Yesterday we conducted three tests with the new set-up. The tests were as follows:
- %50 Peroxide
- Permanganate Zeolite caltyist filling the entire chamber with only steel wool after the injector and at the exit
- Recording Pressure but not thrust
- 430PSI feed Pressure
- 75 ish percent (we didnt get the density unfortunatelly)
- Same catlyist set-up as 1
- Recording Pressure + Thrust
- 610 Feed Pressure
- Same concentration
- Half caltyist half wax fuel grain
- Recording Pressure + Thrust
Here is a video of all 3 tests combined:
The first test was really just to test out the new system and get some data to compare with that from the more concentrated peroxide. Buren didn't want to put the loadcell on for the first run in-case the engine "exploded" and broke the load cell. I tried to explain that in the event that it did "explode" we would have bigger issues than a damaged loadcell, but I wasn't in the mood for arguing so we left it off for the first run.
The first run was pretty much the same in terms of what the exhaust looked like. It might have been a bit louder, which could be explained by the increase in pressure. It was extremely loud at the begining but got quieter about 4 seconds into the test. I thought this might be because of the catlyist becoming less active, but it stayed at about the same volume for the rest of the test, which made me think it might be something else. The spent catlyist looked like it had some life left in it.
The second run was louder and produced less visible steam, and you can see the engine shaking in its mount. Looking at the high speed I think that there might be some resonance with the cantilever load cell. Towards the end the exhaust did start becoming cloudy, and the vibrations stopped. I was a bit disappointed that the exhaust was not completely clear like it was during the last test of the old test stand, but that might be because the peroxide was not quite as concentrated.We used a different batch of catlyist for the second and third test and it had a permanganate coating on its outside which quickly washed away at the beginning of the test in a cloud of purple. The spent catlyist looked almost completely as it had before being coated/covered with permanganate. I think that the only reason the engine kept going is because the catlyist material was hot.
For the third test we decided to have a bit of fun and try out a hybrid. We cast the chamber half full of paraffin wax (with a hollow core) and out on o-ring on top to support the steel wool and catlyist. Unfortunately we didn't get any combustion but it did make for an interesting test. It started out the same as the others, but started spluttering and for a while there was verry little exhaust. About 30 seconds in there was a loud pop and then the engine continued as normal. What happened was the wax and catlyist which was not properly supported clogged the nozzle. I think that eventually the wax must have melted and the blockage cleared. When we took apart the engine we found that most of the catlyist was gone. It was interesting to note that after the blockage cleared the exhaust looked much cleaner than it had in the previous tests. I am not entirely surprised we didn't get any flames, from what I have read it is difficult to get reliable ignition with any less than 80ish percent. I think that this is because there was not a post combustion chamber with a convergence, not just the divergence which was there because the steel wool blocked the convergence in previous tests. We had been meaning to conduct another test with a spacer to create a post chamber but the lathe still isn't working and I haven't been able to find any pipe which is the right size. I am confident the wiggle in the exhaust will go away with a post chamber.
We still dont have any propper injector in the chamber, just a hole. It is posible that there is just too much peroxide flowing through it (similar to the first few tests) and the catlyist cant decompose it.
Unfortunately the logs of pressure and force were recorded in a labview format and I haven't had time to figure out how to convert it yet. I can sort of play back the data, but I cant plot it. From what I can see the data is not very good. The only log where I get anything resembling a decent plot for pressure was for the last test, and only when the exit was blocked. The thrust was even worse. I still haven't calibrated either sensor, so I am just looking at them as volts. I am not sure why the results were so bad. I set the gain on the load cell amplifier so that it maxed out as hard as I could push it and there was definitely a period of time when there was half that amount of thrust. Further investigation required. We need to test the sensors more throughly.
I am quite happy with the new plumbing system. Filling was extremely easy, posibly a little too easy as I nearly left the fill valve open from the last test while using the vacuum pump. We really need to have a checklist with an extra person to make sure the operator doesn't forget anything. Startup was sharp and I dident notice any pulsations from gas in the lines at startup which was good.
It is clear that the catlyist needs significant improvement before it can be used for any decent duration I intend on trying a few new materials and it is still early days because there were a number of things that could explain the not so good performance of the second run, but it might not be possible to run for long durations using it. If we cant get it working well enough for a decent hover (10 seconds is about my minimum) we will have to look at alternatives. A liquid catlyist is one but I don't like the sound of a second set of plumbing, especially for the small hovering vehicle like we want to build. One alternative is a compact hybrid (small L/D) with a small consumable catlyist pack for ignition. In addition to sustaining combustion a hybrid would also raise ISP. The downside would be that it would be much hotter an would require some sort of cooling.