3D Printed Igniter Testing Round 2!

I got around to testing my 3D printed spark torch igniter again and this time with great success.

To give some background leading up to this test period, the igniter was printed with the intention of using the orifices within the body itself for propellant injection, the fuel was set up to swirl and the oxygen straight in. If you saw my first tests, this did not work so well. Since then I fitted precision orifices within the fitting that screws onto the igniter, drilled out the oxygen orifice within the igniter body and plugged and redrilled the fuel orifice in the body, so now the propellants impinge at 90° to each other.

I carried out 14 tests as shown in the video above, varying the inlet pressures of the oxygen and fuel, trying to achieve the most optimum performance. Of note, I tested with a methanol/water mixture (75/25%) instead of ethanol, as I was at a different test location and only had access to methanol. With that in mind, the testing was tuned towards this fuel mixture.
All tests used a 1mm orifice on the oxygen side and a 0.35mm orifice on the fuel side.

I aimed for a mixture ratio of 1.279, tests 11 and 12 came closest to this and as can be seen the plume looks pretty nice. You can see the earlier tests are oxygen rich and the later tests become more fuel rich. The design chamber pressure is 70 psi, but as can be seen I only ever really achieved mid-30s (avg). I put this down to the lower overall mass flow rate with the new orifices and hence the larger than needed throat area now.  I had previously burnt through a few spark plugs (I use an NGK ME-8) and had purchased a few more just in case, but this was not meant to be with no burning of the plug in all tests.

For all the tests I had to deal with a dodgy oxygen inlet sensor, I had not had any previous trouble with this before but all of a sudden it would read between 10-20psi out for each test. This meant I had to change the offset in the code to achieve a zero starting value, because of this I think there would be a fair bit of error in the ox inlet pressure readings. I am using cheap pressure sensors so only have myself to blame, they are a bit noisy but have been working good enough for this project up until now.

I tested again the following day with mixed results. I set up as I had for test 11, 170psi on the ox side and 220psi on the fuel side, upon ignition it was clear that not all the propellants had combusted. Mach diamonds were still visible in the exhaust but propellant still also came out. I then tried upping the feed pressures on both sides to try and increase the combustion pressure but this did not work too well and I started to reach the limit of my oxygen regulator. I then reverted back to a 180psi fuel feed and 160psi ox feed, and the igniter ran as good as it had done the previous day. 

In all, I had 26 successful test fires of the igniter, where a mixture ratio of ~1.3 ended up being a good fit. I really need to run the tests with ethanol, but I imagine there would not be too much change. I’ll probably keep tinkering and if time permits print a new version to achieve my design chamber pressure, but as it is in its current state, I would be happy to bolt it onto my main chamber.

Where too next?
The hireage of oxygen and nitrogen really kills it for me on this project. What I would ideally like to do for the next iteration is switch the fuel to LPG, this I can steal from my BBQ bottle, is super cheap, self-pressurizing and is always around the home. This would eliminate one cylinder of gas at least and make it easier on my pocket. The whole point of a spark torch igniter is to bleed off some propellant for the main engine, so am I going to build a LOX/LPG rocket, no. But as I am just playing around I do have a few ideas for this little rocket propellant combination.

Spark Torch Igniter Update: A look back at some data

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
mixture ratio 0.410846
c* 394.4801 m/s
c 515.1133 m/s
cf 1.305803
ISP 52.509 s
Thrust 16.65591 N

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.

For more igniter updates and background, check out the page here.

3D Printed Igniter Test

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.

You can read more about the project here.

Monash Aerospike

This deserved a post on its own.
I found a couple more video’s of this 3D printed aerospike online which go into a bit more detail.

Of note, the engine has multiple internal chambers, which in the future could be used for thrust vector control, as well as the regen cooled chamber, the spike is also cooled. The engine burns Methane and Gaseous Oxygen producing a thrust of 4kN or 1000lbf, the video below shows a burn time of 60sec.

More info on the project can be found here and here.

WARR Rocketry 3D Prints Hybrid Mold

WARR, students from TU Munich have been hard at work continuing their hybrid propulsion work and experimentation. With the latest fuel grain being assisted by 3D printing the shape and then pouring the HTPB in, thus avoiding any demolding issues that may arise as it is all burnt as one.

I know RML Spacelab have used this technique, taking it as far as getting individuals at home with a 3D printer to print and send in the mold parts required. A great way to contribute to a project.

I look forward to seeing this engine fire, it should be spectacular!

SEDS UCSD Prints, Tests Thruster For NASA Cube Quest Competition

SEDS UCSD’s Callan thruster (Credit: SEDS UCSD)

UC San Diego, CA – UC San Diego’s Students for the Exploration and Development of Space (SEDS UCSD) tested its first monopropellant thruster, Callan, earlier this summer at Purdue University to confirm its designed thrust of 1 lbf at ideal steady state operation.  The thruster is part of the group’s NASA Cube Quest entry, Triteia, and aims to propel the cube satellite into lunar orbit.

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Vulcan-1 Pictures

Vulcan-1 Launch (Credit: Bryan Dierking)

SEDS at UCSD member Bryan Dierking has an extensive photo collection of the teams Vulcan-1 rocket build and launch, from conceptual sketches to the unfortunate aftermath it is worth going through the album and having a look.

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