Systematic strategies for thermochemical model reduction in rocket propulsion applications

Standard propulsive applications, such as liquid and hybrid rocket engines, are characterized by highly turbulent purely non-premixed flames. Mixing and combustion of propellants occur under severe thermodynamic conditions, and the numerical characterization of such class of devices is made difficult by the highly non linear thermodynamic and transport properties of the reacting mixture. In this framework, reliable simplified/skeletal chemical kinetic mechanisms and accurate calculation of thermochemical properties, are required for high fidelity simulations. With the present work, the well established computational singular perturbation-based simplification strategy, is employed in a broader range of thermodynamical conditions characterized by supercritical pressures. A systematic framework for chemical kinetics simplification under supercritical conditions is provided and its capabilities are assessed for paraffin/oxygen flame structures, representative of the combustion processes taking place in paraffin-based hybrid rocket engines. An 18-species skeletal mechanism for paraffin-GOx is obtained starting from a 76-species detailed mechanism.