Performance Evaluation of a Diffuser –Ejector System using Cold Gas Thrusters with Different Nozzle Geometries in the Purdue Altitude Chamber Facility

In this paper, we investigate several cold gas thrusters with different nozzles geometries numerically and experimentally in the Purdue Altitude Chamber Facility where we use a diffuser-ejector system to simulate high altitude conditions. Here, the main aim is to study the effects of different thruster nozzle geometries and axial/radial gaps between the thruster nozzle exit and the diffuser inlet on the performance of the diffuser-ejector system. We used a two-stage ejector system to create the desired diffuser back pressure conditions at the exit of a second throat diffuser during the tests. Results to date focus on one of the thrusters having a highly truncated ideal contoured nozzle. While testing that cold gas thruster, we used the mass flow provided by the thruster as the suction load for the ejector system and completed its full performance characterization. We also studied the minimum starting, operating pressure ratios, and hysteresis behavior of the second throat diffuser. We obtained a noticeably small hysteresis region. We also found that the diffuser starting pressure ratio increased with increasing the axial gap between the nozzle exit and the diffuser inlet. Future work will consist of completing the tests for all the thrusters nozzle geometries. Furthermore, as we had used the same diffuser and the ejector system with a hybrid motor at simulated high altitude conditions, we compared the performance of the diffuser – ejector system with both hot and cold gas flows. By doing that, we can explore the effects of the specific heat ratio and the temperature of the exhaust gas flow on the diffuser-ejector system performance.