Experimental Investigation into Closed-Loop Control for HTPB-Based Hybrid Rocket Motors

Abstract

Space exploration greatly facilitates the development of advanced propulsion systems. Extensive research has shown that hybrid rocket motors have bright prospects for use in variable-thrust propulsion systems. However, the variable-thrust precision control of a hybrid rocket motor with a high-mass fraction of aluminum has not been adequately explored. In this paper, we propose a closed-loop control system for a high-performance laboratory-scale hybrid rocket motor, and verify its performance through tests on a hybrid rocket motor containing 98% hydrogen peroxide and hydroxyl-terminated polybutadiene with 58% of an aluminum additive. The results show that, first, the average value of thrust in the stable sections in the three stages were 400.7 N, 599.1 N, and 400.1 N when the target values were 400 N, 600 N, and 400 N, respectively. Second, the average thrust was stable, and the control error of the average value was better than 0.5%. Third, the real-time error in thrust was controlled to within ± 20 N with a steady-state error smaller than 5%. These results indicate that the proposed closed-loop control strategy for hybrid rocket motors with a high-mass fraction of aluminum can maintain a constant thrust and smooth transitions in case of variable thrust.

Bridging the Technology Gap: Strategies for Hybrid Rocket Engines

“…Guang et al [88] achieved 0.5% thrust control accuracy in a range of 400-600 N with an H 2 O 2 /PE (polyethylene) engine. The same group used closed-loop feedback of an H 2 O 2 HRE using 58% aluminized HTPB [89] with a control error of less than 0.5% and a steady state error of less than 5%, using thrust as the feedback parameter. These findings are similar to the results obtained by the same group using polyethylene [88], which is interesting because HREs with high percentages of aluminium show higher combustion instabilities, resulting in noisier feedback [89].…”

“…One of the biggest hurdles of closed-loop control for hybrids is that these methods typically rely heavily on the observation that the oxidizer mass flow or chamber pressure has a linear relationship to the thrust in smaller-scale motors [60,88,89]. For fast-regressing fuels such as paraffin, larger motors, longer burn times, deep throttling, or significant nozzle erosion, the linear relationship is most probably not valid any more.…”