Thrust Prediction Model for Varying Chamber Pressure for a Hypergolic Bipropellant Liquid Rocket Engine

Thrust developed in a rocket is mainly a function of the chamber pressure developed in the combustion chamber and thrust amplification factor (Cf) due to expansion of hot gases in the nozzle as long as the ambient pressure remains constant. For a liquid propellant engine, chamber pressure can be varied by altering the feed pressure, and its applications are in the blowdown or throttling mode of operations. Cf will also vary with chamber pressure as flow separation in divergent nozzle gets altered. A study has been carried out to develop a model to predict the thrust of a hypergolic bipropellant engine for varying operating chamber pressure at the same ambient pressure condition. Engine considered for the study is of medium thrust range. A mathematical model was developed from first principles to predict the thrust of the engine for varying chamber pressure for the same ambient pressure condition. Prediction was made from 100 to 50% of the maximum thrust. The model was validated based on sea level hot tests for 10 s each with thrust measurement, and the variation in thrust was achieved by altering the feed pressures. The results were found to be in close agreement with the predicted performance, and the maximum deviation was found to be 3.0%. This paper gives the details of the study carried out.