Pressure dependence of sooting characteristics of m-xylene and n-octane doped laminar methane diffusion flames from 2 to 10 bar

Abstract

The work reported here contributes to a wider effort that focuses on the issue of whether single ring aromatics and their same carbon number alkane counterparts have the same pressure dependence of their sooting characteristics. Influence of doping methane base fuel with either m-xylene or n-octane in laminar high-pressure co-flow diffusion flames was studied from 2 to 10 bar pressure in current work. Two liquid hydrocarbons added to the base fuel methane contributed 3% of the total carbon mass flow in the fuel stream, which was kept fixed at 0.524 mg/s at all pressures considered, to have tractable measurements. The methane flames doped with either m-xylene or n-octane were stabilized on a co-flow diffusion burner installed inside of a high pressure combustion chamber with optical access. Temperatures and soot volume fractions were inferred from spectrally-resolved measurements of soot radiation. Line of sight soot emission intensities were inverted at each measurement plane along the flame axis to obtain radially-resolved temperature and soot volume fraction. Soot yields, calculated from soot volume fractions, of m-xylene doped flames were found to be higher than those of n-octane doped flames in the pressure range of 2–10 bar; however, the ratio of soot yields of m-xylene to n-octane decreased with pressure, from 2.9 at 2 bar to 1.2 at 10 bar. This finding implies that m-xylene and n-octane, both with eight carbons in their molecular structure, do not have the same sooting propensity with increasing pressure; m-xylene’s pressure dependence is weaker than that of n-octane within the pressure range of 2–10 bar.