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Design of a pintle injector

Erkal, Berksu
Pintle injector design methodology for liquid oxygen/gaseous methane rocket engine is investigated with this study. Cold flow experimental work is conducted with water and air to investigate the characteristics of designed injectors by observing spray formations. 750N at maximum thrust with 3:1 throttle ability is chosen as mission requirement. 3 different reservoir geometries are manufactured and experimental investigation is conducted to ensure uniform and axisymmetric spray cone. After decision of the final reservoir, 6 different injectors are designed which are combination of 3 different pintle angles and 2 different annular gap thickness. Non-dimensional parameters from literature are used to determine water and air mass flow rates of cold flow experiments. Phase Doppler Particle Analyzer (PDPA) is utilized to obtain droplet Sauter mean diameters (SMD) and velocity profile in axial and radial direction within the spray. These experiments are carried out for 3 different throttle level for all injectors designed. Spray half cone angles are measured by high speed camera and high contrast images are obtained for post processing observations. At studied flow rates recirculation zone is obtained only for 20° instead of 30° and 40° pintle angles and Sauter Mean Diameter (SMD) increase is experienced at the end of these recirculation zones. Moreover, wider spray half angles up to 58° are obtained with the pintle angle of 20°. SMD values are in the range of 20-50 μm for all injector types at recirculation zones and injectors with 20° pintle angle have the lowest SMD values compared with the other injectors.