Experimental study of the effects of Weber number and recess length on the combustion characteristics for liquid-liquid swirl coaxial injector

The injector is a vital component of a liquid rocket engine that controls the atomization and mixing of propellant, which significantly on combustion performance. In this study, two liquid-liquid swirl coaxial injectors (LLSCI) with different recess lengths were developed, and the effects exerted by fuel (liquid methane LCH4) and oxidizer (liquid oxygen LOx) Weber numbers on combustion efficiency were examined by performing hot-firing test experiments. In addition, a heat transfer model of the combustion chamber was developed. By measuring the temperature at a spot on the combustion chamber wall, the temperature of any depth at that point and the temperature near the chamber wall could be deduced. The calculated results well complied with the experimental measurements and the maximum error was 5.8%. Furthermore, an investigation was conducted on the effects of Weber number and recess length on the combustion flow field of the internal mixing swirl coaxial injector. As indicated from the results, the combustion efficiency generally increased with the increase in LOx Weber number and the decrease in LCH4 Weber number. However, under the higher Weber numbers of the two propellants, the combustion efficiency and the gas temperature distribution were affected by the location of the combustion area and the degree of mixing. The combustion efficiency was elevated by 3.65% when the recess length increased by 2 mm. However, the high-temperature area of combustion close to the head would be caused, as well as ablation damage.