Flow characteristics of a pintle injector element

The flow characteristics of a pintle injector element were studied by theory and experiments. A spray angle model was firstly proposed based on our previous work, and then a model on the discharge coefficient of the orifice was also derived. Then, experiments were conducted by a pintle injector element which was simplified from pintle injectors with discrete radial orifices. Snapshots of the sprays were captured by using backlit photography technique. Results show that the pintle injector forms an arched cloak-like spray. The spray pattern and breakup are heavily related to the local momentum ratio and Reynolds numbers of jet and film. The spray angles obtained from the snapshots coincide with theory well. Meanwhile, a semi-empirical model of discharge coefficient of the orifice was proposed based on the experiments. It is found that the spray angle and discharge coefficient are dominated by the local momentum ratio. The spray angle and discharge coefficient increase along with local momentum ratio and tend to be stable for large local momentum ratios. Besides, discharge coefficient of the orifice is also found to be slightly affected by the ratio of jet diameter to film thickness.