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

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

Results With the increase in the number of nozzle, the in-cylinder methanol atomization improves and the in-cylinder work mass mixing becomes more adequate, leading to the advancement of CA50 and the shortening of the combustion duration. While this yields higher indicated thermal efficiency（ITE） and a better equivalent indicated specific fuel consumption (EISFC), as well as contributing to the reduction of soot emissions, it also causes the elevation of NO_x emissions. Moreover, as the methanol spray angle increases, the ITE increases, obtaining better fuel economy and lower soot emissions. With the optimal methanol spray angle (γ = 60°), the methanol spray is located in front of the diesel spray injection point, the flame propagation speed in the cylinder is faster, the indicated thermal efficiency is at its maximum and the fuel combustion is fuller, thereby obtaining the lowest soot emissions and most optimal EISFC.

Conclusion The results of this analysis can provide a theoretical basis for engine injector parameters.