Experimental investigation on influence of inlet/outlet pressures on submerged jet flow in common rail injector

Abstract

The fuel flow in the working chamber of the common rail fuel injector, which is a submerged jet flow, determines the needle movement and causes great effects on the fuel injection performance. This work presents an experimental investigation on the submerged jet flow characteristics of a cylindrical orifice under conditions of varied boundary pressures. A full-scale optical test rig is set up to examine the submerged flow of the cylindrical orifice based on a fuel pump test bench. The optical experimental results reveal that the inner cylindrical orifice flow induces cavitation and causes influences on the submerged jet flow. As the inner cavitation is at the cylindrical orifice outlet, the cylindrical orifice discharge coefficient declines but the mass flow rate becomes choking. The test results also show the boundary pressures (the inlet and outlet pressures) of the cylindrical orifice have great influences on the impingement force of the submerged jet flow. The development process of the impingement force is divided into two periods: the stable period and the fluctuation period. Moreover, the impingement force increases quadratically with the increase in the mass flow rate. Once the choking flow happens, it is useless to increase the jet impingement force by improving the inlet pressure.