Propulsion Cold Flow Update - Plumbing

Written on10/27/2020

Cold Flow Test & Propulsion Team Update

Hey readers!

It’s been a while since we’ve posted about the state of our propulsion team and it’s about time we give a little update. 

Since the start of quarantine, the propulsion team has been hard at work preparing for the cold flow test. Essentially, a cold flow test tests the insides of our propulsion system - namely the piping, valves, and engine (injector, chamber, nozzle) - by replacing the propellant with water and pressurizing the system. We first do an individual cold flow test on each tower and then do a final cold flow test with both towers integrated into one final system. The first two cold flow tests have particular emphasis on the valves and piping system, so we focus a lot on making sure our piping layout is exactly how we want it and making sure we can collect data accurately and knowing what to do in the event of a failure.

Not only does the cold flow test of each tower make sure all our valves and piping are working properly, but we also get extremely valuable pressure drop data, which will help us determine more about our system and the final exit pressure of our propellants.

What are all the parts that go into a cold flow test?

Our first cold flow test was conducted on October 6th, which tested the ethanol tower. Ethanol (C2H5OH) is our fuel and Nitrous Oxide (N2O) is our oxidizer. Doing the ethanol tower first is a lot easier compared to starting off with the nitrous tower since we could replace the ethanol with water and pressurize it with a nitrogen (N2) tank. Nitrous oxide, however, is significantly more dangerous and takes quite a bit more safety precautions to handle.

To start off, we needed to develop a piping layout with different valves and create a pressurization system. We created a P&ID (Piping and Instrumentation Diagram) that outlines all of the valves and tanks in our system. To draw the P&ID, we used a simple application called draw.io and created a legend to indicate the different valves. Perhaps in a future blog post we’ll go more into detail about each valve and their significance in our piping system. For now, we’ll give a quick rundown of what the system depicts, starting from the N2 K-Bottle and working our way down to the injector.

The N2 K-bottle is a large tank that serves as the pressurizer for the water in the cold flow (which will eventually be ethanol in the static fire test). We have a pressure gauge and thermocouple, which reads temperature, immediately after the K-bottle so we can make sure the pressure and temperature of the N2 are where we want them to be before letting the N2 into the rest of our system. A solenoid valve follows which will open if the pressure and temperature readings are correct, preventing the need for people to manually open the valve. However, the solenoid valve (NCSV-1) didn’t arrive for our ethanol cold flow test, so we instead used a manual ball valve and pulled a string far away to open the ball valve.

After the manual ball valve, we have a branch for a thermocouple and pressure transducer as well as a branch for 3 different pressure relief methods. This way we can vent the N2 to the ambient atmosphere in case the pressure gets too high or if we need to abort the system.

This then connects to the ethanol (C2H5OH) tank which houses water during the cold flow. Since the N2 is pressurized, it pushes the water down to the NCSV-3 solenoid valve with the desired force. There is also a branch for a pressure transducer and thermocouple and a branch for a manual fuel drain where we can expel water out of our system in case of a failure or need to abort the mission.

Once we actuate the solenoid valve NCSV-3, The water is sent to the injector and sprayed out into the open air. For our cold flow test, we did not yet have the resources to machine our injector and chamber, so we instead 3d printed our injector design.

Next week we’ll do a part 2 cold flow update with injector and chamber design.

Thanks for reading this far!


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