双模态超燃冲压发动机点火方案对比试验

Experimental Comparison on the Scheme of Ignition in Dual-Mode Scramjet

关键词:  燃烧室  双模态超燃冲压发动机  点火  火焰传播  压力响应  凹腔驻留火焰 

Key words:  Combustor  Dual-mode scramjet  Ignition  Flame propagation  Pressure response  Cavity trapped flame

摘要:

在来流马赫数2、总温840K的双模态超燃冲压发动机扩张型燃烧室的冷启动工况下,对凹腔上游的煤油横向射流喷雾的三种点火方案(热射流点火、乙烯引导点火、凹腔内局部补氧点火)进行了试验对比研究。采用高速相机拍摄了不同点火方式下的初始火焰生成和发展过程,对比分析了各种点火方案的点火接力过程和压力响应特点。试验研究表明,热射流火焰和喷雾下游掺混燃烧后通过火焰逆传形成凹腔驻留火焰,室压受热射流供应及其与喷雾作用的非定常特性的影响较大；乙烯引导点火受乙烯燃烧强度的影响,在研究的参数范围内,由于生成的乙烯火焰较弱,易被煤油喷雾浇熄,旨在凹腔内形成接力火焰的点火方法未能实现乙烯引导的成功点火；在凹腔内局部补氧能够改善煤油喷雾的点火性能,点火接力过程过渡平稳。 

Abstract:

Three kinds of ignition scheme of kerosene spray were investigated experimentally in an expanding scramjet combustor with incoming air total temperature of 800K and speed of Mach 2which related to a typical cold start-up condition of dual-model scramjet. The fuel was injected vertically into the crossflow upstream the flame-holding cavity. The flame propagation and the characteristic of pressure response during the process of ignition were observed and compared with high speed camera and pressure sensor. Results reveal that ignition of hot gas injection is characterized by the far-field diffusive burning between spray and injected hot gas. The trapped flame within cavity is created due to the flame propagation upstream. Interaction between hot gas jet and spray has a great influence on the combustor pressure response as well as the dynamic injection of hot gas. The ignition result of pilot C₂H_4flame is affected by the intense of C₂H_4flame. C₂H_4flame is too weak to ignite the spray flame which is extinguished by cold spray and cavity trapped flame can not be established. Oxygen addition within cavity can improve the performance of spray ignition with a smooth pressure response during the process of flame relay. 