Experimental study on the injection characteristics of dimethyl ether–biodiesel blends in a common-rail injection system

Abstract

The injection rate and dynamic behaviour during and after the injection of dimethyl ether–biodiesel blends in a common-rail injection system are experimentally studied. The characteristics of the instantaneous line pressure evolution induced by the injection are obtained. In comparison with the injection of biodiesel, the injection of 100 wt % dimethyl ether starts later, but the starts of injection of other fuels are almost at the same time. Increasing the dimethyl ether blending ratio leads to a retarded end of injection and a significantly prolonged injection duration, but the peak injection rate changes little. With increasing rail pressure, the early rate of change in the injection rate with time and the peak injection rate increase, and the injection rate fluctuates more strongly. With increasing energizing time, the start of injection and the peak injection rate remain unchanged. The curves of the line pressure fluctuations at the injector inlet are similar for all dimethyl ether–biodiesel blends. When the dimethyl ether blending ratio is increased from 30 wt % to 100 wt %, the drop in the amplitude of the line pressure at the start of injection becomes smaller, the peak pressure decreases gradually and the phase is retarded. The duration of the line pressure fluctuations after injection becomes longer with increasing dimethyl ether blending ratio. By increasing the rail pressure, the line pressure at the start of injection drops more quickly, with a larger amplitude. At the end of injection, the magnitude of the peak pressure increases with an advanced phase, and the duration of the pressure fluctuations increases. By increasing the energizing time, the line pressure drop at the start of injection is unchanged, and the first line pressure peak increases with a retarded phase.