To evaluate the radiative heat impact of hybrid rocket exhaust plumes on surrounding components in small spacecraft propulsion systems, this study investigates a non-contact flame temperature estimation method using a color high-speed camera. A calibration experiment using electrically heated resistive wires was conducted to derive the relationship between RGB intensity ratios and temperature. The results confirmed that the g/r ratio increases with temperature and serves as a qualitative indicator under fixed camera settings. Subsequently, a ground combustion test of a GOX/HDPE hybrid rocket was performed. The temporal variation of the g/r ratio obtained from flame images was compared with theoretical flame temperature profiles calculated from O/F history using RocketCEA. The observed g/r ratio trends were generally in agreement with the theoretical predictions. Meanwhile, radiative heat flux measured with a heat flux sensor showed a significant increase over time, suggesting that changes in emissivity due to soot or high-temperature gas had a greater effect than temperature variation alone.
ICHIHARA et al. (Wed,) studied this question.