Firiday February 10, 2012
Dear Mr. Fintel,
I thought you might be interested to know that the first test of the paraffin-N2O hybrid rocket motor was a success! You can watch the video on the blog or on youtube at Hybrid Rocket Motor Test 1 However, I do have some concerns that I wish to discuss. The first is that while I got a pressure-time trace for the upstream nitrous Injector pressure, I did not get one for the motor's internal pressure. After firing, I checked that the pressure tap on the forward closure was not plugged with wax. It wasn't. What do you think happened? Might I increase the currently small diameter of the pressure tap? It could also have been an instrumentation error with the sensor itself. Also, It appears that quite a bit of wax was consumed before injection began, causing all of the fuel and also the liner to be completely consumed even with an under-filled nitrous tank (437g). I think I might attempt to thin the walls of the thermoplastic tubing, initiating nitrous flow sooner. I also plan to substantially increase the injector orifice area. I will likely be posting the full report of the firing along with the acquired data under "collected data" later today.
After testing each of four plain paraffins with 2% carbon black as an opacifier, I plan on testing each paraffin with the addition of a polymer in order to achieve a more controlled burn rate. Thanks again for all of your help.
Sincerely,
Sam
I thought you might be interested to know that the first test of the paraffin-N2O hybrid rocket motor was a success! You can watch the video on the blog or on youtube at Hybrid Rocket Motor Test 1 However, I do have some concerns that I wish to discuss. The first is that while I got a pressure-time trace for the upstream nitrous Injector pressure, I did not get one for the motor's internal pressure. After firing, I checked that the pressure tap on the forward closure was not plugged with wax. It wasn't. What do you think happened? Might I increase the currently small diameter of the pressure tap? It could also have been an instrumentation error with the sensor itself. Also, It appears that quite a bit of wax was consumed before injection began, causing all of the fuel and also the liner to be completely consumed even with an under-filled nitrous tank (437g). I think I might attempt to thin the walls of the thermoplastic tubing, initiating nitrous flow sooner. I also plan to substantially increase the injector orifice area. I will likely be posting the full report of the firing along with the acquired data under "collected data" later today.
After testing each of four plain paraffins with 2% carbon black as an opacifier, I plan on testing each paraffin with the addition of a polymer in order to achieve a more controlled burn rate. Thanks again for all of your help.
Sincerely,
Sam
Friday February 10, 2012
Hello Sam,
Congratulations on your successful test!
It was obvious from the video your wax burned/melted much faster than you would have wanted. I know some people have had good results by melting and mixing wax with hot melt glue. That increased the melting point of the fuel and decreased regression rate. I'm not sure what type of wax you used, but there are types of wax with higher melting points that may work better as hybrid fuel, I think one type of wax called hurricane wax has a higher melting point.
I made a hybrid fuel grain many years ago by drawing cut newspaper through melted wax and then wrapping it on a coring rod as it came out of the wax. I never did test that fuel grain but I think it would have worked well. Even a thick cardboard tube soaked in melted wax should give good results.
Keep up the good work and let me know when you update your web site with the test data.
Cheers,
Scott
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