Experimental investigation of injection strategies on particle emission characteristics of Partially-premixed low temperature combustion mode

•The total number concentration decreases as the injection timing is advanced or delayed.•The total number concentration is obviously decreased with the increase of the pilot injection fuel ratio.•The peak values of the number concentration and mass concentration decrease as the pilot injection timing is advanced. Compared with the traditional combustion mode, Partially-premixed combustion (PPC) mode can reduce the particulate emissions. However, the particulate emission characteristics of this strategy do not have a clear conclusion. Based on a 4-cylinder turbocharged diesel engine, this paper aims at studying the influence of the fuel injection timing, injection pressure and the pilot injection to the engine combustion and emission characteristics under the condition of single-injection and split-injection PPC mode respectively. The results show that the early-injection PPC under single-injection strategy can reduce the number, mass and GMD of particles obviously. Increasing the injection pressure reduces the number concentration of particulates of the accumulation mode, but increases the number concentration of the nucleation mode. The total number and mass concentration reach up to the peak with the pilot injection timing is −25 °CA ATDC. The concentration decreases slightly with the advance of pilot injection timing. With the application of the pilot injection strategy, the peak values of the number concentration and mass concentration occur in the accumulation mode region. The NOx emission is higher in the early-injection PPC mode under the single-injection strategy. By contrast, the split strategy can control PM and NOx emissions simultaneously.