FUEL PREHEAT EFFECTS ON SOOT-FIELD STRUCTURE IN LAMINAR GAS-JET DIFFUSION FLAMES BURNING IN 0-G AND 1-G

An experimental investigation conducted at the 2.2-s drop tower of the NASA Lewis Research Center is presented to quantify the influence of moderate fuel preheat on soot-field structure within 0-g laminar gas j et diffusion flames. Parallel work in 1-g is also presented to delinea te the effect of elevated fuel temperatures on soot-field structure in buoyant flames. The experimental methodology implements jet diffusion flames of nitrogen-diluted acetylene fuel burning in quiescent air at atmospheric pressure. Fuel preheat of similar to 100 K in the 0-g lam inar jet diffusion flames is found to reduce soot loadings in the annu lar region, but causes an increase in soot volume fractions at the cen terline. In addition, fuel preheat reduces the radial extent of the so ot field in 0-g. In 1-g, the same fuel preheat levels have a more mode rated influence on soot loadings in the annular region, but are also s een to enhance soot concentrations near the axis low in the flame. The increased soot loadings near the flame centerline, as caused by fuel preheat, are consistent with the hypothesis that preheat levels of sim ilar to 100 K enhance fuel pyrolysis rates. The results show that the growth stage of particles transported along the soot annulus is shorte ned both in 1-g and 0-g when elevated fuel temperatures are used. (C) 1998 by The Combustion Institute.