The combustion instabilities of supersonic combustion were investigated experimentally in a laboratory-scale scramjet combustor with a cavity flame holder. Ethylene was injected transversely from an orifice to the supersonic flow of Mach 2 with a stagnation temperature of 1900 K and a total pressure of 0.37 MPa. The dynamic pressure, CH* chemiluminescence and shadowgraph images were measured with a pressure sensor and a high-speed video camera. Dynamic pressure was analyzed by fast Fourier transform, and time-resolved CH* chemiluminescence images were modally decomposed by the sparsity-promoting dynamic mode decomposition (SP-DMD). The results indicated that two combustion instabilities were observed for cavity shear-layer stabilized combustion and the oscillation between jet-wake stabilized and cavity shear-layer ram combustions for the power spectral density (PSD) of pressure. In the case of the combustion instability of cavity shear-layer stabilized combustion, a dominant peak of approximately 128 Hz was observed for the PSD of pressure. This instability corresponded to an entire flame oscillation of the cavity shear-layer stabilized combustion, which was validated by the SP-DMD and a low rank reproduction with 10 modes. This was driven by a fuel injection oscillation in the injection orifice. In the case of oscillation between the jet-wake stabilized and the cavity shear-layer ram combustions, peaks around 1600 Hz were observed for the PSD of pressure. This mechanism was also explained by the SP-DMD modes and a low rank reproduction using within 10 modes. The DMD and shadowgraph images indicated that the vortex formed by a separation of the boundary layer induced a strong jet-wake flame, resulting in the temporal thermal choke followed by cavity shear-layer stabilized ram combustion. The data-driven approach with SP-DMD clarified the combustion instability mechanisms of the supersonic combustion in detail.

在带有腔火焰支架的实验室规模超燃冲压燃烧器中，通过实验研究了超音速燃烧的燃烧不稳定性。将乙烯从孔口横向注入马赫数2的超声速流中，停滞温度为1900 K，总压力为0.37 MPa。用压力传感器和高速摄像机测量动态压力，CH *化学发光和阴影图图像。通过快速傅里叶变换分析动态压力，并通过稀疏促进动态模式分解（SP-DMD）对时间分辨的CH *化学发光图像进行模态分解。结果表明，对于腔室剪切层稳定燃烧，观察到两种燃烧不稳定性；对于压力的功率谱密度（PSD），喷射尾流稳定与腔室剪切层夯燃烧之间存在振荡。在腔剪切层稳定燃烧的燃烧不稳定性的情况下，对于压力的PSD观察到大约128Hz的主峰。这种不稳定性对应于腔体剪切层稳定燃烧的整个火焰振荡，这通过SP-DMD和10种模式的低阶再现进行了验证。这是由喷射孔中的燃料喷射振荡驱动的。在稳定的喷气尾流和型腔剪切层冲压燃烧之间发生振荡的情况下，在PSD的压力处观察到了1600 Hz附近的峰值。SP-DMD模式和在10种模式内使用的低秩再现也解释了这种机制。DMD和阴影图图像表明，由边界层分离而形成的涡流产生了强烈的喷流尾焰，导致暂时的热thermal流，随后是腔剪切层稳定的冲压燃烧。SP-DMD的数据驱动方法详细阐明了超音速燃烧的燃烧不稳定性机理。