马赫数10条件下冲压发动机内氢气燃烧特性试验

Hydrogen combustion experiments of a fullpath scramjet at a Mach 10 condition of high enthalpy shock tunnel

针对高马赫数超燃冲压发动机面临的高效燃烧组织挑战,本文提出了一种凹腔后缘激波强化的高马赫数超声速燃烧组织技术,并设计了一套燃烧室采用双侧对称布置凹腔结构的三维发动机试验模型。采用OH*基化学发光光谱诊断与壁面测压相结合的试验手段,在自由活塞驱动激波风洞的名义Ma=10流场中,对凹腔上游横向氢气射流的燃烧特性进行了研究,并讨论了模拟流场的重复性,给出了氢气燃烧演化特征、火焰稳定结构及释热特性。不同车次的总压等流场参数表明试验流场具有较高的重复性,可保障氢气燃烧特性的可复现性。通过观察试验过程中OH*基动态发光特征发现,在高焓激波风洞发动机试验中采用燃料提前喷注的方法使发动机流道在空气主流到来之前充盈大量的氢气,进而在主流到达发动机内的瞬间形成所谓“激波管流动-燃烧”效应,使来流空气与氢气接触面发生自点火与剧烈燃烧,产生显著不同于发动机正常工作情况下的点火与燃烧机制,但随着主流趋于平稳,“激波管流动-燃烧”效应消失,在高总温气流的自点火效应与凹腔后缘的X型激波耦合作用下,火焰稳定在凹腔上游近壁面区的氢气射流尾迹区和凹腔后缘附近的全流场中。通过分析壁面压力分布特征发现,凹腔后缘的X型激波实现了燃烧的强化与火焰的稳定,并获得了最显著的释热压升。这些结果表明高马赫数冲压发动机可利用凹腔后缘X型激波强化燃烧和稳定火焰。

To explore how to improve the performance of scramjet engines operating at a flight Mach number around 10,we proposed a method to achieve combustion enhancement by means of the cavity-aft-shock,and designed the three-dimensional scramjet article with a both-side-symmetrically-configured cavity combustion chamber.Using a combination of the excited OH*chemiluminescence visualization and wall pressure measurement,burning characteristics of the hydrogen jet injected upstream of the cavity in a highly supersonic crossflow of the scramjet combustor were experimentally studied at the nominal condition of Ma=10 in a free-piston driven high enthalpy shock tunnel.The repeatability of the simulated flow field was discussed,and the evolution characteristics of hydrogen combustion,flame-stabilization structure,and heat release profiles were given.Across all experimental cases,the stagnation parameters of the freestream flow remained constant with low standard deviation,allowing for effective analysis of hydrogen combustion characteristics.The evolving features of OH*chemiluminescence indicate that the so-called"shock tube flow-combustion"in the engine article is formed at the initial stage of the crossflow establishment due to the employment of the fuel injection before the arrival of the highly supersonic crossflow,leading to the autoignition at the contact interface of the high temperature crossflow with the injected hydrogen,while the flame ultimately anchors at the jet wake of the bodyside wall and the whole flow path around the cavity aft due to the coupling interaction of the autoignition in high total temperature crossflow and cavity-aft X-type shock pattern.The OH*luminosity and wall pressure distribution features within the effective test time demonstrate that the combustion enhancement is associated with the cavity-aft X-type shock patterns,which generate the drastic heat release-induced pressure rise.The results are useful to promote combustion efficiency of high Mach number scramjet engines by means of cavity configuration presented in this paper.