Sunday, 26 February 2012

Yesterday I finished off the new test system, consisting of a test stand with pressure transducer and load cell, and fill cart with quick disconnect. Here are a few photos:

The system is reletevely simple but cuts down on the amount of peroxide handling and will reduce the risk considerably. I have discussed the system previously, but basically the manifold on the cart controll the 3 steps required to fill the stand tank. Firstly the vacuum valve is open (while the other 2 are closed) and the vacuum pump turned on drawing a vacuum in the system. Once at about -80KPa the pump is turned off and the valve shut. The fill valve is then opened sucking liquid into the sytem which makes its way into the tank. when there is no more liquid it sucks air which serves to suck the remaining liquid in the line into the tank. Once the syustem is at atmospheric pressure the fill valve is closed and the presure valve (the needle one) is opened filling it to the pressure set by the regulator. There is also a relief valve on test stand which will prevent overpresurisation .

I practised filling and dumping distilled water through the system quite a few times, and although I quite happy with its performance, there were a few issues. Firstly it is impossible to disconnect the quick disconnect over about 200PSI, which makes it useless. It makes sense that you cant disconnect it under pressure, but I thought I might be able to force it doesn't budge. I need to look for a better one, perhaps sometihng designed for hydraulics. Secondly I am concerned about the amount of liquid left in the run tank after it is completely emptied. I measured it by tanking the valve off the tank and found it to be 200ml. Afterwards I found out that nitrous tanks are designed to be run on an incline, whoever I am not sure how you know which way to angle it, as you cant see where the syphon is inside the tank. The next door neibour at the workshop suggested marking where it is when you put it in the tank and measuring the number of rotations. I suppose I can handle loosing 200ml each test but I would prefer not to. It wouldn't be so bad if I was running a few tests. Lastly I am not so happy with the time taken for smooth flow to start when opening the run solenoid after a fresh fill. There is quite a but of air and water which comes out in pulses and it takes about 3 seconds to settle down to smooth flow. There also must be a fairly large pressure drop across the solenoid and check valve because even at 800PSI the water coming out seems a bit gentle. I think the check valve might be restricting the flow which makes it look weak with water, but the flow rate of peroxide will be much less os it should be alright.

We also mounted the new test stand on a proper concrete slab which was already in the car park for the workshop. There are female anchors there now so we will be testing out there from now on. The small area we did previous tests at suited us before but all the grass and confined space make me nervous for tests with more concentrated peroxide. Hopefully I can give the new test stand a go this week sometime. I still haven't got the electronics going yet. After the its time to start working on a flight engine!

I have been giving some thought to switching to using lab view for controll and data logging. Ever since using robolab as a kid I have disliked graphical programming languages but after doing some research into just how powerful it is and how manny people use it I am nearly convinced. The icing on the cake was when I found out that you can use a arduino instead of their expensive DAQ's. I have always prefered the DIY aproach as I think you learn more that way, but you need to decide what you really want to accomplish and focus on that.

We also concentrated a batch of peroxide yesterday. I got a neibour at the workshop to make up a large stainless steel tank so I can concentrate more peroxide at a time(at the moment I am using a bowl), but unfortunately iy wasn't finished so we only have a few letires for this week. I have also invested in two really good respirators for use around the peroxide. I haven been able to find anything saying that the peroxide vapour is bad for you (in low concentrations) but the vapour has been concerning me and I thought it was a good precaution to take.

Monday, 20 February 2012

On Sunday we repeated the test (%75 with zeolite catlyist) which we had a leaky o-ring last attempt and there was a huge difference in perofrmance. I dont really like spectators but my parents wanted to see the new workshop and I said they could stay for the test.

After two warm up pulses I gave the engine a two second run during which we couldn't see any activity from the nozzle although the nearby grass was being ripped to pieces. It took me a few seconds to realise what was going on, but then I realised that the exhaust was completely superheated gas. We probally ran it for about 12 seconds   in total in 2-5 second bursts before the small tank ran out. towards the end fire stared coming out of the nozzle which looked quite spectacular and I was worrying that the nozzle was melting but we later discovered that it was the steel wool. The exhaust started getting a bit clowdy towards the end meaning the catlyist was loosing activity but we refilled the tank for another test without changing it to see how long it could last. The next run was cloudy for one quick burst then liquid started coming out. I still have no idea how much thrust it made but it was definitely loud. It is clear that we are going to have to optimise our pack design. I think larger pieces of zeolite with a more uniform shape will help, as there is more than enough catlyist but it is getting blown out too fast. I recorded the test in high speed @ 440FPS so although it was only recording for about 5 minutes, the video is about an hour long and I dont ahve any time to edit it. Its quite booring anyway but if people really want to see it I would be happy to edit out the good bits.

