A simplified design methodology for coaxial swirl injector

Abstract

Gas-liquid coaxial swirl injectors are widely used in advanced hydrogen/oxygen rocket engines and hydrogen/oxygen/hydrocarbon tripropellant engines. The design quality of injector is very important to the performance, stability, reliability and life-span of the liquid rocket engine. A simplified flowrate characteristics based methodology for the design of coaxial swirl injector is presented in this paper. The design methodology of coaxial injector is based on the flowrate theory of liquid centrifugal injector and gas dynamics. Owing to the correlative experiment and theoretical analysis, the interaction between the liquid and gas phases in the injector is relatively small with common recess ratio values. The simplified approval to design the coaxial injector is to calculate the fluxes of liquid and gas phases respectively, and then revise them by experiments. The liquid flux is firstly computed by the flowrate theory of classic liquid centrifugal injector, and then calibrated through the flux coefficient ///. While the gas flux is computed by the gas dynamics of annulus passage according to its flow state. A modify coefficient //, is necessary because of interaction between the central liquid flow and the outer gas jet, and of the influence of gas viscosity. The modify coefficient should be chosen through comparison between theoretical and experimental results on flowrate characteristics. The methodology has been verified by cold experiment using air and water as analogy media, and been applied to the design process of a GO2/kerosene rocket engine. The results of the direct GO2/kerosene cold experiment and the hot tirt test of that GO2/kerosene rocket engine show the design is successful. 1. The coaxial swirl injector The schematic of the investigated injector is shown in Fig.I . It is widely used in the advanced Lox/LH2 rocket engines and the tripropellant engines for next generation space mission. It consists of a liquid central tube and a gas annulus passage. The swirling liquid flows out of the central tube and the gas jet injects through the annulus. Compared with other injectors, the coaxial swirl injector has the characteristics of finer spray, shorter atomization distance and more uniform mixing. There exists interaction between the gas jet and the liquid flow of the injector. The extent of this kind of interaction depends on the configuration parameters of the injector and the injecting working parameters such as injecting pressure drops. Fig. 1 Schematic of coaxial injector The recess ratio (RR) is an important special configuration parameter of the coaxial injector. It is defined as the ratio of the recess length of the central liquid nozzle over the entrance diameter D// of the outer gas annulus: