Measurement of annular liquid film thickness in an open-end swirl injector

An electrical conductance method was used to measure the liquid film thickness formed in an open-end swirl injector which is commonly used in Russian liquid-oxygen (LOX)/kerosene engines such as RD-120, RD-170, and RD-180. Two porous titanium electrodes and signal processing circuit based on lock-in amplifier were designed to measure the rapid variation liquid film thickness. The experimental results show that the liquid film thickness in the injector decreases with the increase of the pressure drop. The results of these measurements were compared with theoretical equations for predicting liquid film thickness in a swirl injector. An empirical equation to predict liquid film thickness in open-end swirl injector was modified based on the experimental results. Agreement between the modified equation and experimental results is demonstrated in this paper. This measurement method was also used to measure the liquid film thickness under pulsating conditions, and the study shows that our proposed method can be used to measure the liquid film thickness not only in the steady condition but also in the pulsating condition.