Simulation Study on the Impact of Injection Strategies on the Performance of Methanol–Gasoline Dual-Fuel Engines

Methanol is favored for its excellent physicochemical properties, becoming an ideal alternative fuel for engines. Adopting a dual-fuel injection mode of methanol port injection and gasoline direct injection (MPI + GDI) allows for more flexible injection strategies, enhancing the engine’s power, efficiency, and emission performance. However, observing the processes of fuel injection, atomization, mixing, flow, and combustion in real engine cylinders is challenging, and controlling the fuel–air distribution and turbulence before engine ignition is difficult. Therefore, after validating the simulation model through optical engine bench experiments, this study investigated the performance and emission characteristics of MPI + GDI engines under various injection strategies. The results indicate that delaying the GDI injection timing decreases the uniformity of the fuel–air mixture and reduces cylinder pressure, corresponding to a retarded crank angle. Increasing GDI injection pressure enhances the fuel–air mixing, especially when the injection timing is later. Employing secondary injection and increasing the proportion of the second injection lead to poorer fuel–air uniformity in the cylinder, a decrease in peak pressure value, reduced nitrogen oxides (NOx) emissions, and a gradual increase in carbon monoxide (CO) and total hydrocarbons (THC).