Study on the influence of fuel injection position on ignition process and combustion characteristics of scramjet with high equivalence ratio

In the scramjet combustor, the turbulent combustion in supersonic inflow is susceptible to various factors, with the fuel injection position being important one of them. As an important intermediate product in hydrocarbon fuels combustion process, CH* is of great significance for combustion process study. This article conducted experiments within a scramjet combustor with a cavity, integrating multispectral temperature measurement and CH* chemiluminescence observation, conducted the following research. Firstly, we investigated the ignition of the two-stage injection scheme. And then, the research investigated the influence of the upstream injection position on combustion characteristics in two-stage injection scheme. The results indicated that the ignition for both injection schemes initiated downstream the cavity. However, variations were observed in the upstream flame propagation. In the two-stage injection scheme, changes in the upstream injection position notably impacted ignition stability. The injection position near the cavity enhanced ignition stability, but it caused more instability in the global flame stage and flameout stage. In addition, based on the results obtained from chemiluminescence and multispectral temperature measurements, the change in upstream injection position in two-stage injection scheme exhibited minimal influence on the temperature field distribution, but significantly impacted the distribution of combustion reaction zone. The integral curves of CH* grayscale and temperature indeed confirmed this observation.