Mathematical modeling and analysis of cutoff impulse in a liquid-propellant rocket engine

Abstract

Thrust termination transient behavior of liquid-propellant rocket engines is important for launch vehicle to achieve the desired final velocity and, hence, fulfill the desired mission in placing a satellite in the intended orbit. A mathematical model has been developed for an open-cycle engine to predict the transient behavior of engine components, obtain the pressure changes of the combustion chamber, and to determine the cutoff impulse. By employing this model, the engine shutdown process has been simulated in four time intervals: (1) the duration from when cutoff command is issued to the time when the cutoff valves start to close, (2) closing of the cutoff valves, (3) discharge of combustion products from the chamber, and (4) the duration of the phase change and pressure fluctuations. The propellant flow has been modeled one-dimensionally in the cutoff valve and thermodynamically in the cooling channels and the combustion chamber. The results indicate that the time duration of the first two stages and the working pressure of the engine during the transmission of the cutoff command have considerable impacts on the increase or reduction of the thrust force. Also, with the improvement in modeling accuracy and the complete development of the engine processes, the results indicate a maximum error of 9% compared with the 15–41% error in the calculation of cutoff impulse achieved by previous works, which demonstrates the enhanced accuracy of the present modeling.