Experimental study on dynamic injection behaviors of biodiesel and its blends in a common-rail injection system

Abstract

The dynamic injection behaviors of pure biodiesel, high-proportioned biodiesel blends, and low-proportioned biodiesel blends in a common-rail injection system are researched. The effects of biodiesel ratio in the blended fuel and injection condition on the injection rate, cycle injection quantity, and fuel line pressure at the injector inlet are determined. The findings show that the injection duration is extended with the decrease in biodiesel ratio in the blended fuel, and fluctuation amplitude of injection rate in the stable injection stage increases. The first four pressure peaks for pure biodiesel decrease rapidly, while for blends, they decrease slowly, which results in an increasing difference of four pressure peaks between pure biodiesel and blends. With the decrease in biodiesel ratio, the mean volume injection quantity for three fuels gradually increases in the same injection condition. The coefficient of variation of the cycle injection quantity value for biodiesel and its blends with 30 cycles increases. The coefficient of variation value for biodiesel is between 0.4% and 0.7%. Compared with pure biodiesel, the mean volume injection quantity for BD70 increases by about 20–32%, and the coefficient of variation value is between 0.7% and 1.7% for high-proportioned biodiesel blends. The mean volume injection quantity increases by about 36–43% for low-proportioned biodiesel blends and the coefficient of variation value is between 1.1% and 2.1%.