Combustion stability in a solid-fuel ramjet engine

A computational model is presented for a solid-fuel ramjet engine with an axisymmetric combustion channel in a fuel grain containing a wider section near the air inlet. The latter part of the channel serves as a flame holder where a recirculation zone develops providing necessary combustion stabilization. The model is based on RANS equations, with finite-rate chemistry in the turbulent gas phase flame taken into account. Reacting multicomponent gas equations are solved by a low-dissipation numerical scheme suitable for a wide range of Mach numbers. Solid fuel is gasified at the surface, and gasification products react in the core flow. Combustion of PMMA is studied numerically in the subsonic flow regime for different pressures, inlet velocities, and flame holder geometry parameters. It is shown that under certain conditions combustion in the engine becomes unstable, with flame blown off either in the main channel, or in the flame holder as well. Different combustion regimes are plotted as stability maps in the parameters space.