A Study of the Air-Entrainment into a Diesel Fuel Spray

Abstract

The behavior of air-entrainment into a diesel fuel spray was studied by analyzing the air movement around a free non-evaporating diesel spray in a pressurized vessel. To measure the air movement around the spray, a density difference in the air was made near the surface of the spray as a tracer by heating a SUS wire with large current and the movement of air induced by the spray can be visualized through this density difference. The effects of nozzle hole, injection velocity and ambient air density on the air-entrainment behavior were investigated by this method. The air-entrainment relating to air-fuel ratio and the time dependent change of local air-entrainment were shown. These results indicated that using smaller nozzle hole and increasing ambient air density can increase the air-entrainment into the spray but increasing the injection velocity has little effect on the air-entrainment. Meanwhile, the results of this study were compared with the existing momentum theory, and the possibility of using momentum theory to predict the air-entrainment was described in the paper. Based on comparing the averaged air-fuel ratio inside the spray with both values of measurement and predicted by momentum theory, some discussions were added to help considering the complex phenomena of air-entrainment into a unsteady diesel spray.