In this section, our cold-flow testing campaign will be outlined. Here is a summarized timeline of the machining and corresponding cold-flow testing we will do before hotfire (more detailed descriptions can be found in the child pages):

  1. Manufacture a mock pintle center body (literally just an aluminum cylinder with slots). Run CO2 through the system with a pressure equal to the pressure drop (the CO2 will be emptying into ambient pressure). Use the depletion time of the CO2, data from the PT, and the injection area to calculate Cd of the slots. Plug that Cd into the calculations and make a second version of the injector test piece with modified slot heights. Cold flow with CO2 again to confirm that your Cd is what you predicted this time. In this way, fundamental engine parameters like the mixture ratio or mass flow rates don't have to change – instead, just change the injection area until the desired mass flow is achieved. 
  2. Manufacture the injector baseplate, as well as the steel pintle center body (no pintle tip yet), as well as a mock part that surrounds the baseplate where we can inlet fuel into, which will be replaced with water for this test. Since we won't have the combustion chamber yet, we can use this mock part to inject the water. Once again, we will inlet this water at a pressure equal to the pressure drop across the fuel during hotfire, since it will be exiting out to ambient air. The objectives of this test will be to characterize mass flow, Cd, and the injection quality of the annular gap. We also aim to see if there is any misalignment with the center body and baseplate that would affect annulus flow. Characterizing mass flow and Cd will be similar to testing with the CO2. If our resultant Cd results in a mass flow rate that is too low, we can put the baseplate back on the lathe and take off another thou. If it results in a mass flow rate that is too high, we may just accept a slightly more fuel rich mixture ratio.
  3. Bore out the mock part slightly so that film cooling holes are exposed. Then, inlet the total massflow of fuel to verify that film cooling massflow is what you expected. Make sure to only drill out film cooling holes after mass flow out of the annulus is verified in 2. 
  4. Calibrate throttle valves by performing multiple single fluid cold-flow tests and actuating the ball valves to various degrees. For the CO2, we will offset the greater pressure drop by removing orifices. For the IPA, we will test at a manifold pressure equal to the nominal injector dP + ambient pressure so that the IPA injector sees the same pressure drop across it. Both of these methods will ensure the flow through the nitrous and IPA injectors will be roughly equal across cold flow and hotfire.
  5. Do a two-flow test with CO2 and water with the mock injector part. The pintle tip should be manufactured for this test. The objective of this test will be to verify that there is sufficient atomization and impingement and to compare spray angle to our predictions.
  6. Once the combustion chamber arrives, do a cold flow test inside of the full TCA. The objective of this test will be to make sure no leaks occur. 
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