Combustion and Particulate Matter Emission Characteristics for Diesel Engine Run by Partially-Premixed Low-Temperature Combustion Mode 2017-01-2398

Partially-premixed low-temperature combustion avoids the soot and NOx generation area on the Ф-T diagram to reduce both engine NOx and soot emissions. Compared with the HCCI combustion mode, partially-premixed combustion (PPC) has better combustion controllability. The purpose of controlling the combustion phase can be achieved by adjusting injection timing and strategy. Based on a 4 cylinder turbocharged diesel engine, this paper aims at investigating the influence of injection strategy to the engine combustion and emission formation under the condition of single injection and split injection PPC strategy respectively, in which the primary purpose focus on the emission characteristics of particles. Results show that the early-injection PPC formed by single injection can reduce the quantity, quality and geometric mean diameter (GMD) of particles obviously. However, when the injection timing is too early, the number of particles will rise to the level as the traditional mode since the concentration of particulate matter in the nucleation region increases dramatically. The pilot injection strategy can reduce soot emission significantly, while at the same time, the concentration of nucleation mode particles remains stable, which differs from single early injection PPC. However, if the timing of the pilot injection advanced to a certain value, the quantity, quality and GMD of particles are almost unchanged. Increasing the proportion of pilot injection fuel to form a higher proportion of premixed combustion, both the quantity and quality of particles will decrease, GMD will undergo an increase-decrease process. CO and HC emissions are very low under the early injection PPC. While in the pre-injection strategy, the fuel burning rate is low and many intermediate products generate, so the CO and HC emission will increase as the pre-injection fuel ratio increases and pre-injection timing advances.