Static modelling of an open-cycle liquid-propellant rocket engine

Abstract

Ensuring that a rocket engine meets the mission performance requirements is critical for the successful operation of launch vehicles. Compliance with these requirements is verified through qualification tests. To reduce test costs and enable faster decision-making during development, establishing a high-accuracy engine model is a priority. Throughout the engine development process, subsystem performance may deviate from expected values. The cumulative impact of these deviations can drive overall engine performance outside the specified requirements. Therefore, maintaining traceability through modelling during the development phase and making corrective decisions based on model outputs are essential. In this thesis, an open-cycle liquid-propellant rocket engine is modeled. The model solves 16 nonlinear equations simultaneously to obtain 16 key performance variables that define the engine cycle. Once these key variables are determined, all remaining system performance outputs such as thrust, specific impulse, gas-generator temperature, and hydraulic pressure losses can be calculated. Using literature data, the model is applied to the KRE-075 engine and validated at the nominal design point. The largest discrepancy is observed in the gas-generator results and the turbine pressure ratio, reaching approximately 5 - 8%. This difference is attributed to the use of tabulated gas-property data from Huzel's book for the gas-generator solution under fuel-rich operating conditions. Under off-design operating conditions, variations in the positions of the control valves located in the gas-generator lines and in the thrust-chamber fuel line are investigated. For engine throttling, the most dominant effect is found to be driven by the gas-generator oxidizer control valve position, followed by the gas-generator fuel control valve position. Changes in the thrust-chamber fuel control valve position have a limited influence on the overall engine behavior. However, this valve is beneficial to trim the thrust chamber mixture ratio (O/F). The developed model produces solutions significantly faster than one-dimensional (1D) transient solvers and provides a detailed representation of the engine performance response to configuration changes. The model provides a practical, flexible and robust analysis for engine preliminary design stages. In this respect, the model is capable of supporting industrial engine development activities and can provide a common framework for both academic investigations and industrial design studies.