Visualization experiment and simulation study of impinging spray and impinging flame in a new wall-guided combustion system

As a typical wall-flow-guided combustion system, the double swirl combustion system (DSCS) uses its circular ridge to promote fuel spray diffusion in combustion chamber and improve fuel-air mixing. However, with increasing engine load, DSCS exhibits limited capability to further enhance fuel-air mixing. This paper proposes an improved-DSCS (I-DSCS). In I-DSCS, the circular ridge is retained but relocated to the side wall of combustion chamber. The design objective of I-DSCS is to further enhance fuel spray diffusion by reallocating the spatial distribution of the inner and outer chambers and redistributing the fuel spray proportion within the inner and outer chambers.To verify the I-DSCS design and demonstrate its effectiveness in enhancing fuel-air mixing, visualization experiments were conducted in a constant volume combustion vessel with two-dimensional DSCS and I-DSCS combustion chamber cavities. Using schlieren photography and direct photography methods, the impinging spray and impinging flame characteristics were studied under various ambient densities and fuel injection pressures. Simulation studies were performed to analyze impinging spray characteristics under in-cylinder conditions corresponding to various engine loads. Experimental results indicate that the optimal fuel spray impingement position in I-DSCS is the circular ridge, which is consistent with its wall-flow-guided design. Compared with the mature DSCS, in I-DSCS, the impinging spray exhibits increased diffusion magnitude, while the impinging flame exhibits enhanced combustion intensity, shortened combustion duration and reduced soot production level. Simulation results show that, due to more intense turbulent mixing, the impinging spray in I-DSCS achieves better fuel-air mixing quality and more uniform mixture distributions.