Effect of oxygen concentration on the split injection combustion process of diesel spray injected into 2D piston cavity

The exhaust gas recirculation (EGR) technique effectively reduces NOx emissions, and the split injection can lower engine emissions. There is little research on the formation and oxidation of soot during fuel combustion by combining EGR and split injection. Therefore, the effect of oxygen concentration on the split injection strategies' flame characteristics was investigated by analyzing the integrated KL factor, the mean flame temperature, and the soot evolution. The experiment combines various conditions of single main injection, double main injection, high injection pressure, and low injection pressure, with pre-injection and without pre-injection, to discuss the influence of oxygen concentration on combustion characteristics. The 2D piston cavity has been used to form the impingement spray flame, and the two-color method has been used to analyze the combustion characteristics. Results reveal that there will not be fuel accumulation along the cavity groove between the first and the second main injection under low oxygen concentration with pre-injection conditions. Pre-injection reduces the soot oxidation rate under double main injection with low oxygen concentration. The ignition timing of the first main injection under double main injection with pre-injection conditions occurred in advance, even under low oxygen concentration conditions. The effect of oxygen concentration on the total flame area is not as significant as that of pre-injection or without pre-injection conditions. Considering all conditions, split injection (D160_50:50) without pre-injection has higher soot oxidation rate under 15% O2. The injection strategy (S160) without pre-injection can minimize soot and NOx emissions at a concentration of 15% O2.