Cédric Renard

Modeling of Rich Premixed C2H4/O-2/Ar and C2H4/Dimethoxymethane/O-2/Ar Flames

Abstract Two rich premixed ethylene/oxygen/argon and ethylene/dimethoxymethane/oxygen/argon flat flames burning at 50 mbar were investigated experimentally by using molecular beam mass spectrometry to study the effect of methylal (dimethoxymethane) addition on species concentration profiles (C. Renard, P.J. Van Tiggelen and J. Vandooren, Proc. Combust. Inst., 29 (2002) 1277–1284). The replacement of 5.7% C2H4 by 4.3% C3H8O2, keeping the equivalence ratio equal to 2.50, is responsible for a decrease of the maximum mole fractions of most of the detected intermediate species. If this phenomenon is barely noticeable for C2 to C4 intermediates, it becomes more efficient for C5 to C10 species. Previously, a reaction mechanism has been validated against a premixed rich C2H4/O2/Ar flame (φ = 2.50) which describes in detail the formation of soot precursors and more precisely the main pathways involving benzene (V. Dias, C. Renard, P.J. Van Tiggelen and J. Vandooren, European Combustion Meeting, Orléans, France, p.221, 2003).The aim of this work is to extend this original model by building a sub-mechanism taking into account the formation and the consumption of oxygenated species involved in dimethoxymethane combustion. The new mechanism contains 474 elementary reactions and involves 90 chemical species in order to simulate both ethylene flames with and without methylal addition. The model leads to a good simulation for all species detected in these flames, and underlines the effect of methylal addition on species concentration profiles.According to this mechanism, the two main degradation pathways of methylal (CH3OCH2OCH3) in C2H4/methylal/oxygen/argon flame are: 1) CH3OCH2javascript:filterformular(´3´)OCH3 → CH3OCH2OCH2 → CH3OCH2 → CH2O 2) CH3OCH2OCH3 → CH3OCHOCH3 → CH3OCHO → CH3OCO → CH3O → CH3OH → CH2OH → CH2O with the first one being the fastest.

MASS SPECTROMETRY, GAS CHROMATOGRAPHY, AND COUPLING GC/MS AS COMPLEMENTARY TECHNIQUES FOR FLAME STRUCTURE ANALYSIS

Molecular beam mass spectrometry (MBMS) and gas chromatography (GC) are complementary methods that provide a detailed description of flame structures. MBMS can measure most stable and reactive species but mass overlapping (isomers, species at same m/e), isotopic, and ionic fragmentation interferences can be solved by using GC. To improve species identification, an experimental technique coupling both mass spectrometry and GC is developed. Rich flat premixed ethylene/oxygen/argon flames (φ = 2.25 and 2.50) have been investigated by both methods. After adequate calibrations, mole fraction profiles of several species measured by both techniques agree very well, but for methane, allene, propyne, and benzene, concentrations in burnt gases are somewhat larger when using GC than when using MBMS. C2H6, C2H4O, C3H6, and C3H8, which have similar masses as CH2O, CO2 or C3H8, CH2CO, and CO2, respectively, have been identified, separated, and calibrated by GC, which confirms that GC and MBMS are complementary techniques.