S6) H2O+(S)=>OH+H(S) 3.68E08 1.139 17100.0 (S7) C2H2+(S)=>H(S)+2C(B)+H 8.00E07 1.56 3800.0 It is easy to see that each sweep of the HACA growth sequence will increase the soot particles by two classes. Marr 23 (see p. 78) suggested that PAH condensation on the soot particle surface can have significant contribution to soot mass growth in post flame zone. He also found from his experimental study that the collision efficiency of PAH condensation is of the order of 0.1. Since a description on how PAH species interact with a soot particle is not readily available, the PAH condensation reactions used in the simulation are purely hypothetical. Only condensations of major PAH species in the gas mechanism are considered. The reaction orders are determined by fitting the experimental data while keeping the sticking coefficients within the order of 0.1. Basically, the PAH condensation reactions used here are designed to increase soot particle mass in two ways: they grow the soot particle by the addition of PAH species and they remove some H atoms (H(S)) on the soot particle surface so that the more effective soot growth reaction, C 2 H 2 addition (S7), can proceed at a greater rate. © 2007 Reaction Design 88 RD0411-C20-000-001
Chapter 2: Combustion in Gas-phase Processes <strong>Tutorials</strong> <strong>Manual</strong> (S8) A1+6H(S)=>6C(B)+6(S)+6H2 0.2 0.0 0.0 FORD/H(S) 1.0/ FORD/(S) 1.0/ DCOL/2.46E-8/ STICK (S9) A1C2H+6H(S)=>8C(B)+6(S)+6H2 0.21 0.0 0.0 FORD/H(S) 2.0/ DCOL/2.46E-8/ STICK (S10) A2+16H(S)=>10C(B)+16(S)+12H2 0.1 0.0 0.0 FORD/H(S) 2.0/ DCOL/4.92E-8/ STICK (S11) A2R5+16H(S)=>10C(B)+16(S)+11H2+C2H20.1 0.0 0.0 FORD/H(S) 2.0/ DCOL/4.92E-8/ STICK (S12) A3+20H(S)=>14C(B)+20(S)+15H2 0.1 0.0 0.0 FORD/H(S) 2.0/ DCOL/4.92E-8/ STICK (S13) A4+20H(S)=>16C(B)+20(S)+15H2 0.1 0.0 0.0 FORD/H(S) 2.0/ DCOL/4.92E-8/ STICK Expressing the soot growth sequence as a chain of surface reactions has other advantages. As part of surface mechanism, it is easy to check for the conservation of elements and to perform sensitivity analysis and optimization to these reactions. If information about certain reactions, such as PAH condensation, is available from surface-science experiments, utilization of such information would be straightforward. RD0411-C20-000-001 89 © 2007 Reaction Design
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August 3, 2007 1:53 am Release 4.1.
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Chemkin 4.1.1 Contents Table of Con
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Chemkin 4.1.1 Tables List of Tables
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Tutorials Manual 4.1.1 Figures List
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List of Figures Tutorials Manual 2-
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Chemkin 4.1.1 1 1 Introduction The
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Chapter 1: Introduction Tutorials M
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Chemkin 4.1.1 2 2 Combustion in Gas
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Chapter 2: Combustion in Gas-phase
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Tutorials Manual 4.1.1 Index Index
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