A Study of Pre-Injection Effects on Combustion, Emissions, and Performance of Methanol–Ammonia Dual-Fuel Engines

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 NOX, 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, NOX and soot emissions can also be significantly reduced. Compared with low pre-injection quantities, by using high pre-injection quantities, soot and NOX 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 NOX 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 NOX emissions can be reduced by 30.31%.