The combustion and emission characteristics of a multi-swirl combustion system in a DI diesel engine

In this study, the authors developed a new multi-swirl combustion system (MSCS) and investigated its combustion and emission characteristics. The MSCS combines the structural features of a double swirl combustion system (DSCS) and a lateral swirl combustion system (LSCS) and utilizes the arc structure of the MSCS to lead fuel to (1) form multi-swirls in both a longitudinal and lateral direction, (2) accelerate the fuel/air mixture and (3) improve the combustion process in a diesel engine. An experimental study and simulation analysis was used to verify the MSCS combustion and emission characteristics. In the experimental study, tests at various speeds were conducted using a single-cylinder diesel engine. The experimental results, including the brake specific fuel consumption (BSFC), soot emission, NOx emission and in-cylinder pressure were recorded and compared with results from a DSCS that was operated under the same condition. In the simulation, the fuel spray process was studied using AVL-Fire. The fuel velocity profile and the fuel/air equivalent ratio distribution were studied to verify the formation of multi-swirling fuel in the combustion chamber. The experimental results show that the BSFC of the MSCS was lower by 4–5 g/(kW h), and the soot emission was lower by about 60% in comparison to the results from the DSCS. The simulation results show that the fuel formed two longitudinal swirls in opposite directions after touching the circular ridge, and the fuel in the outer chamber formed two swirls in lateral space after touching the convex edge. This multi-swirl enlarged the diffusion space of the fuel in both the inner and outer combustion chamber and accelerated the formation of the fuel/air mixture, which led to a decrease in soot emission and fuel consumption from the MSCS.