Effect of di-n-butyl ether blending with soybean-biodiesel on the near-nozzle spray characteristics

In this work, the near-nozzle spray characteristics of soybean biodiesel, di-n-butyl ether (DBE)/biodiesel blends and 0# diesel were investigated by using a high pressure common-rail injection system and the effect of experiment conditions and fuel physical properties on the near-nozzle spray structures were explored. Microscopic spray images at the near-nozzle field were captured by the high-resolution microscopy. The micro spray cone angle and micro projected spray area were obtained from the processed spray images for quantitative analysis. The results show that the initial spray of diesel is easier to breakup into ligaments and droplets because of smaller surface tension and viscosity compared to that of biodiesel under atmospheric condition. The spray with more ligaments was easily restrained by the ambient gas and promoted to evolve along the radial direction, leading to a wider micro spray cone angle of diesel. The breakup of liquid jet also tends to increase the micro projected spray area of diesel. When 30% of DBE was added into biodiesel, both the micro spray cone angle and projected spray area were increased due to the decreased surface tension and viscosity of the blended fuel. The initial spray images reveal that the high injection pressure favors the spray primary breakup while the high ambient pressure results in worse spray primary breakup. The quantitative analysis shows that the injection pressure has little influence on the micro spray cone angle but results in the increase in micro projected spray area, while both parameters increase significantly under high ambient pressures. (C) 2016 Elsevier Ltd. All rights reserved.