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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。
In the flow Mach 1.8, the total temperature of 800K supersonic combustion in-line test bed carried out ethylene / air plasma jet ignition pilot study. The plasma jet flow field structure, self-luminous flame image and flame pattern were photographed by using a high-speed camera. The effects of fuel injection pressure, mixed fuel and plasma jet medium on the ignition characteristics were analyzed. The experimental results show that the shearing action between the plasma jet and the main stream forms a large-scale vortex structure, and the jet wake is mainly located near the cavity shear layer. The global characteristics of the jet and the mainstream are mainly manifested by jet-induced On the bow shock, the jet momentum increases and the shock intensity increases. The fuel injection pressure increased, the steady-state pressure of the combustion chamber increased after ignition, and the pressure response curve advanced earlier. When the ethylene injection pressure was lower than 0.33MPa, the pressure curve showed a certain oscillation and the combustion chamber could not establish a stable flame. At 0.33-0.624 MPa, there is a transition from super-combustion to sub-combustion in the combustion process, and the ignition process tends to be stable above 0.624MPa. The ignition lean limit of ethylene and methane blends appears near the injection pressure of 0.394 MPa. Although the plasma jet can provide high temperature working fluid, part of the gas molecules mixed with cold air in the jet wake will dilute the fuel concentration and further affect the ignition performance.