Development of a non-intrusive flame to fuel surface radiative heat flux measurement for hybrid rockets

Radiative heat transfer from the flame to fuel surface has dominating effects over convective heat transfer on the regression rates in hybrid rockets with low oxidizer fluxes. Often, these effects are neglected or modeled with ad-hoc definition of soot radiation. Since the temperature of the flame in hybrid rockets is very high, intrusive measurements of temperature and radiative heat flux is very difficult and inaccurate. In this study, a recently developed non-intrusive flame to fuel surface radiative heat flux diagnostic for the upward flame spread is extended to a 2D slab motor hybrid rocket. This diagnostic relies on the two-color pyrometry technique and utilizes a high-speed camera to measure the flame field temperatures. A 3D flame volume hull is reconstructed that enables soot volume fraction measurement. The measured flame temperature and soot levels are further utilized in a 3D ray-tracing algorithm to obtain the flame to fuel radiative heat flux. The estimated radiative heat flux is compared to previously reported values and found to be in good agreement.