Measurement of soot volume fraction and gaseous species concentrations in premixed N-heptane and iso-octane flames

The main objective of this work was to correlate in n-heptane and iso-octane flames the soot volume fraction and the mole fraction of benzene and its precursors. Both series of measurements were performed in premixed laminar flames stabilised at atmospheric pressure on a flat flame burner. Soot volume fraction profiles were derived from attenuation of a 670 nm Helium-Neon laser beam. Species concentration profiles were obtained by gas Chromatography analysis of samples withdrawn with fine quartz microprobes. Species analysed (benzene, acetylene, allene, propyne, vinylacetylene) exhibit a maximum prior the onset of soot formation. Additional gas species measurements were performed in the sooting region. A wide range of equivalence ratio was investigated : from 1.5 to 2.24 for n-heptane and from 1.5 to 2.16 for isooctane flames. Results show that the soot volume fraction is strongly correlated to the local acetylene concentration. On the other hand, no correlation is observed with benzene since for a given equivalence ratio, the soot concentrations measured for each fuel are almost similar while benzene concentration is markedly higher in the isooctane flames.