THE IGNITION BEHAVIOR OF HIGH-TEMPERATURE AIR-SPRAY SYSTEMS AS A COMPLEX SYSTEM

喷雾的点火行为对高温空气的流动场和温度场非常敏感，它们对点火延迟有很大的影响。这一事实似乎意味着高温空气喷射系统显示出对初始条件高度敏感的复杂性。因此，1998年，通过垂直向高温气流中注入液体燃料，研究了速度、湍流度和温度对点火行为和延迟的影响。此外，还研究了喷雾对迎面壁面的冲击对点火延迟的影响。结果表明，在防止喷雾撞击壁面的情况下，点火行为发生了显著变化。1999年，利用高速摄像机对点火过程进行了详细的研究。结果表明，在高温条件下，点火发生在喷嘴附近，而在低温条件下，点火发生在撞击壁面后。当与壁面碰撞后发生点火时，它始于喷管的上游。此外，如果将OH自由基化学发光测定的点火延迟与发光火焰出现时间进行比较，前者仅为后者的一半或更少。这说明点火延迟数据受点火判据的影响较大；火焰：蓝色火焰（小火焰）或发光火焰的外观综上所述，由于点火发生在喷嘴周围共流的低速区，因此高温气流的速度和湍流对点火有很强的影响，喷嘴对迎面壁面的撞击显著地改变了点火的过程和延迟，点火判据对点火延迟数据有很强的影响。

The ignition behavior of a spray is highly sensitive to the flow and temperature fields of high-temperature air, and they considerably alter the ignition delay. This fact seems to imply that a high-temperature air-spray system shows complexity that is highly sensitive to the initial condition. In 1998, therefore, the effects on the ignition behavior and delay of the velocity, turbulence and temperature of a high-temperature air stream were studied by perpendicularly injecting a liquid fuel into the stream. The effects of spray impingement against the confronting wall on the ignition delay were also examined. It was found that the ignition behavior markedly varied if the spray was prevented from impinging against the wall. In 1999, the detailed ignition processes were studied using a high-speed video camera. It was found that, in a high-temperature condition, ignition initiated near the injection nozzle, and that, in a low-temperature condition, ignition took place after impinging against the wall. When ignition took place after impingement against the wall, it initiated in the upstream of the injection nozzle. If, in addition, the ignition delay determined from the OH radical chemiluminescence was compared with the time of luminous flame appearance, the former was only a half or less than the latter. This fact implies that ignition delay data are significantly affected by the criterion of ignition ; either the appearance of a blue flame (a flamelet) or that of a luminous flame. It was found, in summary, that ignition was strongly affected by the velocity and turbulence of the high-temperature air stream since it took place in the co-flowing low-velocity region around the spray, that the impingement of the spray tip against the confronting wall significantly altered the process and delay of ignition, and that the criterion of ignition strongly affected the ignition delay data.