The implementation of methanol-ammonia dual-fuel engines has the potential to contribute to a reduction in carbon emissions in the environment. The present study employs numerical simulations of the methanol-ammonia dual-fuel engine to investigate methanol direct injection pre-injection strategies. The impact of pre-main injection time interval and pre-injection quantity was investigated on output power, output torque, cylinder pressure and exhaust emissions such as NO_X, HC, CO, and CO₂. The results show that compared with the single methanol injection strategy, increasing the pre-injection strategy can effectively reduce soot emissions. Under certain pre-injection conditions, NO_X and soot emissions can also be significantly reduced. Compared with low pre-injection quantities, by using high pre-injection quantities, soot and NO_X emissions can be reduced by 36.91% and 35.31%, respectively. Under high pre-injection quantities, increasing the pre-main injection time interval can also significantly reduce NO_X emissions. Compared with the single methanol injection strategy, the pre-injection strategy leads to an increase in cylinder pressure peak and an advance in peak timing. As the pre-main injection time interval increases, both output power and output torque decrease. It is found that when the pre-injection quantity is 6 mg and the pre-main injection time interval is 25 °CA, with no substantial reduction in output power and output torque, the engine’s soot emissions can be reduced by 34.67%, and NO_X emissions can be reduced by 30.31%.

Utilizing ammonia (NH₃) as a zero-carbon alternative fuel requires a deeper understanding of its combustion characteristics, with ignition delay time (IDT) serving as a critical descriptive parameter. To investigate the effects of propane (C₃H₈) addition on NH₃ ignition at high temperatures, the ignition delay times of NH₃/C₃H₈ blends were systematically measured using a shock tube over a wide range of conditions: temperatures of 1263–2117 K, pressures of 0.14–0.5 MPa, equivalence ratios of 0.5–2.0 and propane mole fractions of 5–70%. The results indicate that propane addition significantly promotes ammonia ignition. Under stoichiometric and 1.4 atm pressure conditions, the addition of C₃H₈ to pure NH₃ reduces the ignition delay time by approximately fivefold, allowing auto-ignition to occur at a lower temperature. Furthermore, detailed chemical kinetic mechanisms from the literature were adopted for numerical simulations and validated against the newly acquired experimental data. Kinetic analysis reveals that the propane addition does not alter the main oxidation pathways of ammonia, while it triggers C-N cross-reactions at higher blending ratios (>30%). The active radicals generated during the early stages of propane oxidation accelerate H-abstraction reactions, serving as the key mechanism responsible for the shortened ignition delay times and promoted ignition.