LPG/柴油混合燃料喷雾的研究

【作者】 武涛；

【导师】 曹建明；

【作者基本信息】 长安大学 ， 载运工具运用工程， 2004， 硕士

【摘要】 燃油的雾化质量对发动机的动力性、经济性和排放性有着重要的影响。为了探讨LPG／柴油混合燃料喷射的雾化效果，本文首次采用高分辨率数码照相机试验研究了柴油和LPG／柴油混合燃料的喷雾特性，包括喷雾锥角、贯穿距离、液滴尺寸分布、平均直径、特征直径和发散度和对雾化效果的影响；并比较了纯柴油和不同混合比例的LPG／柴油混合燃料的雾化特性，结果表明：柴油中掺混一定量的LPG有利于改善雾化。随着掺混比的增大，由于溶气喷射的闪急沸腾效应，雾化效果改善明显，LPG／柴油混合燃料喷雾的SMD比纯柴油的减小6％～11％。高分辨率数码照相方法方便、可靠、高效，用于喷雾质量的比较研究，可以推广应用。运用最大熵原理、质量守恒和动能守恒定律建立了喷雾液滴尺寸／速度联合分布函数，液滴速度分布函数和液滴尺寸分布函数数学模型，结果表明：速度分布曲线显示低速和高速液滴的数目均较少，中间速度的液滴数目较多，当液滴尺寸较小时，液滴速度数目分布曲线平缓，且高速液滴的数目相对较多，说明小直径液滴速度范围较广；喷射速度越大，小直径液滴相对越多，雾化质量越好；纯柴油和L30的速度分布曲线非常接近，说明纯柴油和L30的速度分布差别不大，L30速度分布图的峰值比柴油略小，且略向大速度方向偏移，说明L30燃料喷射时，相对于纯柴油喷射，较大速度液滴的数目略有增加。L30尺寸分布曲线峰值相对于柴油向小颗粒方向偏移，而且L30尺寸分布曲线峰值要高于柴油的峰值，说明L30喷雾所产生的小颗粒液滴比纯柴油喷射产生的要多。研究了蒸发和碰撞对液滴尺寸分布的影响，蒸发和碰撞都会减少液滴数目，液滴尺寸分布曲线向大颗粒方向偏移，而且离喷嘴越远，大颗粒液滴分布数目越多。将理论计算的结果与试验结果进行了对比，结果表明：纯柴油的理论分布曲线与试验曲线拟合很好，但L30曲线的峰值向大颗粒方向偏移较多，这是因为模型未考虑LPG在常稳常压下大量蒸发的缘故。当燃料喷入大气环境中，蒸发作用对纯柴油喷雾液滴尺寸分布的影响不明显，碰撞作用的影响占主导地位；而蒸发作用对L30雾化液滴尺寸分布影响很大，不能忽略。更多还原

【Abstract】 The fuel spray is very important to the power performance, fuel consumption , exhaust emission of diesel .In order to research the spray of LPG/diesel mixed fuel, it is the first time that this work studied the atomization characteristics of LPG/diesel, including spray angle, droplet size distribution, mean diameter, typical diameter, diffusion degree and impenetrate distance by using a high spatial resolution digital camera. At the same time, comparison of these characteristics of diesel and two kinds of LPG/diesel mixed fuel was taken. We can conclude that mixing diesel with some LPG is contribution to fine atomization of diesel and more ratio of LPG more high quality of atomization because of the flash boiling effect of diesel fuel containing dissolved gas. The SMD of LPG/diesel fuel reduced by 6%~11% comparing with that of diesel. The method of high-resolution digital camera is convenient, reliable and efficient .It can be popularized to apply to comparing spray characteristics. This paper has set up the mathematic models of droplet size and velocity joint distribution, droplet velocity distribution and droplet size distribution by utilizing maximum entropy principle and conservation laws of mass and kinetic energy to the spray process. The velocity distribution graphs show the number of low and high speed droplets is small, yet the number of moderate speed droplets is big .The droplet velocity distribution curve of small dimension droplet is flat and wide, and high speed particles are more, which indicates the velocity range of small particles wide. More high injection speed is, more small dimension droplets are produced and spray quality is enhanced. The similarity of velocity distribution curves of diesel and L30 indicates the diesel and L30 distributions have little difference. However the peak of L30 velocity distribution graph is little lower than that of diesel and move for high-speed droplets direction, which illuminates high-speed particles of L30 increased relative to diesel injection. The spray size distribution curve peak of L30 is higher and moves for small particles direction comparing with that of diesel ,which shows that L30 injection produced more small particles than diesel .Studying the effects of evaporation and coalescence on droplet size distribution, we find the effects lead to reduce droplet number and the size distribution curves move for big diameter droplets direction and more distance are away from the nozzle more numbers of big diameter droplets appear. Comparing the results of experiments and prediction, we gain the good accordance of diesel distribution curve between measurement and prediction. Yet the curve peak of L30 moves for big dimension particle direction because of ignorance great evaporation of fuel L30 droplets. When fuel rejects into atmosphere, evaporation has little influence on diesel atomization yet the effect of coalescence is dominant. On the contrary, evaporation effect is dominant in spray of fuel L30.更多还原