mrcoffee
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Joined: November 2019
Posts: 7
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Post by mrcoffee on Jan 1, 2020 20:03:16 GMT -5
Hi all, Here are the latest round of videos. This is from today: www.youtube.com/watch?v=hlJyU5wKtJEAnd here's some thermal camera footage from yesterday (a longer run where the turbo had a chance to heat soak a bit): www.youtube.com/watch?v=EEZDSTdlElgEven with the safety valve in the propane tank, we seem to be ok on fuel. Currently we adjust throttle with the tank top valve. That goes into a ball valve which we have slightly cracked, which acts as a cutoff valve when necessary. (Plans for an oil pressure controlled fuel cutoff are in the works as well.) I've also attached a couple of pictures that show the sides of our test stand. Please excuse the lack of cable management on the wiring. That will be finalized... eventually.
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hosedup
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Joined: October 2019
Posts: 68
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Post by hosedup on Jan 1, 2020 20:03:24 GMT -5
Ron, yes it is a standard 20 pound propane tank with the OPD type valve. We use the tank valve to regulate flow. It seems to work pretty well. The fuel hose has a ball valve right after the tank fitting. In the beginning, we were not sure how many turns of the tank valve would be needed to operate the engine so the ball valve was added as a quick way to stop fuel flow. In reality, its about a quarter turn to get idle and startup flow and another 1/8 to 1/4 turn to get as high as we have dared to go (20 psi P2).
I have been toying with the idea of having 2 tanks plumbed in tandem feeding a single large needle or vee-ball type valve that feeds the engine. I think this would alleviate any flow restricting safety valves on the tanks. If it wasn't for the difficulty transporting 100 pound propane tanks, I would consider using one of those.
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hosedup
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Joined: October 2019
Posts: 68
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Post by hosedup on Jan 2, 2020 6:45:01 GMT -5
As an FYI, all units on the instrumentation are in PSI and deg C. At one point the EGT / TOT was in F but we changed it to be more uniform with other forum members.
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mrcoffee
New Member
Joined: November 2019
Posts: 7
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Post by mrcoffee on Jan 2, 2020 22:19:26 GMT -5
Hey all, Here's a video from our second run. It incorporates the above thermal footage. Just in case you guys fancied a look. www.youtube.com/watch?v=0V11OxSW5NgThank you once again for all your help and advice along the way. We're far from done, but enjoying every step of the way. -Rhys
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hosedup
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Joined: October 2019
Posts: 68
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Post by hosedup on Jan 4, 2020 18:54:01 GMT -5
Does this look like we are overheating the flame tube? Also, the top plate on the combustor outer housing will glow cherry red in a few places. Mr.Coffee suggests lowering the primary holes and fuel injector. If we go that route, how far? Currently they are at 1 inch from top.
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Post by racket on Jan 5, 2020 0:09:07 GMT -5
Yep , getting a tad hot , your single row of 29 small diameter holes means the air penetration isn't very deep, resulting in combustion very close to the wall , also at only 1 inch displacement from the end there'll be combustion impacting the endcap , but you will have easier ignition from an endcap mounted plug .
The reason I suggested two rows of larger holes was to prevent combustion against the wall , the larger holes will produce deeper penetration of air which should produce combustion across the flametubes cross sectional area , the top row of holes wouldn't have initially contributed to combustion but would have kept the end cap cooler before turning downwards into the combustion zone where the propane was being injected towards the lower hole row.
Cheers John
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Post by finiteparts on Jan 5, 2020 22:51:09 GMT -5
It appears that you are using some form of mild steel for your liner? At elevated temperatures (not necessarily high temps in gas turbine terms), steel will oxidize rapidly and thus you get that reddish oxidation layer. As the temperatures come down, the oxidation will take longer to form, but it can appear just the same. The other thing that happens is the flaking as regions hot corrode away. The flakes can be quite erosive when they go through the turbine. With that being said, it is impossible for me to say if you are running hot or not. The oxidation that we see on the liner could be from excessive temperature or just a time at temperature effect. I would suggest using a stainless steel (like 304 or 321) for your next liner. The chromium that is alloyed in greatly decreases the oxidation rate at elevated temperatures, making your liner last a bit longer. Another benefit of using stainless is that the oxidation color seems to trend better to local metal surface temperatures and thus makes "reading" the liner temp a little more trustworthy. The reason that you are getting hot spots on the top plate is because your combustor design causes the recirculation in the primary zone to scrub the top plate. So you have a high heat transfer on the inner surface of the top plate and basically just natural convection on the outside. I really dislike this type of combustor design because there is a potential to burn through the top plate during operation and have a potential fire situation that could be very unsafe. If it was me, I would weld a dome plate on the combustor liner and have an air gap between the liner and top plate of a 1/2 inch or so to keep the hot gases off of the top plate (read that as structural-pressure vessel). Where the injector passes through the liner dome, I would have a small gap (or better yet, a swirler) to pull air over the cold side of the dome plate (to get some backside cooling) and also to help get air into the PZ. A simple milled slot, radial swirler would be an easy fit for this type of combustor and would greatly enhance the combustor operability. I made a swirl stabilized demo part years ago to show how well a swirl stabilized flame could be anchored in the vortex breakdown bubble. You can see it here: www.youtube.com/watch?v=EMf_ZBZisMEThere was a good cross wind at the time I filmed that and it really was an effective and simple device. If I can find it, I will try to get a picture of the swirler I made from a thick aluminum washer with six or seven slots cut in it with a grinder...super easy. If you just google "radial swirler combustor" there are a few that come up in the images. If you still have questions, I will try to sketch it up. Good luck! Chris
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hosedup
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Joined: October 2019
Posts: 68
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Post by hosedup on Jan 6, 2020 21:30:57 GMT -5
John, Never considered that the large number of small holes would cause low penetration keeping the flame close to the liner. Now that I think about it, that makes sense. I guess in this case less holes but of a larger size are in order. The reason I did so many holes is because when running numbers for hole size, I was looking for a size/quantity config that would yield a nearly whole number. So, at this point, what do you think about 15x 0.305in (7.75mm) giving a surface area 1.1 sq in? Or do you think the holes should be larger? Currently they have a 1 inch offset, I am thinking 2 would be better?
