Effect of dimethoxymethane addition on the experimental structure of a rich ethylene/oxygen/argon flame

Structures of premixed ethylene/oxygen/argon-rich flat flames burning at 50 mbar have been established by using molecular beam mass spectrometry to investigate the effect of methylal (dimethoxymethane) addition on species concentration profiles. The aim of this experimental study is to examine eventual changes of the concentration profiles of detected hydrocarbon intermediates which could be considered as soot precursors (C2H2, C4H2, C5H4, C5H6, C5H8, C6H2, C6H4, C6H6, C6H8, C7H8, C6H6O, C8H6, C8H8, C9H8, and C10H8). The comparative study has been achieved on three flames with equivalence ratios (phi) of 2.25 and 2.50: two without any additive (F2.25 and F2.50) and one with 4.3% methylal in partial replacement of C2H4 (F2.50M). The three flat flames have similar final flame temperatures (congruent to1800 K). An increase of the flame equivalence ratio (0) from 2.25 to 2.50 leads to an increase of maximum mote fractions of most hydrocarbon intermediates, much larger than the initial fuel content difference. Methylal addition to the fresh gas inlet causes a slight shift downstream of the flame front. 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 C-2 to C-4 intermediates, it becomes more efficient for C-5 to C-10 species. Although the equivalence ratio is quite different in flames F2.25 and F.2.50M, most of the maximum mole fractions Of C-2 to C-10 intermediates are very similar but lower than those in the F2.50 flame. It seems to indicate that similar initial C/O ratio (F2.25, 0.75; F2.50M, 0.76) in the fresh gases mixtures better encapsulates the influence on maximum concentrations of hydrocarbon intermediates and soot precursors in rich flames.