Combustion of Transient Gas Fuel Jet and Process of Entrainment of Ambient Air into Jet

众所周知，柴油机等直喷式发动机的混合气形成过程对缸内燃烧有很大的影响。对雾化气体在射流或喷雾中的卷吸过程进行详细的了解是非常重要的。然而，关于夹带过程的研究很少。柴油机在高温高压下喷射到气缸中的燃油蒸发，并与周围的空气一起携带。因此，为了更好地理解这一现象，由于忽略了蒸发过程，在常压常温的稀薄空气中注入了气体，并研究了卷吸过程。在本研究中，激光片穿过包含射流轴线或垂直于射流轴线的射流横截面。用微粒子和微气球…显示了瞬变射流的瞬时图像和环境空气的运动分别是更多。采用一种利用CCD快门相机的微气球路径线法，近似获得了携带在瞬变气体射流中的气团。在火焰的情况下，火焰是通过在射流启动时点燃氢气射流而形成的，流入射流中的空气与没有燃烧的射流中的Sa相同。然而，单位表面积的空气流入射流的速率较小，并且随着时间的推移而减小。在射流喷射开始后推迟点火时间，由于快速燃烧的湍流扩散，提前形成了可燃混合物，增加了流入射流的空气；也有人说，由于湍流扩散，可燃混合物在撞击壁面时增加。同样的方法也适用于撞击平壁的射流，以研究环境空气对射流的卷吸作用。结果表明，冲击平壁射流的空气质量在冲击一段时间后有所增加，但在喷射期内随着时间的推移几乎没有变化。研究发现，射流尖端附近的卷曲区域是环境空气流入射流的原因。与旋涡大小相对应的致密结构在卷曲区域附近规则地排列。较少

It is well known that the process of mixture formation in direct injection engine such as diesel engine has great influence on the combustion in the cylinder. It is very important to understand the entrainment process of amibient air into the jet or spray in detail. However, few studies have been done on the entrainment process. The fuel injected into the cylinder with high pressure and high temperature in a diesel engine evaporates and goes through with entraining the ambient air. Therefore, for understanding the phenomena easily, a gas was injected for the reason of ignoring the evaporation process and the entrainment process is investigated under the amibient air with atmospheric pressure and room temperature.In this study, a laser sheet was passed through the cross section of the jet that contained the jet axis or was perpendicular to the jet axis. The instantaneous image of the transient jet and the movement of the ambient air were visualized with fine particles and micro-balloons … More , respectively. A path line method for micro-balloons utilizing a CCD shutter camera was applied for obtaining the air mass entrained into a transient gas jet approximately. In the case of the flame, which was formed by igniting the hydrogen jet at the initiation of the jet, the air flowed into the jet was as the same sa in the jet without combustion. However, the rate of air flowed into the jet per unit surface area was smaller and decreased with time. When the timing of the ignition was delayd after the initiation of the jet injection, the combustible mixture was formed in advance and the air flowed into the jet increased because of turbulent diffusion due to the rapid combustion.It is also said that the combustible mixture increases in impinging on a wall because of turbulent diffusion. The same method was applied to the jet impinging on a flat wall in order to inveatigate the entrainment of the ambient air into the jet. As a result, the air mass flowed into the jet impinging on a flat wall increased after the impingement for a while, but was almost the same when the time passed more and more even in the injection period. It was found that the rolled up region near the jet tip casused the ambient air flow into the jet. The compact structures that would correspond to the scale of the vortex were disposed regularly near the rolled up region. Less