Experimental investigation of effects of super high injection pressure on diesel spray and induced shock waves characteristics

Modern diesel engines employ higher injection pressure in the common-rail injection system that utilizes high-speed fuel jet to achieve rapid fuel-air mixing for spray atomization improvement. However, the spray characteristics under super high pressure are not well understood. To provide more information on spray characteristics, both the macro- and micro-characteristics of spray have been investigated under super high pressures (up to 300 MPa) via an experimental method. The spray penetration and spray cone angle were measured using a high speed camera and the microscopic characteristic of Sauter mean diameter (SMD) was obtained via Malvern Spray Tec to analyze the influence of super high injection pressure on diesel spray atomization. Induced shock waves were captured using a Schlieren system when the spray tip velocity was greater than the local sound velocity accompanied by diesel spray. The results obtained show that higher injection pressures lead to larger spray velocities and a smaller shock wave angle if it exists, with connection between spray and shock waves, and generates a smaller SMD with less decreasing amplitude. Additionally, two different types of leading shock waves-bow and oblique shock wave appeared sequentially with increasing injection pressure.