Comparison of non-fuel hydrocarbon concentrations measured in coflowing nonpremixed flames fueled with small hydrocarbons

Abstract

Centerline concentrations of twenty-nine C2 to C12 hydrocarbons were measured by extractive gas sampling combined with on-line photoionization mass spectrometry in soot-containing methane and nitrogen-diluted ethane, ethylene, acetylene, propane, and n-butane coflowing nonpremixed flames. Additional measurements were made of temperature with thermocouples and of soot concentration with laser light scattering and thermocouple particle densitometry. The fuel hydrocarbon and nitrogen flowrates were chosen such that each flame had a visible flame length of approximately 40 mm and similar soot concentration profiles. Essentially the same species were detectable in each flame, and these species are generally those that are predicted to be most thermodynamically stable under rich flame conditions. The different fuels produce widely varying ratios of C2 to C5 non-aromatic species, enough to suggest that the primary pathways to aromatic species may be different among the flames. The fuels produce relatively similar ratios of aromatic species, but the concentrations of aromatics varies considerably among the fuels, even though the soot concentrations were very similar. However, the temperatures at the onset of soot formation were similar to within 100 K.