Nonlinear Combustion Instability in a Multi-Injector Rocket Engine

What is it about?

The combustion instability mechanism is very complex due to the nonlinear dynamics system involving the possible injector-to-injector interactions and interactions with the feed system and upstream manifold. To better understand the effect of pressure disturbances on the stability of the reacting flow in a rocket engine combustor with multiple injectors and a choked nozzle, a computational study is performed in this paper. The open-source Computational Fluid Dynamics (CFD) software, OpenFOAM, is used for this study. The study is conducted for a choked nozzle combustion-chamber with 10- and 19- coaxial injector ports. Spontaneous and triggered longitudinal instability modes can be observed for the 28cm diameter combustion chamber. For the larger diameter 43cm combustion-chamber, different solutions are obtained with different inlet mass flux pulsations. A longitudinal instability occurs for the cases without propellant flow pulsation and with moderate magnitude inlet mass flux pulsation. The tangential instability is triggered when the magnitude of the inlet mass flux pulsation is greater than the threshold value. The two different instability modes result in two different combustion patterns in the chamber. The large amplitude tangential pressure wave oscillation enhances the mixing by generation of streamwise vorticity and the fuel burning efficiency, which results in the higher time-average temperature and pressure inside the combustion-chamber. In the last session, a similar combustion instability for the 28cm diameter combustion-chamber with 10- and 19-injector is obtained by preserving the mixing rate parameter.

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