A comprehensive experimental and kinetic modeling study of laminar flame propagation of ammonia blended with propene

Enhancement of ammonia reactivity is crucial for potential applications of ammonia as an engine and gas turbine fuel. A common strategy for improving ammonia's poor reactivity is blending it with more reactive fuels like hydrogen and methane. However, fundamental studies of ammonia combustion with higher hydrocarbons and key intermediate oxidation species of higher alkanes such as propene do not exist. Thus, this work presents an effort to study the laminar flame propagation of ammonia blended with propene. Laminar burning velocity (S_L) of NH₃/C₃H₆/air mixtures was measured at 298 K, pressures up to 5 bar, equivalence ratios of 0.7 to 1.3, and various propene to ammonia ratios (i.e.,% propene to ammonia mole fraction, x_C3H6 = 10 to 50) in a high-pressure spherical propagating flame vessel. A kinetic model was developed based on our previous work to characterize the combustion behavior of NH₃/C₃H₆/air mixture. The model reasonably agrees with the experimental data and follows the observed trends very well. The results showed that blending NH₃ with C₃H₆ positively enhanced S_L of NH₃ by promoting the formation of key radicals e.g., O, OH, and H. Relative to a neat ammonia/air mixture, co-firing ammonia with propene leads to a reduced pressure dependence of the laminar burning velocity. However, the reaction H + O₂(+M)=HO₂(+M) leads to strong pressure dependency of lean NH₃/C₃H₆ mixtures compared to rich mixtures. The model reveals that besides fuel-NO coming from NH₃, prompt NO also actively contributes to NO formation. It is seen that N₂O formation is significantly suppressed with increasing pressure or increasing C₃H₆ content in the fuel blend. In contrast to NO and N₂O, NO₂ concentration increases slightly with an increase in pressure. The reported experimental data and model will be useful in understanding the interaction between NH₃ and alkenes.