Monday, 6 February 2012

Yesterday I tried out a few modifications to the basic decomposition chamber setup. I added in a proper nozzle/chamber instead of the steel tube I had before, a larger tank made from PVC and a solenoid to control the flow instead of the ball valve and string I was using. The solenoid was also driven by a brand new controll system.  The nozzle was jeft over from the nitrous-ethanol enine which never had a hot Firing.

Despite the actual test being a failure, I got a lot of good experience, and proved the new control system and learnt more about the catlyist. Here is another fairly boring video:

The old control system used xbees to talk to a micro-controller from a computer using serial. I had some concerns about the xbees dropping data so I decided to re-do the system. The microcontroller is now connected to a computer via a USB lan server, which make the computer think the usb device is plugged into it, when it is actually plugged into a remote box (you can have 4 devices plugged in to one box). The great thing about using network for the control is that you can use any computer networking hardware as means of connecting the computer to the usb server. At the moment I am using a wifi bridge, but in the future, for  more critical tasks I plan to use Ethernet or optical for longer distances. The system has been rock solid so far, and it is really cool to controll via computer. The other good thing about using the usb server is that you can plug any webcam into it, and use it to watch the test.

As for the actual test, I am not exactly sure what went wrong. We loaded up the tank, pressurised and left for the control room. Although we briefly tested the system, we did not actually test what the flow rate was, which is something we really need to do, so we dident know how long to pulse for. First I gave it a 50ms burst, and nothing happened. I was getting worried that the solenoid wasn't working, so I immediately gave it a 100ms burst. At that point I could see some steam coming out, so we waited a bit then gave it another 100ms. From that burst the engine gave a decent roar which we could hear inside. After the roar died down I gave it another 2 100ms pulses but after that liquid peroxide started coming out of the engine and for subsequent pulses there was mainly liquid coming out. I waited for a bit, to let any pooled peroxide cook off then tried again, which was slightly better but still allot of liquid. After that I just opened the solenoid to let out the rest of the peroxide.

I am not entirely sure what happened, but I have a few theories. After opening up the engine the catlyist looked much the same as the previous test. There was a bit of fine sand collored powder at the top of the chamber, then whole purple grains. For this test there was a propper injector (just a jet) and also steel wool to spread out the flow, so there must be a different cause for the fine grains.  Anyway so Either the engine just became saturated with peroxide, and couldent handle any more, the catlyist somehow became ineffective or there was just not enough catlyist to decompose the flow of peroxide required to keep the throat happy, or something I haven't thought of (probably a combination of these). We tested the catlyist after taking the engine apart, and it was not verry reactive, but we had flushed quite a but of water through it to clean the system and (being a absorbent material) it was verry wet. I think that the catlyist probally then absorbed enough moisture that either the peroxide came out or was not able to react. I hope that with higher concentration peroxide there will be enough heat that the crystals cant absorb moisture.

I tried putting one grain of catlyist in some peroxide and discovered something interesting. It would start reacting, but then crack or flake into lots of little pieces which would stick to the sides of the container the peroxide was in. You can see some flakes on the side of the measuring cylinder in the photo bellow. I think that the cause of this might be heat stress.  Because the grains are silica crystals it is posible that if they heated up too quickly they might crack. It makes sense that only the first bit of catlyist is cracked because the heat generated decomposing the first bit of peroxide would gently heat up the rest of the peroxide. One solution would be to have some powered permanganate at the injector, although at the moment the cracking is not really an issue. I plan on rapidly heating up some crystals to see if the same thing happens. It is worth giving the clay based catlyist a try, but it might just turn into a big mess.

Really just need to try again with more concentrated peroxide before I make any changes.

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