The dynamics of an optical axisymmetric scramjet, preferred for generic combustion and flameholding studies without the corner boundary-layer effects that distort the freestream and flame propagation in rectangular scramjets, is investigated at Mach 4.5. Ethylene fuel is injected into supersonic flow via sixteen sonic fuel nozzles equally spaced in a circumferential direction and inclined at 45° to the freestream. The gaseous fuel is auto-ignited by high-enthalpy flows that are compressed and decelerated by shockwaves and boundary layers while passing through the scramjet inlet and isolator. An axisymmetric cavity located downstream of fuel injectors achieves flame holding by providing slow flow recirculation regions and inducing shockwaves at cavity leading edge and ramp to redirect and recompress flows. Flow and flame behaviors are characterized by high speed flame chemiluminescence imaging and static pressure measurement, while the detailed flame structures are resolved by instantaneous ground-state hydroxyl radical (OH) distributions using planar laser-induced fluorescence (PLIF). Numerical simulation is employed to aid the inlet/isolator design to avoid unexpected unstart introduced by shock-boundary layer interactions in the shock train region. The Mach number profiles in the radial direction are measured using a Pitot probe at the combustor exit. We demonstrate supersonic flameholding with the presence of a cavity at ethylene fueled conditions where stable combustion is achieved without scramjet unstart under both mass and heat loading. The heat addition from the cavity-stabilized flame mainly reduces the flow Mach number in the near-wall flow region. In the core flow region, the flow Mach number is decreased by the jet- and cavity-induced shockwaves and minimally affected by heat addition.

在4.5马赫下研究了光学轴对称超燃冲压发动机的动力学，该动力学优选用于一般燃烧和火焰保持研究，而没有使矩形超燃冲压发动机中的自由流和火焰传播变形的角边界层效应。乙烯燃料通过沿周向均匀分布且相对于自由流倾斜45°的16个声波燃料喷嘴注入超音速流。气体燃料通过高焓流自动点燃，该高焓流在通过超燃冲压发动机入口和隔离器时被冲击波和边界层压缩和减速。位于燃油喷射器下游的轴对称腔体通过提供缓慢的流动再循环区域并在腔体前缘和斜面处引发冲击波来重定向和重新压缩流，从而实现了火焰保持。流动和火焰行为的特征在于高速火焰化学发光成像和静态使用平面激光诱导的荧光（PLIF）通过瞬时基态羟基自由基（OH）分布解析详细的火焰结构。采用数值模拟来辅助进气口/隔离器的设计，以避免在冲击波列区域中由于冲击边界层相互作用而引起的意外启动。使用燃烧器出口处的皮托管探针测量径向的马赫数分布。我们证明了在以乙烯为燃料的条件下存在腔的情况下的超音速火焰保持，该燃烧可实现稳定的燃烧，而无论是在质量负荷还是在热负荷下均不会使超燃冲压发动机启动。来自腔稳定火焰的热量添加主要减少了近壁流动区域中的流动马赫数。在核心流动区域，