High speed optical diagnostics in a high pressure, GOX/RP-2 combustor

This paper presents the development and results from the application of optical diagnostics to a high-pressure GOx-RP-2 combustor. Its key objectives were to measure flame stabilization and flame position at realistic engine conditions. Experimental data was obtained at pressures from 300-2400 psi and mixture ratios from 2.9-20. Both chemiluminescence (OH∗ and CH∗ at 308-330nm and 420-432nm) and IR imaging (H₂O at 3.0μm and CO₂ 4.5μm) were employed for side on imaging of the flame. It was found that chemiluminescence imaging at realistic mixture ratios is only feasible at chamber pressures below about 500 psi, due to essentially 100% absorption by soot. Infrared imaging is possible at higher pressures, although it is also reduced in intensity with increasing chamber pressure. These results show that the flame spreading angle ranges from approximately 6-14 degrees, varying with pressure and mixture ratio. A novel borescope was used to image the flame from upstream of the GOx post, enabling visualization of the flame stabilization location. These results show that the flame is anchored near the GOx post for essentially all the experiments. At higher pressures, helical spirals of luminosity near the GOx post are evident, apparently tracing the swirling fuel patterns before more distributed luminosity is observed.