Simplified numerical simulation model for hydroxyl ammonium nitrate-based monopropellant rocket engines

Abstract

A simplified model is proposed to simulate the working process of hydroxyl ammonium nitrate-based monopropellant rocket engines. The porous medium model and volume-of-fluid model are used to solve for the internal flow field of a monopropellant engine containing a catalyst bed to emphasize the establishment of a propellant decomposition model. The decomposition process is assumed to be separable into mass transfer and quick energy release processes. The mass transfer process is described by a two-stage decomposition model that combines catalytic and thermal decompositions according to temperature. This paper explains how to implement the two-stage decomposition model by using a titration experiment and thermal decomposition data. A detailed example is provided involving the calculation of the steady-state flow field of a 150-N monopropellant rocket engine in FLUENT. The results obtained using only the catalytic decomposition model and the two-stage decomposition model were compared with those of hot-fire tests, and show that the two-stage decomposition model is accurate. The combustion chamber pressure obtained from two- and three-dimensional simulations for the flow field of the engine agreed with the results of hot-fire tests. The calculated external wall temperature of the lower catalyst bed was slightly higher than the measured temperature, whereas the external wall temperature of the upper catalyst bed was close to the measured values.