Erosive burning modelling on solid rocket motors. Application to development of SRM 120

摘要

Solid rocket motors are still preferred for a variety of missions due to their simplicity, high reliability and relatively low cost when compared to other propulsion methods. Various solid rocket motors models have been developed in order to allow their accurate design. Key performance parameters have been investigated and various geometrical solutions have been chosen in order to increase the performance of a given solid rocket motor. The key parameter in such models is the burn rate and its accurate prediction in the pressure and temperature conditions available inside combustion chamber. We have undertaken the development of a 120 mm solid rocket motor (SRM 120) for a suborbital vehicle. The motor aims at producing around 7000 Newtons for almost 6 seconds of burn time while using a steel combustion chamber with filleted end-cap and nozzle. The propellant has a cylindrical geometry with a central burning core and it is composed of 10 identical segments. Details are given on both the construction and the firing test preparation of the motor since this represents important knowledge for the subsequent operation of the motor. The thrust curve is measured together with key performance parameters on a horizontal test stand. An internal ballistic model is developed for SRM 120 with the aim to accurately its performance parameters. The model incorporates both start-up and tail off phases, including the start-up using pressure membrane as used on many solid rocket motors. The burn rate is first shown to depend only on pressure and comparison between theoretical and numerical data is done. Comparison is done with test stand measurements and sign of erosive burning is indicated. A model for erosive burning is described and implemented within the abovementioned internal ballistic model. Further we change the numerical model to incorporate the erosive burning and compare again numerical results with the experimental measurements. We show good agreement between the numerical results and experimental data and indicate methods through which negative impact of erosive burning can be diminished.