2024 Volume 67 Issue 2 Pages 43-51
The forced ignition instability and combustion instability in a scramjet engine were investigated experimentally and numerically using modal analysis. In this study, proper orthogonal decomposition (POD) was applied to OH* chemiluminescence image data obtained during previous supersonic combustion experiments. In this scramjet combustor, a micro-rocket torch was installed in the cavity. First, to clarify the combustion instability phenomenon in the cavity and flow paths, a POD analysis was performed using the OH* chemiluminescence image data. The maximum power spectrum density peak shifted to the high-frequency region in high-order modes. The combustion oscillations between 100 and 500 Hz were attributed to injector flame feedback from the fuel or torch jet gas because the fuel and torch gas were directly injected into the shear layer, where fuel combustion occurred. Next, to clarify the forced ignition instability phenomenon in the cavity, the POD modes near the torch jet orifice were investigated. The low frequencies near the torch jet orifice within the cavity were likely associated with the torch gas injector flame feedback because the frequency spectra of the inner pressure oscillations in the micro-rocket torch matched the frequency spectra peak near the torch jet orifice in the cavity.
