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

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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.