Injection Strategy to Enhance Mixture Formation and Combustion of Fuel Spray in Diesel Engine 2018-01-0241

Increasing the injection pressure and splitting the injection stage are the major approaches for a diesel engine to facilitate the fuel-air mixture formation process, which determines the subsequent combustion and emission formation. In this study, the free spray was injected by a single-hole nozzle with a hole-diameter of 0.111 mm. The impinging spray, formed by a two-dimensional (2D) piston cavity having the same shape as a small-bore diesel engine, was also investigated. The injection process was performed by both with and without pre-injection. The main injection was carried out either as a single main injection with injection pressure of 100 MPa (Pre + S100) or a split main injection with 160 MPa defined by the mass fraction ratio of 3:1 (Pre + D160_3-1). The tracer Laser Absorption Scattering (LAS) technique was adopted to observe the spray mixture formation process. The ignition delay/location and the soot formation in the spray flame were analyzed by the two-color method. Two ambient gas strategies, 21% and 15% O₂, were adopted in the combustion process to investigate the effect of O₂ concentration. The experimental results revealed that the vapor distribution of split injection was much more homogeneous than that of the single one. High soot concentration and low temperature appeared near the cavity wall region under the three injection strategies. The second main injection caught up with the previous injection’s flame, which deteriorated the combustion and resulted in higher soot generation. Low O₂ concentration increased the soot mass and resulted in longer combustion duration. However, interestingly, it deteriorated the soot formation process through the soot index.