Design and Test of a Swirling Nitrous Oxide Injection System for a Hybrid Rocket Engine

Design and Test of a Swirling Nitrous Oxide Injection System for a Hybrid Rocket Engine In this work we design an innovative swirling injection system for the N2O hybrid rocket motor of the Department of Mechanical Engineering at the California Polytechnic State University, San Luis Obispo (CalPoly). The past firing tests of the motor were conducted with both cylindrical and annular grain geometries and with axial injectors in a shower-head configuration. Various orifice diameters and number of injectors were employed in different tests, but in all cases the post-burn analysis of the fuel grains showed a non-uniform regression rate along the grain length, with an increased consumption of the solid fuel at the upstream end of the motor. Thus, one of our goals is to improve the homogeneity of the burn axially along the grain. With the purpose of obtaining a uniform regression rate along the port length, we propose a new injection system for the motor. Our aim is to employ both the effects of the jet impingement of the oxidizer on the grain and of the swirling flow of the propellant in order to enhance the regression rate in the back part of the solid fuel. The idea is to aim half of the injectors, placed at the upstream end of the motor, directly towards the inner fuel surface of the rear region of the grain. The injectors are also inclined with respect to the radial direction of the circular port section, in order to induce a swirling motion of the oxidizer in the region that follows the impingement point. Basically, the goal is to avoid interacting with the solid fuel in the leading-edge region of the motor, and impinge directly onto the rear grain. Here, the component of the velocity of the impinging jet tangential to the circumference of the fuel gives rise to the rotational motion in the following part of the combustion chamber. In this way, the combined effects of the oxidizer jet colliding on the grain surface and the induced swirl in the rear-end of the combustion chamber cause an enhancement of the heat transfer to the fuel surface and consequently an increase in the local regression rates.