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We present our igniter, the device that starts the combustion reaction in our cryogenic motor. This small piece of hardware is actually a mini-rocket on its own as it combusts hydrogen and oxygen to produce a hot flame to ignite the propellant mixture in the combustion chamber! 🔥❄️
As is customary during study week, pre-semester 1 exams, I find myself getting distracted by rockets. With winter coming out in full force, the garage is not so enticing so I found some computer work I could do for my spark torch igniter. I am gearing up to test it again soon (I finally have some time) and thought I would sort out my data analysis spreadsheet.
The igniter GUI will log all the data to a CSV file from which I can post process. To make this even easier I wrote a MATLAB script to import the data, graph it, display the performance specifications and resave all this new information and graphs into the second sheet of the raw data file. Thus having the whole test info in one place.
While doing this, I found a mathematical error in one of my post processing equations which in turn gave some pretty good performance specifications (I left the π out of the orifice area calculation!). The old data was within reason and hence is why I never thought to double check, it did not help I was gearing up to leave town for the summer after the last test as well. If I had analysed the video better I may also have picked up on this.
Now fixed, the corrected test data was as follows,
|Fuel mass flow rate||0.022918||kg/s|
|Oxygen mass flow rate||0.009416||kg/s|
The flow rates are well and truly off the total expected, of 0.0099kg/s, whereas the mixture ratio was correct but from the video, it looked very oxygen-rich, not sure about this. The chamber pressure was also about 15 PSI higher than what it should have been. I am going to essentially write this test off, as discussed earlier I now have some pretty accurate orifices and have verified these with water testing. Along with this improvement, I will also remove the swirl injection of the fuel and run the optimum mixture ratio for the propellant, and hopefully, then I will be in the ballpark of the calculated specs.
This update is pretty late, as this occurred at the end of November 2017, before I headed out of town for my summer internship. I have not been able to do any testing since but am just now revisiting the igniter as I am back in town and at University again.
After my first initial hot fire semi-success I was on a good high and happy everything worked. In order to show some friends how cool this was, I set up in the exact same manner as before and attempted another hot fire, this time I was unable to light the igniter.
The inlet pressures and valve timing were all exactly the same, the only difference I noted was the spark plug had eroded, this was replaced and tried again. No ignition.
After talking to others over the summer I have a rough idea on how to proceed,
- Switch from swirl fuel injection to 90deg with ox
- 3D print (with SLS) smaller and more precise orifices that will press fit in my 1/8 nipple fittings
- Future version, move inlets further away from spark plug to help prevent erosion or lengthen hole so does not protrude into chamber as much
I’ll start with the orifice fix and go from there. One other thing is that for each test I need to hire an O2 and N2 bottle which is a bit costly for me as a poor student, I am seriously thinking switching fuels from Ethanol to a gas like methane for example. This would alleviate the N2 and only require buying a mini disposable gas canister from the hardware store. Thus enabling me to test more often and gain experience much quicker.
I also have borrowed a NI Labview DAQ module, so I will also work my way towards converting the avionic system over to this. Labview for students here I come!
Seems I have not been the only one burning out spark plugs and having failed ignition! (My last series of testing was a headbanger because of this!)
Video Caption: A student society that builds a record-breaking hybrid rocket engine powerful enough to lift an SUV? The Cryogenic Propulsion Team recently tested their spark torch igniter for the second time. Watch the video to check it out!
Over the last year I have been working on a 3D printed spark torch igniter, this has been a little side project while at university and eventually the experience gained will lead to this or a similar igniter used to light the main chamber of my rocket engine.
Yesterday I achieved the first hot fire tests of the igniter, the final test is shown below.
I ran through three hot fire tests, tuning it a bit each go. As can be seen, it is currently running oxygen-rich whereas it was designed to run fuel rich, the flame is too blue.
The design chamber pressure is 70 PSI, in this test it is ~85 PSI, so still some tuning of the inlet pressures required.
Before this test I had to replace a solenoid with another I had that has a smaller orifice than the fuel orifice on the igniter, although there is only 0.1mm difference this could slightly affect the performance. In the future, I will implement different sized orifice fittings to help fine tune it as I am not 100% on the size of the 3D printed orifices in the chamber.