Computational Optimization of Syngas/Diesel RCCI Combustion at Low Load in Different Engine Size 2019-01-0573
Syngas is considered to be a promising alternative fuel for the dual-fuel reactivity controlled compression ignition (RCCI) engine to reduce the fuel consumption and emissions. However, the optimal syngas compositions and fuel supply strategies in RCCI combustion are significantly affected by engine configurations, which have not been investigated yet. In this study, by integrating the KIVA-3V code and the non-dominated sort genetic algorithm II (NSGA-II), the optimizations for a 0.477 L single-cylinder engine with shallow and wide piston bowl (engine A) and a 1.325 L single-cylinder engine with conventional omega-type piston bowl (engine B) under the syngas/diesel RCCI combustion were performed. The optimized operating parameters include the fuel-supply strategies, syngas compositions, and intake conditions. The results indicated that the single injection strategy with high premix ratio is able to achieve the high efficiency combustion in the engine A, and the injection timing is restricted around -20 °CA ATDC for the adaptable combustion phase. For the engine B with the larger displacement, the double injection with late main injection timing is necessary to improve the combustion efficiency of the near-wall syngas. Comparing with the simple syngas compositions used in the engine B, the syngas compositions are more flexible for the engine A. Under the optimal fuel supply and intake conditions, a syngas with 75% H2 and the diluent factor C of 0.8 is capable of realizing the high efficiency and moderate combustion for both the two engines, and the NOx emissions also can be controlled in a satisfactory level.
Zhen Xu, Ming Jia, Guangfu Xu, Yachao Chang