摘要:
To research the nozzle cavitation and near-field spraying characteristics,visualization experiments were carried out using a high-speed camera and a single transparent up-sized nozzle to observe the nozzle cavitation and near-field spraying behavior of three ethanol-diesel blended fuels with the volume fractions of ethanol of 0%,5%,10%.The normalized cavitation length,discharge coefficient,cavitation number,Reynolds number and near-field spraying cone angle were analyzed under the injection pressures of 0.16-0.36 MPa.The three ethanol-diesel blended fuels were named E0D100N0,E5D90N5 and E10D85N5 respectively,wherein the letters of E,D and N represent ethanol,diesel and n-butanol respectively while the subscripts indicate the volume fraction of each component.The experimental results showed that,with the increase of volume fraction of ethanol,the threshold injection pressures corresponding to original cavitation and super cavitation were decreased,and the periods of developing cavitation were shortened but the periods of supercavitation were extended.During the no-cavitation stage,the change of volume fraction of ethanol had no obvious influence on near-field spraying cone angle;during the developing cavitation stage,the near-field spraying cone angle increased with the increase of volume fraction of ethanol;and during the hydraulic flip stage,the near-field spraying cone angles of three blended fuels were all close to zero.Under the same injection pressure,the discharge coefficients and the Reynolds numbers of E0D100N0,E5D90N5 and E10D85N5 increased in sequence,and when hydraulic flip appeared inside the nozzle,the discharge coefficients and the Reynolds numbers of these three blended fuels were all decreased sharply.%为了完善乙醇-柴油混合燃料的喷嘴孔内空化现象及近场喷雾特性研究,利用高速摄像机和放大尺寸单孔透明喷嘴观察乙醇体积分数分别为0%、5%和10%的3种乙醇-柴油混合燃料在喷孔中的两相流动及近场喷雾,在喷射压力为0.26~0.46 MPa的范围内对空化特征长度、流量系数、空化数、雷诺数等特性参数及喷嘴近场喷雾特性进行了分析.将3种混合燃料分别命名为E0 D100 N0、E5D90 N5和E10 D85 N5,其中E、D、N分别代表燃料中的乙醇、柴油和助溶剂正丁醇,下标表示各成分的体积分数.试验结果表明:随着燃料中乙醇含量的增加,E0 D100 N0、E5 D90 N5和E10 D85 N5的空化初生及超空化对应的阈值喷射压力依次降低,空化发展期逐渐缩短,超空化期相应延长;在无空化和空化初生期乙醇含量的改变对近场喷雾锥角的影响并不明显,在空化发展期和超空化期,3种燃料近场喷雾锥角随乙醇含量的提高而增大,在柱塞流阶段,3种燃料近场喷雾锥角均接近0°;在同等喷射压力下,E0 D100 N0、E5 D90 N5和E10 D85 N5对应的流量系数和雷诺数依次增大,在柱塞流阶段,3种燃料对应的流量系数和雷诺数均急剧下降.