Technical Analysis of a Nitrous Oxide and Ethanol Electric Pump-Fed Rocket Engine

The traditional Gas Generator Cycle (GGC) and Turbo-Pumped Cycle (TPC) rocket engines introduce additional mechanical complexity to liquid rocket engines, which contain more risks, maintenance costs, and launch failure. The Electric Pump-Fed (EPF) engine presents a simplified alternative, using batteries, an inverter, and an electric pump to drive liquid propellants. This study focuses on designing and evaluating a 5,000 N thrust EPF-class using Nitrous Oxide (N₂O) and Denatured 98% Ethanol (E98) as propellants. The proposed engine consists of a co-axial regenerative cooling nozzle, a liquid N₂O / E98 torch igniter, a multi-slit pintle injector, and electric pump-fed hydraulic systems. The study will discuss the following major evaluations: 1) Sizing and design of key components, 2) nozzle thermal behavior, and 3) development of fluid Simulink hydraulic schematics and flow simulations. In sizing and design of key components, this study will focus on the overall approaches and analysis of the geometrical design of the nozzle, test stand, pintle injector, and centrifugal pump. The engine nozzle of this study is a converging-diverging (CD) co-axial design with two primary layers, the inner (C101) copper and outer (6061 aluminum), that allows for both film-cooling and regenerative cooling. Upon the nozzle, a multi-slit pintle injector and an igniter are attached, which is crucial to ensure immediate combustion during firing. The centrifugal pump was designed to pressurize ethanol, which involves a pump impeller driven by a brushless direct current motor (BLDC) system coupled with a gearbox for precise target torque and angular velocity. This design was chosen to bypass complex spin start cycles used in traditional gas generator engine cycles and other design complexities. Since an electrical system is used in place of a gas generator, this study will examine the implications of how feasible a motor gearbox-driven pump system can be scaled to the industrial level. Next, a comprehensive thermal analysis is conducted to verify the feasibility of a hybrid nozzle cooling mechanism that employs both regenerative and film cooling. Excel and MATLAB models were used to analyze steady-state and transient nozzle temperature behavior and determine the peak temperatures achieved at the inner surface of the combustion chamber, nozzle throat, and nozzle exit. The nozzle thickness was sized to minimize thermal stress due to thermal gradients from the resultant nozzle temperature distribution. A Simulink model based on the engine’s piping and instrumentation diagram (P&ID) uses calculated engine geometrical parameters to simulate the EPF engine performance during a static fire test event. The simulation results in the behavior of the propellants traveling in the feed line, electrical system (involving the centrifugal pump, motor, and battery), engine propulsion performance, and power efficiency. However, this study will not cover information regarding actual static fire tests, which will be conducted in the future. The results of the engine simulation will be evaluated based on its performance compared with other similar GGC and TPC-class rocket engines.