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为探讨柴油机燃烧的机理,在宏观地研究燃烧状态和排气特性的同时,有必要对燃油喷雾液滴的蒸发、着火,以及燃烧等微观运动进行观察。但是几乎没有见过在实机的高温高压作用下,直接观察正在蒸发或燃烧着的燃油液滴的先例。本研究系使用带涡流室的空冷二冲程柴油机。从整体照片宏观地观察燃烧室内的喷雾,并直接对涡流室中任意时间和位置上的液滴群做直接的瞬时摄影。由这些照片观察喷雾的整体运动,以及蒸发、燃烧等过程中液滴平均直径随时间的变化,和液滴飞行状态。进而研究了平均粒径与碳黑生成量的对应关系。其结果说明了以下事实。对比二、三个不同的涡流室所得的喷雾整体照片可以看出涡流的影响,涡流促进燃烧的情况及对燃烧状态造成的差别。由放大的液滴照片,确认在液滴后面有发暗的尾部,虽还不能确定这是燃油蒸气还是火焰,但由此可知液滴各自的飞行方向。燃油喷射量越多,在涡流室内不同位置、不同时间蒸发燃烧中的液滴平均粒径就越小,着火也越早。平均粒径与喷油压力和涡流室压力差的大小有关,压差增大,则平均粒径减小。同时,由涡流室中心沿半径方向的液滴平均粒径分布,可知平均粒径几乎相同的液滴,分布情况也相同。就液滴平均直径对碳黑生成量的影响来说,燃油喷射量越多,平均直径越小,排气中的碳黑生成量也越大。
In order to explore the mechanism of diesel engine combustion, it is necessary to observe the microscopic motion of fuel spray droplets such as evaporation, ignition and combustion while studying the combustion state and exhaust characteristics macroscopically. However, there have been few precedents that directly observe the droplets of fuel that are vaporizing or burning under the action of high temperature and high pressure from real machines. This study used an air-cooled two-stroke diesel engine with swirl chamber. Observe the spray in the combustion chamber macroscopically from the overall photo and make direct momentary photography of the drop group at any time and position in the vortex chamber directly. From these photographs, we can observe the whole movement of the spray, the change of the average diameter of the droplets with the passage of time during evaporation, combustion and the like, and the state of droplet flight. The relationship between the average particle size and the amount of carbon black was also studied. The results illustrate the following facts. In contrast to the two or three different swirl chambers, the overall picture of the spray obtained shows the effects of eddy currents, the presence of eddy currents to promote combustion, and the differences in combustion conditions. From the magnified droplet photograph, it is confirmed that there is a dusky tail behind the droplet. Although it is not yet known whether this is a vapor or a flame, the respective droplet directions are known. The greater the amount of fuel injection, the vortex chamber at different locations, different times, the smaller the average diameter of droplets in the evaporative combustion, the fire is also earlier. The average particle size is related to the pressure difference between injection pressure and vortex chamber. When the pressure drop increases, the average particle size decreases. At the same time, the average particle size distribution of the droplets in the radial direction from the center of the vortex chamber shows that the droplets having the same average particle diameter have the same distribution. In terms of the influence of the average diameter of droplets on the amount of carbon black produced, the larger the amount of fuel injection, the smaller the average diameter, the larger the amount of carbon black generated in the exhaust gas.