The utilization of low- and zero-carbon fuels in internal combustion engines is gaining increasing interest. In marine engine applications, the co-combustion of methane and ammonia has emerged as a promising strategy for reducing carbon emissions. In this work, a chemical kinetic mechanism for n-heptane/methane/ammonia blended fuel was developed and validated. Using this mechanism, sensitivity and chemical kinetic analyses were performed to explore the ignition characteristics of the fuel mixture. The results indicate that at an initial temperature of 1000 K, reaction R152 (C7H15-2 = CH3 + C6H12) exerts the strongest inhibiting effect on ignition. C7H15-2 is a major low-reactivity intermediate generated during n-heptane decomposition, and the accumulation of such intermediates contributes to the negative temperature coefficient (NTC) behavior. A cross-reaction between CH4 and NH3, R111 (CH4 + NH2 = CH3 + NH3), was identified, which impedes the smooth progression of oxidation. Elevated temperatures, oxygen-rich conditions, and higher ammonia blending ratios promote the formation of NO. The production of N2O is primarily governed by reaction R105 (NH + NO = N2O + H), whose rate increases with the NH3 molar fraction. Consumption of N2O occurs mainly via reactions R92 (N2O + H = N2 + OH) and R94 (N2O (+M) = N2 + O (+M)), both of which occur later than its formation through R105, indicating that N2O consumption is more sensitive to temperature.
Rui et al. (Wed,) studied this question.