Abstract: Ignition of ethylene/air by plasma jet was experimentally investigated on directly connected supersonic combustion facility with air total temperature of 800K and Mach number 1.8. The flow field structure of plasma jet，the self-luminosity flame image and flame schlieren were observed by high speed camera. The effects of fuel injection pressure，mixed fuel and plasma jet medium on ignition characteristics were analyzed. Results reveal that the large scale vortex structure form from the shear impact between the plasma jet and airstream. The wake stream of plasma jet is mainly located near the cavity shear layer. The global feature of jet and airstream is mainly expressed at the bow shock induced by jet. The shock wave is strengthened with the jet momentum increases. The combustor steady pressure after ignition increases and the pressure response curve advances with the increase of the fuel injection pressure. There is pressure oscillation and no steady flame with ethylene injection pressure below 0.33MPa. The combustion mode shifts from supersonic combustion to subsonic combustion with ethylene injection pressure ranging from at 0.33MPa to 0.624MPa. The ignition process tends to be steady as ethylene injection pressure above 0.624MPa. The ignition weak limit of ethylene and methane injection pressure is at the 0.394MPa. Though plasma jet provides high temperature working medium，the gas molecules in the wake stream of plasma jet mixed by cold air play a role on the fuel dilution，in turns，it will affect the ignition performance.

Key words: Supersonic combustor；Plasma jet ignition；Fuel injection pressure；Jet medium；Ignition characteristics

摘要： 在来流马赫数1.8，总温800K的超声速燃烧直连式试验台开展了乙烯/空气等离子射流点火的试验研究。采用高速摄影仪拍摄了等离子体射流流场结构、自发光火焰图像和火焰纹影图，对比分析了燃料喷注压力、混合燃料、等离子体射流介质对点火特性的影响。试验结果表明，等离子体射流与主流之间的剪切作用形成了大尺度的涡结构，射流尾流工质主要存在于凹腔剪切层附近，射流与主流干扰的全局特征主要表现在射流诱导的弓形激波上，射流动量的增加，激波强度增强。燃料喷注压力升高，点火后燃烧室稳态压力升高，同时压力响应曲线提前；乙烯喷注压力低于0.33MPa时，压力曲线出现一定震荡，燃烧室无法建立稳定火焰，在0.33～0.624MPa时燃烧过程存在超燃向亚燃燃烧模态转换，高于0.624MPa时点火过程趋于平稳。乙烯和甲烷混合燃料的点火贫油极限出现在喷注压力0.394MPa附近。等离子体射流虽能提供高温工质，但是其射流尾流中经冷空气掺混的部分气体分子将对燃料浓度起到稀释作用，进而影响点火性能。

关键词: 超声速燃烧室；等离子体射流点火；燃料喷注压力；射流介质；点火特性