Liquid Propulsion Systems Centre (LPSC) has developed bipropellant engines employing hypergolic propellant combination of Nitrogen Tetroxide (NTO) as oxidizer and Monomethyl Hydrazine (MMH) as fuel for spacecraft applications. Coaxial swirl injector is used in these small engines. An experimental study was undertaken to evaluate the effect of non-uniformity of flow in the injector on the performance of the engine. Flow non-uniformity is determined by cold flow tests using simulant fluid and is expressed as standard deviation (SD) of fluid collected at specified distance from the injector face. The performance parameter, C star efficiency (C~*η) is determined by doing hot tests at sea level condition. Non uniformities were created on the outer flow (oxidizer) of the injector and cold & hot test evaluations were carried out at every stage. Test result shows that non-uniformity beyond a certain value has a direct bearing on the C~*η and any minor variation can cause C~*η change of 1.2% which accounts for approximately 4 sec in specific impulse for these category of engines. Measured throat temperature also showed a trend in line with C~*η.
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