Modeling of supercritical-pressure turbulent combustion of hydrocarbon fuels using a modified flamelet-progress-variable approach

Non-premixed turbulent combustion at a supercritical pressure is an important physicochemical phenomenon in many propulsion and power-generation systems. In this paper, a modified flamelet-progress-variable model, in which a simple term is proposed to approximately account for the extra turbulent mixing related to large density difference between two fluid streams, has been developed and incorporated into a single-phase general fluid numerical scheme in RANS framework for solving supercritical-pressure turbulent combustion of hydrocarbon fuels. The model was validated and then applied for studying the coaxial injection and turbulent combustion of LOx/methane and the swirling injection and turbulent combustion of LOx/kerosene at various supercritical pressures. Results indicate that for the coaxial injection and combustion of LOx/methane at a mixture ratio of 3, flame length decreases as chamber pressure increases, dictated by the penetration capability of the injected LOx stream. For the swirling injection and combustion of LOx/kerosene at supercritical pressures, flame moves closer to the injector as chamber pressure increases. This phenomenon at a higher pressure is similar to that caused by an increased inlet-flow swirling number. It suggests that increasing chamber pressure may lead to a shorter combustor for the turbulent combustion of LOx and hydrocarbon fuels.