Experimental study on non-vaporizing spray characteristics of biodiesel-blended gasoline fuel in a constant volume chamber

Abstract

Detailed investigation of the spray phenomenology of liquid fuel injection is the primary step to understand better and predict the physical characteristics involved in fuel spray and atomization process. This study focuses on non-vaporizing transient spray characteristics of neat gasoline and biodiesel addition (10%, 20% and 40% by volume) to gasoline in three different ratios under low load and different injection pressure conditions. Different ambient gas densities and injection pressures were tested, which ranged from 10 to 20 kg/m3 and 40 to 120 MPa respectively, with a fuel temperature of 323 K. A z-type shadowgraph was utilized as an optical method to capture the highly transient spray development at 40000 frames per second and a modified image processing algorithm was implemented to determine the spray characteristics. The image processing results revealed that an increase in injection pressure significantly accelerates the spray development process while penetration length increases with the increment of biodiesel fraction. Differences in penetration lengths were much significant under lower injection pressure; however, a further increase in injection pressure diminishes the differences in tip penetration. The spray cone angle was increased for higher gasoline content which promotes a larger spray width and as a consequence, neat gasoline exhibited a larger spray area and volume. However, after a certain period of injection start, spray area and volume of neat gasoline and 10% biodiesel-blended gasoline were surpassed by 20% and 40% biodiesel-blended gasoline. In contrast, a decrease in droplet size was observed according to breakup regimes under high injection pressure and low ambient density. These results imply that the higher biodiesel blending fraction has poor air-fuel mixing capability compared to neat gasoline, and the risk of liquid impingement on the cylinder wall becomes higher if the blended-gasoline contains higher biodiesel percentage.