COMPARISONS OF THE SOOT VOLUME FRACTION USING GRAVIMETRIC AND LIGHT EXTINCTION TECHNIQUES

Simultaneous optical and gravimetric measurements were performed in the postflame region of an acetylene/ air premixed flame where the temperature of the soot/gas mixture was reduced to 500 K through nitrogen dilution. By combining gravimetric measurements of the collected soot with soot density measurements using helium pycnometry, an accurate value of the soot volume fraction was obtained. The temperature and soot concentration profiles were measured to compare the line of sight light extinction measurement with the point sampling gravimetric measurements. The soot volume fraction obtained by light extinction measurements overestimated the actual soot volume fraction by about a factor of two. By calibrating the optical measurements with the gravimetric soot volume fractions, a dimensionless extinction coefficient, K-e, of 8.6 was measured. This value is conjectured to be applicable for soot generated for a variety of fuels and to be valid for extinction wavelengths in the visible to the near-infrared. It was also found that the mass specific light extinction coefficient was found to be 8.0 m(2)/g which is consistent with measurements reported in the literature for a variety of fuels.