Impact of chemical modeling on the numerical analysis of a LOx/GCH4 rocket engine pintle injector

Liquid rocket engines equipped with LOx/GCH4 pintle injectors represent a promising technology when a large throttling capability is required. Still, limited amounts of data are available in the literature about the numerical characterization of pintle injector configurations under reacting conditions, with the entirety of these studies resorting to global or quasi-global reaction mechanisms. To this end, the objective of the present work is to assess the impact of chemical kinetic modeling on the prediction of major combustion observables, thermal flow field, and gas-liquid interaction in a pintle configuration of interest. Specifically, we carry out three unsteady Reynolds-averaged Navier–Stokes simulations under an Eulerian-Lagrangian fashion through variable-fidelity kinetic schemes, namely, one quasi-global scheme and two skeletal schemes derived from the high-pressure Zhukov's detailed mechanism. On the one hand, employing quasi-global chemical kinetics delivers an inconsistent flame topology. On the other hand, the overall combustion characteristics remain unaltered regardless of the skeletal mechanism complexity, while significant discrepancies can be envisaged in the flame dynamics. Moreover, the computational burden exponentially increases with mechanism size, preventing high-fidelity skeletal schemes from being leveraged in design-oriented computational fluid dynamics. Based on these findings, quasi-global chemical kinetics should be discarded when targeting high-pressure rocket engine conditions, while ad-hoc optimized skeletal mechanisms should be developed. This way, the present study provides an insightful contribution to identifying the optimal complexity of chemical kinetic modeling to ensure reliable, still cost-effective numerical simulations of liquid rocket engine combustion devices.