Investigation of the Effect of Catalyst Granule Diameter on the Performance of Decomposition Chamber of a Hydrazine Catalytic Thruster

Monopropellant hydrazine thrusters are widely used in situation control, orbital transmission, and position correction systems of satellites. In these thrusters, hydrazine is decomposed into the hot gaseous products by passing through a catalyst bed during a highly exothermic reaction. In this paper, the decomposition chamber of a monopropellant hydrazine thruster is numerically simulated in the granule scale of the catalyst bed. The effect of the catalyst granule size is investigated on the performance of the decomposition chamber with catalyst bed with a length of 2.48 cm. Simulations have been performed for catalyst granules with diameters of 0.88, 1, and 1.15 mm at the porosity equal to 0.4 and the chamber inlet pressure equal to 15 bar. The results show that the size of the catalyst granules affects the chamber performance so that with its increase, the hydrazine decomposition and the bed temperature increase respectively 8% and 5% and the mass flow decreases about 25%, which in turn reduces the bed loading about 5%. Finally, further increase in the temperature of the decomposition chamber causes an increase in the outer wall temperature.