Assessment of using electric pumps on hybrid rockets

Abstract

In small hybrid rockets, liquid oxidizer is fed into the combustion chamber by pressurizing the oxidizer tank to achieve the desired injector pressure. However, larger applications employ propellant pumps to keep the propellant tank mass at reasonable levels. Conventionally, pumps are implemented on rockets by means of turbopumps. However, turbopumps are complex systems with serious development time and costs. With the current advancements in batteries and electrical machinery, pumps driven by electric motors become viable actors. In the case of hybrid rockets, operation of a single liquid propellant with a single pump has significant advantages compared to their use in the bipropellant liquid engines. In this paper, an example case of an upper stage hybrid rocket system is introduced and a propellant pump is designed using CFD modeling. The advantage of using electric motor driven pumps has been established via weight analysis and a comparison between alternative feed systems. Turbopump system is not considered due to its complexity as an alternative system. Therefore, comparison is limited to the cold gas pressurization feed system. It has been shown that a significant advantage in total feed system weight is achieved not only with a high-head pump but also with a low-head pump with assistive pressurization. A 69.9 % mass reduction for double-stage pump system and a 45.2 % mass reduction for the single-stage pump system was calculated compared to the reference pressure-fed system.