Analyzing combustion performance of LOX/GCH4 pintle injector according to spray characteristics

This study aims to reveal the influence of Local Momentum Ratio (LMR) on the combustion efficiency of an LOX/GCH4 pintle injector from the perspective of spray characteristics. Hot fire tests were conducted to establish the relationship between combustion efficiency and LMR. The spray characteristics for different LMRs were simulated by the validated volume of fluid-to-discrete phase model method, taking into account the combustion chamber wall confinement. Subsequently, the difference in combustion efficiency was analyzed by comparing the spray simulation results of backpressure conditions similar to hot fire tests. The results indicate that combustion efficiency increased initially (LMR = 1.12 - 1.64) and then decreased (LMR＞1.64). Quantitative analysis revealed a linear correlation ( R 2 = 0.95) between LMR and combustion efficiency within 1.12 < LMR < 1.64. As the LMR increased, the improvement in combustion efficiency was attributed to a wider spray distribution range and smaller droplet sizes. The area of the mantle recirculation zone that is detrimental to combustion decreased by approximately 38%, and the droplet size reduced from 37 μm to 16 μm. This effectively enhanced both the mixing of the propellant and the evaporation process. When the LMR exceeded the critical value (1.64 in this study), the impingement of liquid oxygen on the combustion chamber wall was confirmed via overheating discoloration marks on the inner surface of combustion chamber’s cylindrical section. The impingement of liquid oxygen on the combustion chamber wall increased the transport of liquid oxygen to the wall, directly reducing the mixing quality and combustion efficiency. The outcomes of this study provide the practical guidance for design and improvement in combustion efficiency of the pintle injector thrust chamber.