We have have also been working on the new test setup. I had ordered just enough teflon line fittings to make 4 hoses, (which is how many we need) thinking it would be east to make the hoses up. As it turns out making the hoses is a delicate art and I have managed to mess up two of the three I have attempted. The first one leaked because the Teflon end was not square, and the steel braid on the second one caught on the fitting so it twisted when tightening. Because it would take a few weeks to net new fittings from overseas I just ordered 4 pre made hoses from inside Australia. They were quite expensive, but I really want to have the new setup mechanically finished by this weekend. Next time I order hose fittings I will be ordering more than I need. I have also been searching for a suitable quick disconnect for some time and came across a "brake quick disconnect" in a auto-parts suppliers catolog. I need a fitting that seals on both end to prevent getting covered in peroxide when disconnecting it. It is apparently "lossless" which one would hopee it would be if using it on their car brakes. It has teflon seals and is rated to 2000PSI.... Perfect!

Wednesday, 15 February 2012

Yesterday we did a test with a similar set-up as Saturday, but with two variations. I double coated the catlyist, by adding more permanganate solution to it and this time we used more concentrated peroxide of about %75 concentration. Despite a leaky o-ring which is apparent in the video, the test was quite successful and quite a bit louder than the %50 peroxide had been. It was so loud that I had to cover my ears for the longer runs. Unfortunately we lost quite a bit of peroxide to the leak so we dident get very much run time. We were considering fixing the leak and testing the used catlyist with more peroxide but it was late so we decided to pack up. We had had several problems getting the test going, with electrical issues and a blocked injector which meant we had to take apart the engine. We haven't inspected what caused the blockage yet, but I believe it will be a bit of rust from the steel line. We decided to ditch the injector to avoid any more blockages. I think that this contributed to the pressure oscillation which can be heard in the engine and seen in the stream of peroxide squirting out of the injector assembly. I was happy with how the catlyist performed, but it when inspecting the engine after the test we noticed that the pack had become quite compacted and was now about 3/4 of its original height, and there was quite allot of powder at the bottom. We reallyneed to start trying different ways of packing the catlyist to avoid this problem, and the large pressure drop which results. Some of the guys on Saturday suggested layers of mesh, and this is worth a try, but also having some way of raising the catlyist up in the chamber would be good to allow the engine to build up pressure and give space for any un-catlyised peroxide to mix and decompose. I would also like to eventually be able to package the catlyist so they are mroe easily able to be changed. We might do one more test with spacers with the current setup, but what we reanny need is more feed pressure, so we are now focusing on the new test stand and other hardware.

Monday, 13 February 2012

Yesterday a few of the guys from Lunar Numbat and some other friends came over for a meeting about where Australian Rocketry is going. We didn't get the turn out we were hoping, so we didn't have the meeting but I fired up the engine to show the people that came.

The setup was the same as the last test, but this time I used a different type of catalyst which I heard about from a chap at ASLI. It is a zeolite, which is a type of mineral usually used for absorbing oil spills etc. The idea is that it would handle the heat better than the silica gel. There was a huge difference, and this time all of the exhaust seemed to be turn to vapour. I was quite happy with the results, I just hope that the catalyst will perform as well with higher concentrations. The reason for the wagging of the exhaust at the beginning is that the converging part of the nozzle is partially blocked with steel wool (Ashley came up with that one). I need to make a small spacer to raise the bottom of the pack up to fix this. Interestingly after the feed pressure was increased to 110PSI the problem went mostly away, although the exhaust was still quite rough. I ran quite a bit of peroxide through the engine , and it didn't show any loss in performance. Interestingly after stopping the engine for about 20 minutes while we refilled the tank the catalyst seemed to stop working. After the test we all took the engine apart and did some brainstorming about why this happened, everyone came up with so manny great theories (too manny to discuss) and it was good fun to discuss the problem with others. Thanks to trent for his help assembling the engine.

The next step is to test the engine with higher concentration peroxide. I am currently concentrating a batch which I hope to test later tonight or tomorrow if it keeps raining. On friday I got all the parts I had been waiting on, so I have been starting to assemble the new test stand a fill cart. I have decided on a armadillo style vacuum filling method. I have been so far testing the catalyst test setup with compressed air at 110PSI, because the PVC pipe used as a tank is not rated for high pressure. With %50 this works well, but I am afraid that the chamber pressure with higher concentrations will be too high. I know that ideally the flow should regulate itself to allow an amount of peroxide in to maintain the chamber pressure, but I think that the check valve will cause the flow to pulsate too much. By that I mean that that too much peroxide will get injected raising the chamber pressure above the feed, which will cause the check valve to kick in and stop any more flow, causing the cycle to repeat.

