The fuel-air mixture formation and combustion of an off-road direct-injection diesel engine with split injection were computationally investigated

and the effects of squish and swirl flows on the equivalence ratio distribution and combustion of the fuels from both pilot and main injections were analyzed. The results show that the squish flow tend to transport the pilot-injected fuel vapor into the piston bowl when properly increasing the interval between pilot and main injections(20° in crank angle) and a moderate swirl flow(from 1.5 to 2.0) can shift the pilot injection sprays towards the regions between two adjacent main-injection sprays. Remarkably

both of the two effects can reduce the overlap of the pilot and main injections

and the heat released from the pilot injection combustion can further accelerate the mixing and combustion processes of the main injection. An optimal pilot injection strategy together with a proper swirl ratio can increase engine power with reduced soot emissions

although the NOx emissions will be unfavorably increased.