| OCR Text |
Show 5 Simulation In order to predict the diameter change and the existence ratio of four kinds shape of soot by benzene pyrolysis, we develop the model of benzene pyrolysis reaction based on the work of Ivie et al. [1]. This model includes four kinds of reactions, which are pyrolysis, nucleation, surface growth and coagulation described below. 1. Pyrolysis of benzene The first step of the soot formation is the generation of soot precursors. It is assumed that a phenyl and a biphenyl radical are the precursors, because both chemical species are derived from benzene as ; CQHQ -• C6H54H2, (3) C6H6 + H -> C6H5+H2 , (4) C 6 H 6 4 C 6 H 5 -» C1 2H1 04H, (5) C12H10 - 2C6H5. (6) 2. Nucleation After the precursors are formed, the growth molecules begin colliding. C2H2, C2H3 and C4H3 called growth species are generated by pyrolysis of C6H5. The nuclei of carbon particles is assumed to be formed when a phenyl radical or a biphenyl radical grows to molecule which contains 14 carbon atoms. Because of the availability of phenyl radicals and biphenyl molecules during the benzene pyrolysis, these species are assumed to grow to the initial nuclei. The nucleation reaction is expressed as follows : Ny+nGx^>Pa, (7) Nr nucleating species containing y carbons (C6H5 and C12H]0), G^ growth species containing x carbons (C2H2, C2H3 and C4H3), Pa: particle containing 14 carbons, n- {'\A-y)x. For example, a phenyl radical collides with four acetylenes before the particle containing 14 carbon atoms (a nucleus) is formed. A nucleus is also formed when a biphenyl molecule collides with C2H3 or C2H2; otherwise a phenyl radical collides with two diacetylenes (C4H3). 3. Surface Growth |
