Etude de la formation des précurseurs des suies dans les flammes riches prémélangées d'éthylène
(2003)
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- Abstract
- Polycyclic Aromatic Hydrocarbons (PAHs) are formed in most rich premixed hydrocarbon flames. Many PAHs are carcinogenic and play an important role in the process of soot formation. Thus, it is essential to understand the pathways by which they are formed in order to inhibit their production and therefore to reduce the pollution. The aim of this work is to measure 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 C1 /C2 to polycyclic aromatic hydrocarbons (soot precursors). 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). Gas chromatography was used to supplement the results obtained by MBMS which detection limits are reached for heavy hydrocarbons having many isomers and subject to fragmentation and isotopic contributions. Moreover, a coupling of both techniques (GC/MS) were used to facilitate the identification of detected species. By comparison of kinetic models from the literature with the experimental results of rich ethylene-oxygen-argon flames (phi = 2.25 and 2.50) we were able to build a new mechanism of 400 reactions and involving 77 species. Its validity has been extended to ethylene flames at lower equivalence ratios: 1.00, 1.25, 1.50 and 1.75, to ethylene flames added with H2O or CO2 (phi = 2.50), as well as to methane, acetylene and ethane flames (phi = 1.00 to 2.00). Indeed, the numerical simulation for the formation and the consumption of C2 to C10 (naphthalene) species in all these flames is satisfactory. According to the nature of the initial fuel, the formation process of intermediate hydrocarbons is variable. This is successfully predicted by the mechanism, modeling the major production of the first aromatic ring via a C3 + C3 reaction in CH4, C2H4 and C2H6 flames, and via a C4 + C2 in C2H2 flames. Moreover, two major species are highlighted in the formation of heavier compounds: cyclopentadiene (C5H6) and benzene (C6H6). The latter is responsible for the production of phenol (C6H6O), toluene (C7H8), phenylacetylene (C8H6) and styrene (C8H8); besides taking part in the formation of indene (C9H8) and naphthalene (C10H8) in conjunction with cyclopentadiene.
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Citations
Dias, V. (2003). Etude de la formation des précurseurs des suies dans les flammes riches prémélangées d’éthylène. https://hdl.handle.net/2078.5/171922