EXPERIMENTAL STUDY OF DIESEL SPRAY AND COMBUSTION PROCESSES UNDER SPLIT INJECTION STRATEGY; PHENOMENA OBSERVATION FROM LATERAL SIDE OF A TWO-DIMENSIONAL PISTON CAVITY IN A RAPID COMPRESSION AND EXPANSION MACHINE

The effect of split injection on mixture formation and combustion process was investigated in a rapid compression and expansion machine (RCEM). A two-dimensional (2D) piston cavity, which was designed as the cross section of a reentrant piston, was used to observe the in-cylinder information from the lateral side. The experiments were conducted at injection pressures of 80 MPa and 120 MPa. High-speed shadow method was applied to investigate the spray development, mixture formation, ignition location, and soot generation in the cylinder. The results showed that fresh oxygen and part of oxidized soot were involved in the burned pilot mixture with main spray injection, which was beneficial to reducing the soot particles. Furthermore, split injection accelerated the spray mixture development resulting from the air entrainment, and the longer interval led to more uniform mixture distribution, which was beneficial to improving the combustion process while suppressing the soot generation. This research provides a detailed investigation on diesel spray and combustion process and demonstrates that the impinging spray has a significant effect on the combustion process.