Effect of Constant Pressure Delivery Valve on Diesel Injection Characteristics

Abstract

High pressure and short period injection systems have been recently applied to cope with the increasing demands to improve the thermal efficiency and to use heavy fuel oil on medium-speed diesel engines. In such injection systems, however, secondary injection or cavitation in the system tends to occur. Under these conditions, constant pressure delivery valves which have two ball type check valves and a return orifice have been increasingly used in the medium-speed DI diesel engines to work out them.
In this delivery valve system, however, the secondary injection and the risk of cavitation have to be avoided only by the pressure regulating function of the return ball valve and the return orifice. As it was thought that the return orifice is an important factor for avoiding the above problems, it should be optimized in the design.
The authors have experimented the influence of the return orifice diameter on the injection characteristics by using an injection test rig. As a result, the optimum return orifice could be obtained in the range of our present study. Furthermore, the improvement of engine performance was confirmed by using the optimized constant pressure delivery valve.
This paper describes the results of injection characteristics and engine performance at changing the return orifice diameter.