Effects of Rounding-off Inlet Hole in Fuel Nozzle on Spray and Combustion Characteristics under High-Pressure and High-Temperature

摘要

Experiments were performed to clarify the effects of rounding-off inlet hole of nozzles on spray and combustion characteristics for six pieces, two types injection nozzles with and without rounding-off. Marine diesel fuel oil was used in every test, the matrix of experimental conditions included ambient temperature from 470K to 1000K, ambient pressure from 3MPa to 7MPa, fuel pump revolution was set at two fixed value of 150rpm and 250rpm and position of fuel pump rack of 10, 20 and 30 notches. High resolution, high speed video camera possible to take up to 12000 frame per seconds with extension trigger was adopted, with available software, imagine pictures were analyzed synchronized on the same screen, it revealed that with rounding off nozzle at low pressure and low temperature of ambient condition ignition starts early than without rounding-off nozzles. At supposed conditions of two-phase (liquid and gases) flow inside the nozzle, a commercial CFD engine simulation software program was also adopted to calculate and visualize cavitations. Turbulence phenomena occurred at Inlet hole area of fuel injector nozzle and calculated velocity distribution along axis of nozzle for two typed of nozzle with and without rounding-off was obtained by turbulence and injection spray output. The geometry of two nozzles is symmetrical and exactly the same except the radius of curvature of inlet hole. Inlet and outlet boundary condition were defined for three cases 120MPa, 72 MPa and 36MPa corresponding to condition of the experiments. It is found that the velocity distribution along the axis of rounding-off nozzle was higher than without rounding-off ones. The difference in the higher velocity distribution can be explained by term of the cavitation generated In without rounding-off Injection nozzle. Experiment results validated, the effects of rounding-off inlet hole nozzle not only to reduces cavitations, turbulence, increase effective flow area, but also potentially improve combustion process at low ambient temperature that corresponding to low load condition of diesel engine. In contrary, at condition of high temperature and fuel pump rack of 20 and 30 notches, ignition delay of two type nozzle were similar.