Research on the Influence of Miller Cycle on Mixture Formation in GDI Engine under Cold Start

In this paper, a gasoline direct injection(GDI)engine is selected for bench test and one-dimensional simulation to provide reliable boundary and initial conditions for the 3D simulation. Miller cycle valve lift lines for early intake valve closing(EIVC)is designed, and the Miller cycle engine model is established and verified to examine the influence of the Miller cycle on the development of wall film and the formation quality of spray field in low temperature environment. Research shows that the mass of the wall film in the Miller cycle engine is greater than that of the original engine at the end of the intake stroke. During the entire intake and compression strokes, most fuel film including the thick fuel film was concentrated in the piston pit. The spreading area of the fuel film on the top of the piston in the EIVC75 Miller cycle increased significantly, and the thickness of the fuel film around the pit decreased clearly. In the middle-late stage of the compression stroke, due to the slow dissipation of turbulent kinetic energy in the cylinder, the evaporation of the fuel wall film is promoted. At the time of ignition, the wall film mass of EIVC60 and EIVC75 decreased by 28% and 48% respectively, which can effectively avoid the 'pool fire' phenomenon. Moreover, the concentration field of the original engine is greatly different from that of EIVC60 and EIVC75. The equivalence ratio near the original engine spark plug is about 0.8, while that of a mixture suitable for ignition near the spark plug of the Miller cycle engine is 1.1-1.2。. © 2022 Xi'an Jiaotong University. All rights reserved.