Objective To improve the combustion, performance, and emission of high-power marine engines, diesel micro-injection fuel injection with methanol ignition is adopted to study the in-cylinder combustion and emission characteristics of the engine.

Methods A three-dimensional simulation model of a diesel micro-injection pilot-ignition methanol engine is established based on an ACD320 high-power marine medium-speed diesel engine to study the effects of injector parameters (number of spray holes and methanol spray angle γ) on the combustion performance and emission characteristics of a marine large-bore methanol engine.

Results The results of the study show that with the increase in the number of nozzles, the in-cylinder methanol atomization is better, so the in-cylinder work mass mixing is more adequate, which leads to the advancement of CA50 and the shortening of the combustion duration period, obtaining higher indicated thermal efficiencies and better fuel consumption rates, and at the same time contributing to the reduction of Soot emissions, but it will lead to the elevation of NOx emissions. Moreover, as the methanol spray angle γ increases, the indicated thermal efficiency increases, and better fuel economy and lower Soot emission are obtained. When the methanol spray angle is located in the diesel spray angle (γ>60°), the flame propagation speed in the cylinder is faster, the indicated thermal efficiency is larger, and the fuel combustion is more adequate, to obtain the lowest emission of carbon smoke and the optimal fuel consumption rate.

Conclusions Marine diesel micro-injection ignition methanol to promote the fuel combustion rate in the cylinder, improve the indicated thermal efficiency, to obtain better fuel economy. Analyze the effects of the number of spray holes and the angle of methanol spray on the combustion and emission in the engine cylinder, and provide a theoretical basis for the engine injector arrangement.