Performance of large-bore methanol/diesel dual direct injection engine applying asymmetrical diesel nozzle strategies

The different schemes. (Blue sprays for diesel ignition, white sprays for methanol). [Display omitted] •An asymmetric pilot diesel nozzle that can effectively utilize ignition energy was proposed.•Optimized pilot nozzle strategy achieved rapid ignition and complete combustion of methanol.•A methanol substitution rate of 95% was realized in a large-bore 4-stroke engine.•IMEP was increased by 1.75 %; Burn efficiency was increased by 2 %; Pmax was decreased by 1 MPa.•HC emission was reduced by 97% without NOX emission increasing. The application and promotion of methanol fuel in internal combustion engines is of great significance to energy and the environment. The methanol/diesel dual direct injection, with its high methanol substitution rate (MSR) and low fuel consumption, has been receiving increasing attention. Due to the high proportion of methanol, the ignition energy of pilot diesel must be fully utilized. Otherwise, problems like higher hydrocarbon (HC) and carbon monoxide (CO) emissions, low burn efficiency, and even misfires will limit the improvement of thermal efficiency and MSR. On this account, the current study creatively proposed a unique solution of asymmetrical diesel nozzle, including inconsistent hole diameter schemes and unilateral hole nozzle schemes. To optimize the scheme of diesel nozzle structure, installation site, hole diameter, and injection angle, the numerical simulation method was applied to accurately predict the combustion and emission characteristics of the large-bore medium-speed methanol/diesel dual fuel engine. The results show that the asymmetric diesel nozzle can improve the ignition energy for methanol and maximize the ignition effect of diesel. In addition, the scheme of unilateral nozzle hole is more efficacious in promoting the rapid combustion of methanol, through which the combustion duration is significantly shortened. The engine output is increased by 3.1%, and burn efficiency (the ratio of the total heat released to the total calorific of the fuel injected into the cylinder) is increased by 2%, while the emission of HC decreased by more than 90% compared with the traditional symmetrical diesel nozzle. Furthermore, there is an optimal range for the installation position and injection angle design of the diesel fuel nozzle with unilateral holes.