Development of a Very High Pressure Injection System for Diesel Engines

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To reduce particulates and oxides of nitrogen emitted from diesel engines, much efforts are being made to realize the high pressure injection systems. This is because injection at pressures much higher than those of ordinary diesel engines effectively promotes mixing of the injected fuel and the surrounding air, thereby reducing the heterogeneity which greatly affects the formation of soot and carbonaceous matter. However, it is usual that one confronts difficulties, such as fuel leakage and abnormal injections, when an ordinary injection system is converted to a high-pressure system. Similar difficulties are associated even at novel injection systems such as unit injectors and ones that use a booster piston.In the present study, a new injection system is proposed to remove these difficulties in attaining high-pressure injection. Basically, this system uses the hydraulic ram in boosting pressure, relying on a tapered convergent pipe that has a larger inlet cross-sectional area and a sm … More aller outlet cross-sectional area. A low fluid-dynamic impedance at the inlet affords to strongly accelerate a free-piston hammer by which a plunger is driven, and this leads to a very high hydraulic pressure at the other end of a higher impedance. The first part of this study deals with how the convergent tube boosts the hydraulic pressure at the outlet where the injection nozzle is installed. The analysis is based on the method of characteristics for one-dimensional wave propagation. The results show that the ram effect can successfully be used as a pressure booster in the injection system. Next, the high-pressure injection system that uses a convergent tube is studied based on computer simulation taking into account every dynamic effect, for two types of free-piston hammer pumps operated semi- and full-hydraulically. Both pumps are featured by an electro-magnetic control to initiate the motion of the hammer, to enable precise control of injection timing. The results well suggest a capability of attaining a very high pressure injection and also exhibit many advantages compared to conventional injection systems. Less