Generation mechanisms of high-amplitude pressure oscillations in a high-pressure gaseous H2/O2 rocket-type combustor with low-temperature hydrogen injection

This study investigates high-pressure H2/O2 combustion in a single-element rocket-type combustion chamber using two-dimensional direct numerical simulations. The objective is to identify the conditions that lead to severe pressure oscillations by analyzing variations in injection velocity ratio and mixture ratio, in combination with low-temperature fuel injection, and to elucidate the underlying mechanisms. The compressible Navier–Stokes equations with a detailed chemical reaction mechanism are employed. The combustion chamber is modeled as a two-dimensional planar configuration with a divergent nozzle to enable comprehensive parametric studies. Results indicate that unstable combustion cases generate intense pressure waves, with peak amplitudes reaching approximately 60 bar, which is about 2.5 times higher than the target combustion pressure of 24 bar. These severe oscillations are primarily attributed to the accumulation of unburned H2 near the injector, which enlarges the non-premixed flame area, increases heat release, and consequently amplifies the pressure waves. Conditions characterized by low velocity ratios and low mixture ratios, in conjunction with low-temperature hydrogen injection, are found to promote this accumulation and thereby trigger the onset of high-amplitude pressure oscillations.