Multi physics modelling for a hybrid rocket engine with liquefying fuel: a sensitivity analysis on combustion instability

Hybrid rocket engines represent a promising alternative to both solid rocket motors and liquid rocket engines. They have throttling and restart capabilities with performance similar to storable liquids, but are safer and are low-cost. However, some drawbacks, such as low regression rate and combustion instability, are limiting their effective application. Paraffin-based fuels are a solution envisaged to face the low regression rate issue, and the capability to describe and predict combustion instability in the presence of liquefying fuels becomes an enabling step towards the application of hybrid rockets in next-generation space launchers. In this work, a multi physics model for hybrid rocket engines is presented and discussed. The model is based on a network of submodels, in which the chamber gas dynamics is described by a quasi-1D Euler model for reacting flows while thermal diffusion in the grain is described by the 1D heat equation in the radial direction. The need to introduce strong modelling simplifications introduces a significant uncertainty in the predictive capability of the numerical simulation. For this reason, a sensitivity analysis is performed in order to identify the key parameters which have the largest influence on combustion instability. Results are presented on a test case which refers to a paraffin-based grain burnt with hydrogen peroxide.