Pre-Particle Chemistry in Soot Formation

Abstract

Species and reactions involved in the early stages of soot formation prior to the formation of particles have been studied in flat low pressure flames of benzene using a molecular beam mass spectrometer system. In a near-sooting (equivalence ratio φ = 1.8) benzene-oxygen-argon flame, the profiles of molar flux versus distance from the burner for several reactant, intermediate, and product species were calculated from the mole fraction profiles. The flux profiles indicate that CO, C6H6O and C5H6 are early intermediates in the ring destruction process but that C2H2 is not. The flux profiles of C6H6 and C2H2 are consistent with benzene consumption by OH addition and the OH + C6H6 reaction having a much larger rate coefficient than OH + C2H2. A mechanism is outlined for production of C1, C2, C3, C4 and C5 species from benzene that is consistent with the flux profiles of intermediate species. The production of more hydrogenated species from those of low H/C ratio as they diffuse toward the burner surface is discussed.