Journal of Propulsion and Energy ISSN:2734-1887(Print) 2765-0049(Online) Free Open Access International Journal on Propulsion and Energy Science and Technology

Three different types of injectors, specifically inner closed/outer closed, inner open/outer open, and inner screw/outer screw bi-swirl coaxial injectors for a 420 N-class bipropellant (monomethylhydrazine as a fuel and dinitrogen tetroxide as an oxidizer) thruster, were designed to satisfy the injector design requirements (injection pressure drops and spray cone angles) at the same mass flow rates. An experimental study has been carried out to compare the spray characteristics of these injectors. Injection pressure drop, discharge coefficient, spray cone angle, and vertical breakup length were measured by independently changing the inner and outer mass flow rates. Discharge coefficient data through the inner and outer swirl injectors remained almost constant regardless of mass flow rates and injector types. For all of the injectors, compared to those under single-injection, the inner spray cone angle under bi-injection was greater and the outer spray cone angle was smaller. The spray cone angles were affected by variations in the inner and outer mass flow rates. For all of the inner and outer injectors, the vertical breakup length of liquid sheets decreased with increasing mass flow rate. The breakup length was also influenced by the injector type. A novel empirical equation for the breakup length of a swirl injector considering the effects of operating conditions and injector geometries is suggested.