The effect of air and exhaust dilution ratios on the characteristics of ultra-fine particulate matter (PM) and combustion process in different combustion modes at low loads were investigated based on experimental and numerical simulation in this study. The combustion modes included partially premixed compression ignition (PPCI), diffusion combustion (DC), and modulated kinetics combustion (MKC). The air and exhaust gas dilution ratio varied from 0 % to 40 % and 0 % to 55 % respectively. Additionally, the effect of dilutions and combustion modes on PM characteristics is precisely analyzed by computational fluid dynamics. The NOx and Soot emission are reduced in PPCI and DC mode of combustion with the increase of air and exhaust gas dilution rate. However, NOx emission is decreases while Soot is increases in MKC mode. The concentration of particulate number increases in case of both PPCI and DC mode and achieved highest value as 3.3 × 10
