In this study, an experiment was carried out to understand the behavior of incompressible flow passing through the plain-orifices of pintle injector in order to characterize the discharge coefficient (Cd) for different orifice geometries in an injector and show the flow passing through the orifice in different geometries of orifices. Three types of orifices, including primary orifices, secondary orifices, and film-cooling orifices, were utilized to characterize the discharge coefficient and to understand the flow pattern with high-speed imaging. Each of these orifices will be separated and tested in their test article. The impacts of parameters, including shape and size, on discharge coefficient, were studied. The discharge coefficient was determined for each test article by subjecting the orifices to a range of flow rates and measuring the pressure differential. The results obtained for the test article F show a good agreement with the choked fit curve. In contrast, other test articles' results show an inconsistency due to the cavitation phenomenon in their trends. However, they show that after the cavitation, they precisely follow the expected trends.Injection orifices are critical features for every liquid-propellant rocket engine injector. They play a significant role in controlling the engine's total mass flow rate, directly proportional to the resulting thrust. Injection orifices control the atomization and mixing of propellants, influencing the rocket engine's overall efficiency of combustion. Finally, they help prevent propellant backflow into the injector manifolds, where a fatal detonation could occur. It can be seen that the injector orifices play a significant role in determining an engine's and vehicle's performance. The injection orifices' general performance can easily mean the difference between reaching orbit and a failed launch for a full-scale company slated to place a payload into orbit.&nbsp;Methods of determining orifice discharge coefficient performance have been well known for many decades. However, orifice discharge coefficient measurements must be made for each specific design across the designed flow regime. Large-scale companies keep this information internal due to both proprietary and regulatory reasons. Also, injectors often have multiple orifice types and are evaluated as a lumped designs rather than individual orifice types. This makes finding pre-existing empirical data on a specific orifice challenging. A form of estimation must be involved during the initial design process when an exact design match cannot be found.&nbsp;&nbsp;&nbsp;&nbsp; Oregon State's High Altitude Liquid Engine (HALE) team will significantly benefit from independent flow testing of each specific orifice design currently planned for use in their next injector design. This is precisely what this study aims to do. Additionally, amateur engine designers, other schools, and startup launch companies may also benefit from this study's data.In this study, an experiment was carried out to understand the behavior of incompressible flow passing through the pintle injector orifices in order to characterize the discharge coefficient (Cd) for different orifice geometries. Hence, three different article tests were performed to investigate the influence of geometrical parameters on the discharge coefficient and flow pattern. Therefore, the primary conclusions of the study can be listed as:&nbsp; -&nbsp; A valid experimental method with an acceptable uncertainty level was used to characterize the discharge coefficient of injector orifices;&nbsp; -&nbsp; The results show that some designs are able to make cavitation and impact on the results we expected before the test;&nbsp; -&nbsp; The effect of precise manufacturing on characterizing plain-orifice would be critical and impactful on the results;&nbsp; -&nbsp; Using precise dimensional measuring methods led to a decrease in the uncertainty of the experiment.

The Influence of Plain-Orifice Geometry on Pintle Injector Flow Discharge Coefficient

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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