Effect of Multicoaxial Injectors on Nitrogen Film Cooling in a GCH4/GO2 Thrust Chamber for Small-Scale Methane Rocket Engines: A CFD Study

Improper film cooling design and positioning of an injector in the face plate cause thermal damage to the thrust chamber wall and lead to rocket engine failures. An experimental combustor with five shear coaxial injectors was damaged owing to inadequate film cooling distribution on the thrust chamber wall. The present study aimed to simulate the experimental test case and investigate the causes of the thermal damage. In the simulation, gaseous methane and oxygen were injected at the inner and outer inlets of the shear coaxial injectors and nitrogen, used as the coolant, was injected near the upstream of the chamber wall. The turbulent chemistry interaction was modeled using a reduced DRM-19 mechanism by incorporating the Eddy Dissipation Concept model. Numerical investigations were conducted to examine the cause of thermal damage. The temperature contours of the thrust chamber wall were compared with the experimental image of the damaged wall. Further, simulations of single-row (SR) and multi-row (MR) injector configurations were conducted to assess the effect on film cooling distribution. The adiabatic film cooling effectiveness and specific impulse were determined for all simulated cases. The results showed that MR simulations with narrow injector angles had poor film cooling performance, while wider angles led to lower specific impulse. The face plate with an angle of 15 degrees between the injector positions showed better performance in terms of considering both the film cooling and specific impulse.