Fuel and air mixing characteristics of wall-flow-guided combustion systems under a low excess air ratio condition in direct injection diesel engines

Highlights: • For the double swirl combustion system, spray cone angle 150° is the optimal value. • The lateral swirl combustion system has a wide spray cone angle matching ability. • Wall-Flow-Guided combustion systems performed better under a low excess air ratio. • A new method to qualitatively evaluate the mixture quality in the combustion system. -- Abstract: In this study, wall-flow-guided combustion systems (WFGCS) were analyzed with the view to improve air use efficiency, fuel economy and emission performance in direct injection (DI) diesel engines. The results of previous study show that WFGCS facilitate favorable combustion and emission performance at low excess air coefficients. To quantitatively analyze the fuel/air mixing characteristics of WFGCS under a low excess air ratio, a computational fluid dynamics (CFD) simulation method was used to measure the spray concentration distribution in a double-swirl combustion system (DSCS), lateral-swirl combustion system (LSCS) and ω combustion system (OMECS). The results show that with an excess air ratio of 1.5, WFGCS reduce the proportion of the rich mixture with an equivalence ratio between 2 and 4 and increase the combustible mixture with an equivalence ratio between 1 and 2, which is conducive to improving the combustion and emission characteristics of DI diesel engines. Therefore, WFGCS have broad application prospects in refining the fuel/air mixture and improving the air use efficiency in the combustion chamber of DI diesel engines.