两种优化组合式燃料喷注方案的凹腔稳焰特性实验研究

Experiments on flame stabilization of two combined fuel injection schemes in a cavity⁃based combustor

在马赫数2.0,总压0.98 MPa和总温920 K的超声速来流条件下,针对现有常见的凹腔组合式燃料喷注方案出现的燃烧不稳定和火焰吹熄现象,通过改变凹腔上游壁面双路燃料喷注的位置,设计了两种优化的凹腔组合式喷注方案,并对不同燃料喷注方案下的火焰稳定过程进行研究。通过高速摄影和CH*基自发辐射成像技术,详细观测了后缘突扩凹腔燃烧室中乙烯火焰传播过程。研究表明,原始的喷注方案容易发生火焰振荡,并伴随着火焰回传现象以燃烧模式的转换;当量比超过0.3时,就难以实现稳定燃烧,并出现火焰吹熄现象。两种改进的喷注方案均能增强燃料射流与凹腔的相互作用,可在更宽燃料喷注当量比范围内维持火焰不被吹熄。相比于增加上游喷注与凹腔前缘距离的喷注方案而言,增加双路燃料喷注之间距离的喷注方案的稳焰效果更好,燃烧反应区也更加靠近凹腔前缘,燃烧释热也更强。这种喷注方案可为超燃冲压发动机燃烧室中凹腔燃料喷注方案的优化设计提供参考。

Experimental investigation on the flame stabilization based on cavity combined injection schemes was conducted in a Ma = 2.0 supersonic inflow with total pressure of 0.98 MPa and total temperature of 920 K.In order to suppress the combustion instability and flame blowout of the existing combined cavity injection scheme,two optimized combined cavity injection schemes were designed by changing the injection positions of double injection on the upstream wall of the cavity.High speed photography and CH*radical spontaneous emission technologies were used to observe the flame propagation process in an ethylene fueled model scramjet combustor with a rear-wall-expansion cavity.The results show that the original flame oscillation is easy to occur in the initial injection scheme,accompanied by the flame flashback and the transition between different combustion modes. When the equivalence ratio is more than 0.3,it is difficult to achieve stable combustion and phenomenon of flame blowing out occurs.Both of the two improved injection schemes can enhance the interaction between the fuel jet and the cavity,and keep the flame from blowing out in a wider range of fuel equivalence ratio.Compared with the injection scheme with increasing distance between the upstream injection and the cavity leading edge,the injection scheme with increasing distance between the two fuel injections has a better flame stabilization with combustion reaction zone closer to the front edge of the cavity and also more intense heat release.This injection scheme can provide reference for the optimization design of fuel injection scheme in the cavity of scramjet combustion.