柴油与生物柴油不同长径比喷嘴内空穴流动的试验

Visualization Experiment on Cavitating Flow of Different LengthDiameter Ratios Using Diesel and Biodiesel in Diesel Engine Nozzles

在柴油机透明喷嘴内部空穴流动可视化试验台上,基于高速数码摄影和长工作距离显微成像技术,研究了不同长径比结构的透明喷嘴内柴油和生物柴油的空穴流动特性及其对喷雾的影响,分析了空化初生和水力柱塞流出现的临界点及水力柱塞流出现过程中的流动能量损失问题.研究表明:柴油和生物柴油的空穴流动形态相似,但生物柴油比柴油难发生空化,单相流阶段,柴油的流量系数高于生物柴油,空穴发展到一定阶段,生物柴油的流量系数开始高于柴油.喷孔长度越长,空化和水力柱塞流现象越难出现,在长径比结构为8的喷嘴中没有出现水力柱塞流现象.且水力柱塞流出现的瞬间,柴油的流量系数下降程度比生物柴油大,即能量损失大.

The complicated cavitating flow inside small-scaled diesel nozzles has attracted more investigation,and cavitating flow characteristics of biodiesel in nozzle with different structures is instructive to the high efficient use of biodiesel in diesel engine. Based on the cavitating flow visualization experiment with a transparent scaled-up injector nozzle tip,a high-speed digital camera and a long working distance microscope,the cavitating flow in transparent nozzles with different length-diameter ratios using diesel and biodiesel was studied in this paper. Meanwhile,the energy loss in the occurrence of hydraulic flip was also studied. Test results showed that diesel was easier to develop into the cavitation,and longer length to diameter of orifice can inhibit the occurrence of cavitation and hydraulic flip. Discharge coefficient of diesel is larger than that of biodiesel in the single-phase flow region,while it is much smaller than that of biodiesel in the cavitating flow and the hydraulic flip regions. Hydraulic flip phenomenon appeares in the nozzles with length-diameter ratios of 4 and 6,but does not occur for the length-diameter ratio of 8.