MEASUREMENT OF SOOT VOLUME FRACTION AND GASEOUS SPECIES CONCENTRATIONS IN PREMIXED N-HEPTANE AND ISOOCTANE 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 benzen e and its precursors. Both series of measurements were performed in pr emixed laminar flames stabilised at atmospheric pressure on a flat fla me burner. Soot volume fraction profiles were derived from attenuation of a 670 nm Helium-Neon laser beam. Species concentration profiles we re obtained by gas Chromatography analysis of samples withdrawn with f ine quartz microprobes. Species analysed (benzene, acetylene, allene, propyne, vinylacetylene) exhibit a maximum prior the onset oi. soot fo rmation. Additional gas species measurements were performed in the soo ting 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 t he local acetylene concentration. On the other hand, no correlation is observed with benzene since for a given equivalence ratio, the soot c oncentrations measured for each fuel are almost similar while benzene concentration is markedly higher in the isooctane flames.