Numerical Study on the Effects of Ammonia on NOX, PAH and Soot Emissions in Ethylene and n-Heptane Flames

The overall objective of this research is to examine effect of ammonia addition on NOx and soot emissions in ethylene and n-heptane flames. In sooting ethylene flames, the chemical and dilution effect of ammonia on NOx and soot formation is investigated. The global effect of ammonia substitution on NOx and soot emissions n-heptane is established. Simulations have been performed for non-premixed flames burning ethylene and n-heptane in a counterflow configuration. A validated detailed kinetic model with 13847 reactions and 372 species has been used in the counterflow flame simulations. Results indicate that the addition of ammonia leads to decreased formation of acetylene and propargyl, PAH and soot but an increase in NO, in both flames. Further ammonia or argon/ethylene flames were subjected reaction path analysis and rate of production analysis to identify and determine the chemical and dilution effects. Results indicate a 50% reduction in the rate of reactions contributing to PAHs formation and 2 times increase in reactions responsible for NO formation. Furthermore, to determine the effect of ammonia substitution or blending of diesel, an extensively used single component diesel surrogate n-heptane is studied. Results indicate similar to ethylene flames PAH and soot emissions decrease significantly. No significant on flame structure or heat released is observed with ammonia addition up to 50% but a moderate decrease in flame temperature and shift in flame is observed for 75% and 90% cases. NOx emissions increased significantly due to addition of ammonia which is consistent with ethylene flames. Therefore, this study serves a basis for further engine studies for n-heptane and ammonia blends at different operating conditions.