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.

Thursday, 2 February 2012

I had been getting a fit frustrated with the slow progress (have been waiting 2 weeks for parts) I have been making with the new test stand so I decided to make a simple thruster to test the silica gel consumable permanganate catalyst I want to use in the 100N engines for the hovering platform. It is pretty simple,  just consists of a vertical pipe which is filled with peroxide, and pressured with compressed air from a fitting at the top. There is a relief valve in the top also for if the peroxide in the pipe started decomposing. There is then just a right angle, check and ball valve then a shorter length of pipe where the catlyist is. I made a crude nozzle out of a hole in a end cap. All the fittings are brass or gal, which is not ideal but the peroxide is only there for a short period of time.

 I really enjoyed building it, I just sat down in the hardware store and went through a few design revisions. the first design I put together was made all of PVC pipe and fittings, which I figured would be good for peroxide compatability.  Since I was only planing on using it for low concentration peroxide I thought the PVC probably wouldn't melt. The PVC ball valve was quite stiff and would have been hard to trigger remotely (just by pulling a piece of string) so I went with a brass ball valve which was much smoother. Eventually I also decided to go with all metal fittings so I could use it with higher concentrations of peroxide (without it melting). I really enjoyed just sitting in the hardware store trying to figure out the most efficient way to make the thing, it was like building something out of lego... The whole thing ended up being about $100, although I think I was undercharged a bit. Most of the cost was in the relief and check valve, which were both designed for hot water systems, but siuted my application exactly. I was debating weather to  bother having a relief and check valve in such a small thing, but I decided to head caution.

The thruster worked really well and I learnt allot about the silica catylist. I was quite surprised that the exhaust appeared to be all gas even with cold %55 peroxide. The catalyst tube just consisted of  granular catlyist with steel wool at the end to stop it getting blown out. The first time I fired it by opening the ball valve all the peroxide just squirted out covering everything. The nozzle hole was too big, and the peroxide flowed through the catalyst too quickly to react. For the first run the peroxide was also about %55 and was chilled as it had been in the fridge. We obviously triggered it remotely (with string), and watched it via camera. One thing I had not thought of till now was how to clean up if things get covered in peroxide. I ended up just hosing the set-up down, which worked because there were not any electronics, but I am not sure what I would have done if there were. Will have to give that one more thought. For the first run the catlyist tube was about half full, but for the second run I changed the catlyist and filled it all the way.

For a second run I changed the nozzle for another with a smaller hole, and instead of triggering it by pressurising then opening the valve, I opened the valve first then slowly increased the pressure. It worked beautifully and there was a nice jet of steam. For the second run the peroxide had also warmed up. I also put more peroxide (about 200ml) in this time.

I emptied the catlyist pack to see what condition it was in and this is what it looked like - second test closest, third farthest and some new catlyist on the paper.:

The first 2cm had turned into a fine white powder, but the rest of the catlyist looked pretty good. I think that the reason the first bit of the pack turned to powder is because the peroxide hits it at high speed which causes it to rub with the other unrestrained grains, pulverising them. The next time I do a test I plan on putting some steel wool at the beginning of the pack to compress it and diffuse the incoming stream. I was quite impressed that apart from the powder there was not much stripping of the catalyst, epically with such a long skinny tube, in which the flow of gas would be quite high, and considering that the thing ran for about two minutes. I am keen to see how it holds up to %90.

I did a third test in which I reduced the nozzle again and experimented with pulsing the flow, whihc workd quite well. I pressurised at 60PSI but I think that because there was no much line between the compressor and the the tank the pressure increased too slowly. There was quite a delay between when I would open the air valve and I would see a result. Here is a fairly uneventfully video of the third test. You can see the result from pulsing the pressure.

We found a really nice area out the back of the shed with is mostly protected on its sides by bessa brick. I plan on clearing the grass and laying bricks when I have some free time.

I plan on concentrating some peroxide to %85 this weekend and repeat the experiment. I would also like to add in a solenoid because the ball valve is a pain to operate with a string. I also realised that I need to give more thought to test logistics with peroxide because although I at no point felt unsafe (was wearing full PPE) there were times when I thought I could have done things better.