Impact of fuel injection temperature dynamics on the stability of liquid oxygen–methane supercritical combustion.

This article investigates the impact of fuel injection temperature on the stability of supercritical liquid oxygen (LOx)–methane combustion in a rocket-scale multi-element combustor using high-fidelity large eddy simulations (LES). It identifies a critical fuel injection temperature of 219 K below which the combustor exhibits self-sustained longitudinal acoustic instabilities characterized by high-amplitude pressure oscillations and altered flame dynamics. The study highlights the role of shear layer dynamics and the velocity ratio between fuel and oxidizer injection velocities as key factors influencing stability, with lower velocity ratios at reduced fuel temperatures leading to fuel accumulation, delayed combustion, and instability. Detailed spectral and dynamic mode decomposition analyses confirm the excitation of longitudinal acoustic modes in unstable cases, while stable operation is associated with nominal injection temperatures and higher velocity ratios. These findings provide essential insights for designing reliable, high-pressure LOx-methane rocket engines and establish a stability map linking fuel injection temperature and velocity ratio to combustion stability.