Experimental and Modeling Studies of Benzene Formation in Rich Premixed Ethylene Flames V. Dias, C. Renard, P. J. Van Tiggelen and J. Vandooren dias@chim.ucl.ac.be CSTR – Laboratoire de Physico-Chimie de la Combustion Université catholique de Louvain – Place Louis Pasteur, 1 1348 Louvain-la-Neuve – Belgium Introduction Polycyclic Aromatic Hydrocarbons (PAH) are formed in most practical combustion systems and are important precursors of soot. It is now widely accepted that benzene and phenyl formations constitute the first step in this growth process that lead to PAH and ultimately soot particles. However, despite the extensive work on the elementary reactions leading to the first aromatic ring, the dominant benzene formation pathway does not seem to be identified. Two different sets of reactions had been proposed according the authors [1-11]: the C 4 hydrocarbons pathways with the reaction of n-C 4 H 5 and n-C 4 H 3 with C 2 H 2 ; and the C 3 hydrocarbons channel with the recombinaison of propargyl radical (C 3 H 3 ) and the reaction of C 3 H 3 with propyne (p-C 3 H 4 ). The aim of this work is to measure and to simulate the structure of rich premixed flames of ethylene-oxygen-argon. Since ethylene is an important intermediate during the hydrocarbon combustion, analysis of these flames allows us to determine mole fraction profiles of many chemical compounds, and to establish a kinetic mechanism of the formation of species from C 1 /C 2 to polycyclic aromatic hydrocarbons (soot precursors). Experimental One dimensional ethylene-oxygen-argon flames at equivalence ratios of 2.25 and 2.50 were stabilised at low pressure (50 mbar) on a Spalding-Botha-type burner. Gases sampling are performed by a quartz cone, at different heights in the flame. Identification and measurement of chemical species were performed by molecular beam mass spectrometry (MBMS) and by gas chromatography (GC). Moreover, two couplings of both techniques (GC/MS) were used to facilitate the identification of detected species [12]. The following species have been identified by both methods: CO, Ar, H 2 , O 2 , CH 4 , CO 2 , C 2 H 4 , C 2 H 2 , C 2 H 6 , H 2 O, C 3 H 6 , C 3 H 8 , C 3 H 4 (CH 2 CCH 2 and CHCCH 3 ), C 2 H 4 O, C 4 H 4 , C 4 H 6 , C 4 H 2 , C 4 H 8 , C 5 H 6 and C 6 H 6 . By MBMS only, compounds in lower concentration have been measured: C 6 H 2 , C 6 H 4 , C 6 H 6 O, C 7 H 8 , C 8 H 6 , C 8 H 8 , C 9 H 8 and C 10 H 8 . The sensitivity of the gas chromatograph does not allow to detect these last species with a Poraplot Q column; a different column should be used to analyse higher hydrocarbons than C 6 compounds. Modeling By comparison of kinetic models from the literature with the experimental results of rich ethylene-oxygen-argon flames (φ = 2.25 and 2.50) we were able to build a new mechanism of 400 reactions involving 77 species. Indeed, the numerical simulation for the formation and the consumption of C 2 to C 10 (naphthalene) species in all these flames is satisfactory.