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 holes). Run nitrous through the system with a pressure equal to the pressure drop (the nitrous will be emptying into ambient pressure). Use the depletion time of the nitrous to calcluate a mass flow rate. Compare that mass flow rate to the predicted NHNE mass flow rate. Adjust your Cd accordingly in the NHNE model. Then, delete/add orifices to the center body until the NHNE model achieves the desired mass flow rate. After that, run a test again and see if the mass flow rate matches the model with the new Cd. Iterate like this until the mass flows closely match.
    1. For example, say we test our center body and the mass flow is too low. We would then modify the Cd of our Dyer model until the predicted mass flow closely resembles the actual mass flow. Since that mass flow is too low, we would then add another orifice (or two) to get the mass flow back up to our requirement. We would then test a new center body with the extra orifice, and see if the mass flows match. If they closely match, we're good to go. If they don't, then we have to keep iterating until we get a good mass flow. 
    2. If the mass flow is too high, we would modify the Cd of our Dyer model until our predicted mass flow is also higher than our requirement. Then, we would delete an orifice (or two) to get our Dyer massflow back down to the requirement. Then, we would make another center body with one less orifice and see if the mass flows match.  If they closely match, we're good to go. If they don't, then we have to keep iterating until we get a good mass flow. 
    3. This is nice because we can enforce the same mixture ratio by changing the number of orifices on the pintle. So, if we initially get massflows that are higher or lower than what we wanted, we don't have to change annular gap dimensions.
  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. Since we are currently utilizing a small annular gap (6 thou) due to small mass flow rates, we expect the annular sheet to be sufficiently laminar, but we will verify this during testing with cameras. 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 nitrous. We know the amount of water we're running through the system, so if we time the test, we will know the mass flow rate. If that mass flow rate is higher than what we expected, we will adjust Cd until our model matches that higher mass flow rate, and then modify the annular gap accordingly. If our mass flow rate is too low, we will adjust our Cd until our model matches that lower mass flow rate, and then modify the annular gap accordingly. We will run a test again for either case to see if the mass flows now match. However, since our annulus is very small, we don't have much room to make it smaller if the mass flow is too high. Therefore, if the mass flow is too high, we will let our mixture ratio drop slightly and keep our annular gap the same. Also – just thought of this – we could change the number of film cooling holes, although this means we would need to remake our baseplate with more holes, so probably not a good option. 
  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 controllers by performing multiple single fluid cold-flow tests and actuating the ball valves to various degrees. For the nitrous, 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 nitrous 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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