Prediction of wall impingement in a direct injection spark ignition engine by analyzing spray images for high-pressure injection up to 50 MPa

This study was performed to analyze the wall impingement and fuel film formation in a DISI engine with injection strategies using image-based analysis and CFD. The direct injection engine uses a high-pressure injection strategy to improve the homogeneity of the air-fuel mixture, so the spray behavior was analyzed by spray visualization for various injection pressures, and the wall impingement was predicted for various engine operating conditions based on the acquired images. The mass distribution of the injected fuel was calculated using the injection profiles and the spray image, and the amount of fuel that impinges on the piston and wall (i.e., the geometric boundaries of the cylinder) was calculated using data from the spray behavior for various engine operation conditions such as load and engine speed. The image-based analysis was limited to understanding the influence of the injection strategy on the droplet behavior after wall impingement of the fuel spray. Therefore, CFD using KIVA 3 V code was additionally conducted to analyze the effects of the injection strategies on wall film formation and droplet rebounding reflecting in-cylinder conditions. In the early- and late-injection conditions, the initial piston position is high, and most of the injected fuel impinges on the piston. As the injection pressure increases, the injection timing at which wall impingement occurs is advanced because of the rapid spray development. The results of the 3D analysis for the temperature and the intake flow in the engine cylinder showed that both the wall impingement and the fuel film were reduced as the injection pressure increased because the fuel evaporation increased due to improved atomization.