Investigation of Injection Strategy on Combustion and Emission Characteristics in a GDI Engine with a 50 MPa Injection System

A DMS500 engine exhaust particle size spectrometer was employed to characterize the effects of injection strategies on particulate emissions from a turbocharged gasoline direct injection (GDI) engine. The effects of operating parameters (injection pressure, secondary injection ratio and secondary injection end time) on particle diameter distribution and particle number density of emission were investigated. The experimental result indicates that the split injection can suppress the knocking tendency at higher engine loads. The combustion is improved, and the fuel consumption is significantly reduced, avoiding the increase in fuel pump energy consumption caused by the 50 MPa fuel injection system, but the delayed injection increases particulate matter emissions. In terms of particulate matter emissions, increasing the excess air ratio, advancing direct fuel injection, increasing fuel injection pressure, and delaying ignition timing will all lead to the reduction of the particulate matter emissions. The emission results also demonstrate that an increase in fuel injection pressure from 35 MPa to 50 MPa significantly reduces the particle number (PN) of all particle size segments, which has a significant effect on reducing the number of accumulated particles, and the PN concentration is reduced by more than 20%. At 1500r/min 15 bar working condition, triple injection strategy with 50MPa injection pressure, the PN is reduced by 41% compared with the base engine, and fuel consumption is increased by 0.8%. The characteristics of gas emissions are mainly to provide guidance for the selection of injection strategy to avoid excessive deterioration of gas emissions while optimizing particulate matter emissions and fuel consumption. The optimal particulate emission characteristic is obtained at the last injection end timing of 90°CA.