Chris, I really like that swirl flame setup you have. I would love to see some pics and drawings on how its made. As for using stainless, I am 100% in agreement. I am working on sourcing it. I like what you said about putting a dome on the top of the liner. I have some old air tanks that have domes on them I can use. I can weld a nut to the new dome that the injector will thread into and old hole will be modified to make a seal. Same for the spark plug. Can you explain further on how to make the swirler under the dome? A few small holes drilled into the face at an angle?
I need to talk to Mr.Coffee about the radial swirler. I did some searching and it looks promising. Firstly though, the problem with the flame hitting the top plate will be fixed. While fixing it, I plan on welding on a dome as Chris suggested. Once we have a reliable design, we will most likely remake it in stainless.
Anything else glaring that needs to be resolved? Thank you again for all your suggestions.
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Post by racket on Jan 6, 2020 22:54:02 GMT -5
If you intend fitting a cap on the flametube as Chris suggested then you can rearrange holes so that ~1/3rd of the total Primary air comes through the cap via holes/swirler or combo , and the remainder through the side wall.
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Post by finiteparts on Jan 7, 2020 22:24:29 GMT -5
I won't have time to look for the swirler till this weekend. I will try to put up a bit on my Combustor Design post to show how to size the swirler and select the amount or swirl.
As for the "dome"...I was literally meaning a flat plate covering the end of the liner...it doesn't have to be "dome" shaped. Dome is the term that I use for the headend of the combustor (primary zone). I will try to sketch up what I am referring too. I think that it is a simple replacement for the combustor design that uses the top plate to close off the combustor.
- Chris
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Post by racket on Jan 7, 2020 23:07:13 GMT -5
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hosedup
Junior Member
Joined: October 2019
Posts: 68
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Post by hosedup on Jan 9, 2020 9:32:41 GMT -5
Chris, The two images, they very similar. Are they the same engine just at different levels of assembly? They look really nice. I especially like the way the holes have a punched or funnel profile.
I have a few questions:
There is a part that I call a top hat, looks like it's diameter is less than half the main body, right where I assume the fuel (propane?) is injected. Is that the primary set of holes?
I see there are lots of tiny holes all over, is that to help create a boundary layer of air on the combustor walls?
What is your ignition source?
What did you make it out of?
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Post by racket on Jan 9, 2020 16:26:07 GMT -5
Hi They're two different engines , the one with the domed end was on my TV84 based engine jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build whilst the flat lid was on the GT6041 engine jetandturbineowners.proboards.com/thread/78/garrett-gt6041-powered-kart , both were for evaporatative fueling hence the "top hat" for air entry into the vapourising tubes , 4 tubes with the TV84 and 6 tubes with the GT6041. Yeh , the small holes hopefully provide an air blanket at the wall, stainless 304 used for construction. Ignition is an automotive plug/spark mounted in the combustor side wall The TV84 based engine used in my bike had high pressure spray , so a single spray nozzle in a domed head with air swirler and multiple small cooling holes . Cheers John
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hosedup
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Joined: October 2019
Posts: 68
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Post by hosedup on Jan 9, 2020 17:32:49 GMT -5
Very cool. When you used the spark plug in the side wall, how did you seal the plug through the outer housing? I'm trying to work that out on a design right now.
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Post by racket on Jan 9, 2020 18:31:45 GMT -5
Hi
With the plug placement , I weld in the threaded bung to the outer can at a suitable axial position , noting the depth between plug seat and flametube wall to get the correct radial position for the plug seat , then using an old plug with earth removed and the electrode ground to a point , I simply screw into the thread and "centre pop" the flametube wall so that the hole can be drilled in it at the correct alignment
Cheers John
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