Parametric Study of Enhanced Combustion Based on Nozzle Protrusion and Spray Angle of High-Power-Density Diesel Engine

The goal of high-power-density diesel engines is to enhance combustion efficiency and reduce fuel consumption, which has always been the focus of diesel engines in addressing energy and environmental challenges. A high injection pressure allows a significant amount of fuel to be injected in a short period. However, this also increases the risk of spray impingement in small-bore diesel engines. Therefore, optimizing the nozzle protrusion and spray angle to achieve appropriate spray and flame extension is crucial for complete combustion. First, the flame development characteristics of nozzle protrusions ranging from 2 to 5.5 mm were analyzed with fixed spray angles and spray impingement points, respectively. The spray impingement point was optimized by comparing the combustion quality at different spray angles. Finally, the matching of the nozzle protrusion was performed based on the corrected points. The results indicate that the flames in small-bore diesel engines possess significant kinetic energy after impingement. During its development from the piston to the cylinder head, premixed combustion remained dominant. Longer spray penetration promotes the formation of a larger flame surface, and the combination of different nozzle protrusions and spray angles can alter the adhesion of combustibles along the wall. A smaller spray angle and shorter nozzle protrusion can enhance the thermal efficiency by 3.7% and reduce the heat loss by 0.2%, respectively. This research provides valuable insights for optimizing the design of fuel injection parameters and combustion chamber shapes for small-bore diesel engines.