The Effect of internal geometry of the fuel injector of a 10N Monopropellant Hydrazine Thruster on the outlet liquid sheet characteristics

Hydrazine monopropellant thrusters are most widely used for navigation and control systems of re-entry and manned payloads. In this paper, the effect of the internal geometry of the injector on the characteristics of the outlet liquid sheet, such as the liquid sheet thickness, the spray cone angle, the average output velocity, and its mass flow rate, has been studied. The injector chosen for the case study is the fuel injector of a 10N monopropellant hydrazine thruster. This injector was designed in such a way to achieve a medium spray angle and a very small sheet thickness, which is suitable considering the limited length of the catalytic chamber and leads to finer atomization. For this purpose, simulation of the internal flow based on the computational fluid dynamics is performed to predict the output flow characteristics, and then parametric studies are conducted to investigate the effects of geometry. The results of these studies show that the internal structure of the injector has a great influence on the control of the characteristics of the liquid sheet, and the ratios of fluid swirl radius to the nozzle radius/inlet duct radius have the greatest effect on the output spray characteristics, so that minimum average speed is achieved at larger ratios and maximum average speed is obtained at smaller ratios.