Impingement of injected fuel spray against the cylinder liner (wall wetting) is one of the main obstacles that must be overcome in order for early injection Homogeneous Charge Compression Ignition (EI HCCI) combustion. In the strategies to reduce or prevent wall wetting explored in the past, limiting the spray cone angle was proved to be a useful approach.
This paper is presented to study the effect of the spray cone angle on the mixture formation, particularly the region near the cylinder wall (wall wetting region), and CO/Soot emissions of an EI HCCI diesel engine. Three-dimensional modeling was performed in AVL FIRE code. The calculation grid was divided into three regions which were defined as the combustion chamber region, the wall wetting region, and the central regions. The history of the CO/soot mass of each region and the equivalent ratio/temperature (φ-T map) of wall wetting region were analyzed. In addition, a parameter named Mixture Homogeneous Index (MHI) was introduced to evaluate the quality of fuel/air mixture.
Conclusions drawn from the simulation suggested that wall wetting region contributed most to the total engine-out soot /CO emissions. The spray cone angle directly controlled the mixture formation and soot /CO emissions of the wall wetting region. Using narrow spray cone angle injector could reduce the wall film formed in the early injection period, further enhancing the homogeneity of the mixture in wall wetting region. This promoted the oxidation of soot and CO and improved the emission level of EI-HCCI diesel engine.