Numerical Optimization of the Piston Bowl Geometry and Investigation of the Key Geometric Parameters for the Dual-Mode Dual-Fuel (DMDF) Concept under a Wide Load Range 2022-01-0782

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 low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization. In order to meet the peak pressure rise rate (PPRR) limit at high load, the integrated compression ratio (CR) of 12.5 is employed over the whole load range, which sacrifices the fuel economy to some extend at low and mid load. The deteriorated combustion and thermal efficiency resulted from the decreased CR at low load can be compensated by increasing intake temperature. Among the three geometric parameters, the bowl width plays a more important role in managing the heat transfer losses and the corresponding indicated thermal efficiency (ITE) in contrast to the axis depth and bowl depth. Moreover, the piston bowl with a more sunken profile can lead to a more strengthened local flow field intensity, which is beneficial for the oxidation of the incomplete combustion products and soot emissions. Meanwhile, the wall impingement, which is affected by the bowl width, also plays an important role in the CO and soot emissions.