Numerical and experimental investigations of single-element and double-element injectors using gaseous oxygen/gaseous methane

The objective of this study is to investigate the effects of fuel/oxidizer (F/O) momentum ratio on the mechanism of mixing and combustion of single-element and double-element shear coaxial injectors numerically and experimentally using gaseous oxygen/gaseous methane (GO₂/GCH₄) and non-intrusive optical diagnostics technique based on planar laser induced fluorescence (PLIF). Instantaneous OH-PLIF images demonstrate that the flame with higher F/O momentum ratio exhibits appearance characteristics with more obvious wrinkled shear layers, extinction and kernels events. Simulation and time-averaged results show that with the increase of F/O momentum ratio at the condition of fixed total mass flow rate, the initial combustion position becomes closer to the front of the chamber. The large mass flow rate of the double-element combustor is beneficial to the thermal protection of the chamber wall. Based on the high-speed images and velocity distribution obtained from numerical data, it is detrimental for the propagation of the flame front at the injection condition of high F/O momentum ratio. In addition, according to the infrared thermal pictures, the flame outside the chamber becomes broader with the increase of F/O momentum ratio, and the plume of double-element combustor will challenge the thermal protection around the equipment. Moreover, new methods are applied in this paper to extract the flame boundary of the OH-PLIF diagrams and to calculate the number of the pixels of the plume from infrared thermal imager results.