Combustion and emission characteristics of a lateral swirl combustion system for DI diesel engines under low excess air ratio conditions

In order to improve the utilization of air in the cylinder, decrease the thermal load and improve the emission performance of diesel engines, a new lateral swirl combustion system (LSCS) has been proposed in this study. An experimental investigation of the LSCS at various excess air ratios was conducted using a 132 mm single-cylinder direct injection (DI) engine. The experimental results indicate that, compared to a double swirl combustion system (DSCS), the LSCS achieves better fuel consumption and lower soot emissions. The fuel consumption was decreased by 4–5 g/(kW h) at each excess air ratio, corresponding to a reduction of about 1.13–2.8%. The decreasing trend of soot formation was also clear, with a significant reduction in the range of 63.4–70.8%. The LSCS also showed excellent performance under an excess air ratio of 1.3–1.6. At an excess air ratio of 1.3, the brake-specific fuel consumption (BSFC) of the LSCS was 228 g/(kW h), the soot emission level was 1.1 Filter Smoke Number (FSN) and the exhaust temperature was about 560 °C. Related numerical research on the impact of in-cylinder fuel/air equivalence ratio, in-cylinder temperature and in-cylinder velocity of the DSCS and the LSCS was performed, and the results show that a large proportion of the fuel/air diffusion was at the bottom of the chamber in the LSCS (away from the cylinder head). The lower concentration of the fuel/air mixture near the cylinder head in the LSCS had a positive effect and reduced the thermal load so that less engine heat was taken away by the cooling water in the water jacket of the cylinder head. Due to the lower thermal load and higher efficiency, the exhaust temperature of the LSCS was higher than that of the DSCS. The higher exhaust temperature had a positive influence on soot oxidation, which caused the soot decrease in the LSCS. It is suggested that the LSCS, with its excellent fuel consumption and low soot emission, has better application prospects in diesel engines, than the DSCS under a low excess air ratio.