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.

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