Mixing and combustion mechanisms within lateral swirl combustion system (LSCS) in a DI diesel engine

The fuel diffusion around the combustion chamber wall is the key to affecting the engine performance. The current enveloping combustion systems (e.g. ω combustion systems) mainly utilize the air in the radial direction of the combustion chamber along the spray track. In these systems, since the combustion chamber wall only envelops the spray without obvious guiding effect, it will cause difficulty in the fuel diffusion around the chamber wall and deteriorate the combustion. On the contrary, the LSCS, as a guiding combustion system, could effectively improve the diffusion around the chamber wall. Therefore, it is necessary to further understand the mixing and combustion mechanisms of the LSCS. In this study, the spray and combustion characteristics of the wall-impinging jet in the lateral swirl (LS) combustion chamber were investigated in a constant-volume combustion vessel through the high-speed photography. These characteristics were compared between the ω and LS combustion systems through the image processing and the two-color method. The results show that the spray process in the ω combustion system contains free jet and wall jet, while the spray process in LS combustion system contains free jet, formation of LS, and LS & intervening wall jet after the separation of jet head from the convex edge. The LSCS forces the fuel spray to swirl along the circumference of the combustion chamber. As a result, it could strengthen the diffusing and mixing process, and avoid a large quantity of fuel burning near the wall to form a thermos constraint. The LSCS could improve the distribution of the air-fuel mixing and consequently accelerate the combustion and reduce the soot emission through the guiding effect of convex edge on the wall jet.