|Budget Amount *help
¥3,500,000 (Direct Cost : ¥3,500,000)
Fiscal Year 1999 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1998 : ¥2,300,000 (Direct Cost : ¥2,300,000)
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 again
st 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.
本年度は,観測窓を通して着火過程を高速度ビデオカメラで撮影し,着火の状況を詳細に検討した.高温条件では噴口付近で着火が生じるのに対して,低温条件では衝突板に衝突した後に着火が生じ,中間の条件では噴口付近と衝突板近傍の2点で着火の生じることが判明した.また,衝突板に衝突した後に着火が起こる場合には,噴射弁より上流で着火が生じている.さらに,OHラジカルの化学発光を使って検出される着火遅れを輝炎の出現時間と比較したところ,前者は後者の半分近くに過ぎなかった.したがって,青炎 (フレームレット) の発生をもって着火とするか,輝炎の発生をもって着火とするかで,着火遅れの値は相当の影響を受けることが判明した.以上を総合すると,着火は噴霧副流部の低流速域で生じるため,高温空気の流速と乱れの影響を強く受けること,対向壁への噴霧先端の衝突は着火過程と着火遅れを著しく変化させること,着火の検出方法は着火遅れのデータに大きな影響を与えること,等が判明した. Less