Computational optimization of the piston bowl geometry for the different combustión regimes of the dual-mode dual-fuel (DMDF) concept through an improved genetic algorithm

Abstract

[EN] Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at various loads. An improved genetic algorithm was introduced in this study, which is superior in searching for the global optimal solutions. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized at the various loads. The results show that the piston bowl geometry optimization can further improve the thermal efficiency with 1.4%, 4.4%, and 1.4% percentage points for the low, mid, and high loads, respectively. An indicated thermal efficiency up to 51.8% can be realized at mid load. Meanwhile, for all the optimal cases, NOx and soot emissions can meet the Euro VI limits. At low and mid loads, both the open and re-entrant type piston bowl can be equipped, while the high load only prefers the open type piston bowl for the DMDF mode. The re-entrant type or deep piston bowls are superior in organizing strong in-cylinder flow, which is beneficial for the fuel/air mixing. The open type or shallow piston bowls are helpful for reducing the heat transfer losses owing to the less heat transfer surface area. Furthermore, a correlation analysis was conducted to investigate the sensitivity of engine performance to the piston geometric parameters and injection parameters. It is concluded that the fuel injection event becomes more important for managing the engine performance as load increases. Among the injection parameters, the influence of the fuel injection timings and injection pressure on engine performance is more obvious. The piston geometric parameters play more significant roles in the heat transfer losses than the injection parameters for all loads. Among the geometric parameters, the most influential parameters are the width and open extent of the piston bowl. The heat transfer loss energy fraction can be well decreased with a wider and more open piston bowl.