P18102: RIT Launch Initiative Hybrid Rocket
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Injector Testing

Table of Contents


The injector testing consists of three main phases that are outlined in each subsection below. First, we will begin with a water test as a cheap and safe way to visually note the flow distribution through the series of orifices, as well as measure the mass flow rate. The second phase consists of testing with carbon dioxide, which has a similar vapor pressure to nitrous oxide. This will allow us to perform practice runs for what we want to test with nitrous oxide, but with a cheaper and safer fluid. Once we have an established testing process, we can perform the same test with nitrous oxide. The sections below outline the testing objectives, required sensors, and required equipment.

Testing Objectives

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Additional objectives include:

  1. The actual discharge coefficient of the injector, since theory can only go so far, and this value is most accurate when obtained experimentally.
  2. The performance of the injector and whether or not the experimental design matches with the theoretical design. Validation of design and results.
  3. Whether or not the desired mass flow rate is produced at specified pressure drop.
  4. Whether or not the injector is choked at specified pressure drop.
  5. Atomization of injector spray.
  6. Proper length and validation of pre-combustion chamber length based on atomization.

Required Sensors

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Required Equipment

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Test Setup

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The testing of the injector will involve the use of three substances, H2O, CO2, and N2O.

Test 1 (H2O)

The first test will involve the use of H2O (water). The reason for this is that water is easily accessible, easy to handle, not dangerous, and can be used as initial design validations for the injector. Unlike CO2 and N2O water is a liquid at room temperature, so simulating the injector operating conditions is much simpler. For CO2 and N2O, they must be first be turned into a liquid by applying large pressures, then the discharge side of the injector must be pressurized to chamber conditions in order to simulate the proper pressure drops. For water this is not necessary, and the desired pressure drops can be obtained without having to pressurize the discharge face of the injector.

The water flow test will serve as a way to get a measurement of the discharge coefficient and compare it to the theoretical value to get an idea of how far off the theory is to actual. It will serve as way to determine how well and the repeatability of the manufacturing and results of the injector. The water flow test can also serve as way to measure the uniformity of the flow rates across the injector orifices. All orifices on average must deliver the same flow rate. Uniformity is determined not only by orifice repeatability but also by manifold design and its job in equally distributing fluid across the injector orifices.

Test 1.1

The first initial water flow test will involve the use of one orifice for prove of concept, quick manufacturing, and quick results. The design of the set up is shown below:

The procedure for the set up above is as follow:

  1. Assemble test set up according to assembly drawings
  2. Secure the test set using to clamps. Make sure the fixture is set firmly
  3. Connect the inlet of the fixture to a water reservoir.
  4. Check pressure, flow rate, thermal sensors
  5. Initiate test by slowly opening the valve to let water flow into orifice(s)
  6. If discharging into atmosphere, tune the flow to achieve desired pressure drop.
  7. Record flow rate and pressure drop.
  8. Observe discharging spray for quality of atomization, and length for which it is achieved.
  9. If discharging into a pipe or a fitting, tune flow rate to achieve the desired pressure drop measured by up/down stream pressure sensors.
  10. Perform test 6 times, for 10 seconds each.

Test 1.2

For the second run of water flow test, the full scale injector assembly will be used.

  1. Assemble injector assembly as specified per injector drawings.
  2. Connect the injector assembly to test set
  3. Make sure assembly is secure and firm
  4. Check pressure, flow rate, and temperature sensors
  5. Run an initial flow test of the injector to test performance
  6. Tune flow rate to achieve desired pressure drop. Record values
  7. Stop the flow of water.
  8. Place either a flow rate sensor or pressure sensor in the inner most orifice and the outer most orifice.
  9. Run flow into the injector
  10. Measure the difference in either flow or pressure drop across orifice. The values are to be within 10% difference.
  11. Perform this test for all outer most orifices.
  12. This test will measure the uniformity of the flow through orifices and performance of manifold flow distribution.

Test 2. CO2

  1. Assemble injector assembly as specified per injector drawings.
  2. Assemble CO2 tank assembly as specified per test drawings.
  3. Make sure all valves are closed.
  4. Connect the injector assembly to test set up/CO2 tank.
  5. Make sure assembly is secure and firm.
  6. Check pressure, flow rate, and temperature sensors.
  7. Connect sensors properly to the data acquisition device.
  8. Start test camera to observe injector discharge.
  9. Slightly close the valve downstream of the injector orifice.
  10. Open upstream valves.
  11. Let CO2 run through the test set up.
  12. Monitor chamber pressure until it reaches desired back pressure.
  13. Regulate downstream valve as needed to maintain back pressure.
  14. Maintain test for up to 3 seconds of steady state flow rate.
  15. Close upstream valve.
  16. Open downstream valve.
  17. Take recorded data, and end test.
  18. Take the properties of the fluid measured to calculate theoretical flow rate.
  19. Take the ratio of the flow rate calculated to the flow rate measured. The ratio between these flow rates is the experimental discharge coefficient.
  20. Take the discharge coefficient, recalculate the number of elements needed for injector, and compare with theoretical design.
  21. Take the measured properties during test, and calculate Reynolds and Weber number.
  22. Compare them with theoretical design and atomization criteria.
  23. Observe injector footage to identify proper atomization. Proper atomization is defined by the development of a uniform fine mist from the fluid streams either through impingement or stream instability.
  24. Make design adjustments if needed to meet injector flow rates and atomization requirements.

Test 3. N2O



This was a quick initial test to see if we had the necessary fittings and equipment to perform this test. We used a pressure washer to supply water at an estimated 1900 psi and 1.2 GPM flow rate. This is not the pressure drop or flow rate that we require, but will be addressed in future tests.

Test Video


This was another quick initial test, but this time we aimed to collect pressure data as well as mass flow rate through the single orifice. A DAQ was set up to collect pressure data, however the circuitry was rushed and was not set up properly. We are investigating weather it was something as simple as a sign flip (+ --> - & - --> +) or another more critical error. The raw data is listed below and a post-processed version of will be posted in the future. The mass flow rate was calculated by filling a container with volume markings, while being timed from video data. The video and results of this test will be posted in the near future.

Raw Data 1

Raw Data 2

Raw Data 3