On the Effects of Oxygen-Enrichment and Fuel Unsaturation on PAHs and Soot Emissions in Ethylene, Propane, and Propene Flames

摘要

A computational study is performed to characterize the effects of oxygenation on the flame structure and emissions. This is accomplished by using O_2-enriched air and N_2-diluted fuel in such a way that the adiabatic flame temperature is not materially changed. In addition the effect of unsaturation on emissions is examined. 1-D counterflow flames burning ethylene, propane, and propene are simulated with CHEMKIN-Pro, using a validated mechanism with 197 species and around 5000 reactions. As the level of oxygenation is increased, it leads to a significant reduction in PAH formation, and with additional soot oxidation in the post flame region, it provides nearly non-sooting flames, although NO emission increases. The rate of production analysis indicates that the presence of double bond promotes reactions which produce higher amounts of allyl and propargyl species, and thus higher amounts of soot precursor, benzene and pyrene. Consequently, ethylene and propene flames produce significantly higher amount of soot compared to propane flames.