利用非熱平衡電漿穩駐噴流跳脫火焰

Abstract

本研究為利用非熱平衡電漿穩駐噴流跳脫火焰，主要以實驗方式深入探討非熱平衡電漿對跳脫火焰之穩定性影響。本實驗透過非預混燃燒器產生跳脫火焰，使用三種不同之燃料 (甲烷、丙烷、乙烯) ，透過改變燃料雷諾數與併流空氣流量，觀察電漿對於火焰跳脫高度之影響。可以明顯地看出無論使用何種燃料，在跳脫高度較低的情形時，電漿能夠將火焰 (間歇地) 穩駐於管口上；而跳脫高度較高的情形時，電漿對於跳脫高度之影響較不顯著。在火焰的遲滯現象方面，以甲烷為例，可以看出在電漿放電的情況下，火焰跳脫速度與回駐速度提高了約兩倍。上述兩項結果代表著電漿能夠提升火焰的穩定性。 此外為了更加了解火焰與電漿之間的交互作用，光譜分析能夠確認出火焰及電漿的組成，在本研究中可以明顯地觀察出在電漿放電的情況下，火焰整體的光譜強度有顯著的提升。並使用ICCD觀察火焰與電漿中OH、N2之化學發光，在電漿穩駐火焰於管口的情形時，透過ICCD確實地觀察到該位置OH、N2所產生的化學發光，藉此來確認電漿確實能夠穩駐火焰。本研究初步歸納出了不同燃料的情況下，電漿對於火焰穩定性之影響，以及探討火焰與電漿之間的交互作用。

The present study experimentally investigated the effects of plasma discharges on the stabilization of lifted non-premixed jet flames in a stream of co-flow air. Three different fuels, methane, propane and ethylene, were used. The plasma discharge was produced on the sharp edge of the fuel nozzle exit, facilitating its impact on flame stabilization. It was observed that the application of plasma discharges has an impact on the lift-off velocity, the flame lift-off height and flame hysteresis. The presence of plasma extended the lift-off velocity with an enhancement of approximately 84% when the co-flow velocity was sufficiently low. The flame lift-off height was seen to decrease with the presence of plasma discharge; however, the impact of plasma discharge on lift-off height was gradually diminished as the lift-off height became large. In flame hysteresis studies, both of the flame lift-off and reattachment velocities were increased with the presence of plasma discharge, regardless of the fuel. Results showed that the enhancement on lift-off and reattachment velocities was double with the presence of plasma. Spectroscopic study showed that the emission characteristics, above 400 nm, in downstream of flames were intensified with the presence of plasma discharge, consistent with the flame luminosity visualization. The emission bandwidth broadened when both the plasma and the flame were present. Images obtained from an intensified charge-coupled device (ICCD) camera confirmed the presence of plasma facilitating the flame to anchor at the nozzle exit. The present study investigates the effect of a non-thermal plasma discharge on the stabilization of a lifted non-premixed jet flame.