The hydrodynamic design and analysis of an RP-1 pump for a liquid rocket engine.

Abstract

South Africa has a fledgling satellite industry but lacks the ability to launch spacecraft into low Earth orbit. As a result, the University of KwaZulu-Natal’s (UKZN’s) Aerospace Systems Research Group (ASReG) began the development of the South African First Integrated Rocket Engine (SAFFIRE). SAFFIRE aims to be a versatile, small scale, liquid rocket engine capable of being clustered for use on small-satellite (‘small-sat’) launch vehicles. The propellants for the proposed engine are Rocket Propellant-1 (RP-1) and liquid oxygen (LOX), which are fed into the combustion chamber via the injector. The uniqueness of SAFFIRE lies in the use of electrically driven pumps (‘electropumps’) as opposed to the conventional turbopump design. The electropump system has the fuel and oxidiser pumps independently housed and driven by brushless DC motors, which draw power from a lithium-polymer battery pack. A hypothetical launch vehicle was proposed to validate design specifications for the SAFFIRE engine, from which the hydrodynamic requirements of the electropump system were obtained. A meanline design algorithm was developed, using conventional design methods for centrifugal pumps. The algorithm was constructed to simultaneously meet the hydrodynamic system requirements of the engine, minimize the potential of cavitation at the fuel pump inlet and maximize the operational speed to minimize the overall pump weight. The hydrodynamic requirements of the system result in a low specific speed design, thus placing the pump in the region between full emission centrifugal pumps and positive displacement pumps. The low specific speed presented unique problems, not commonly encountered via the conventional pump design method, such as excessively small blade exit widths that are sensitive to dimensional variations. The Barske pump was investigated as a potential solution; it is a partial emission pump with the meanline design being governed by vortex theory. A comparative analysis between the conventional and Barske design was done using computational fluid dynamic techniques. The final hydrodynamic design is a hybrid between a Barske impeller and a scroll collection volute, which is typically found on a full emission pump. An investigation was done to determine an appropriate solution for mitigating the cavitation. It was found that the initial 3 bar tank pressure, suggested by literature, is applicable for an equivalent engine utilizing a turbopump system. The optimal tank pressure for the electropump system was found to be 9 bar. This increased available pressure head at the inlet of the pump eliminated any form of cavitation. The hybrid pump delivers 62.12 bar of pressure at a mass flow rate of 2.75 kg/s with a 62.12 % efficiency.