Supercritical LOX/methane flame stabilization and dynamics of a shear coaxial injector

The mixing and combustion of liquid oxygen (LOX) and gaseous methane of a shear coaxial injector operating under supercritical pressures have been numerically investigated. The near field flow and flame dynamics are examined in depth, with emphasis placed on the flame stabilization mechanisms. The model accommodates the full conservation laws and real-fluid thermodynamics and transport phenomena over the entire range of fluid states of concern. Turbulence closure is achieved using a large-eddy-simulation technique. The injector flowfield is characterized by the evolution of three mixing layers originating from the trailing edges of the two concentric tubes of the injector. As a consequence of the strong inertia of the oxygen stream and light density of methane, a diffusion-dominated flame is anchored in the wake of the LOX post and propagates downstream along the boundary of the oxygen jet. The overall flow development is largely determined by the lighter methane stream. The large-scale vortices shedding from the outer rim of the LOX post engulf methane into the wake recirculation region to react with gasified oxygen. The frequencies of vortex shedding match closely those of a flow over a rear-facing step, mainly due to the large density disparity between LOX and gaseous methane. The effects of the momentum-flux ratio of the two streams are also examined. A higher-momentum methane stream enhances mixing and shortens the potential cores of both the LOX and methane jets.