jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 19, 2018 19:13:00 GMT -5
Not too much progress tonight but I got the charge pipe welded up and a silicone boot on order
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Post by racket on Jul 19, 2018 19:46:18 GMT -5
Mmmmm..........it might need to be a tad more aerodynamic , the air is moving pretty quick , there'll be a lotta turbulence at that "corner" , turbulence means losses , losses mean less power output from the engine .
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 19, 2018 19:50:44 GMT -5
Would something like this be better?
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Post by racket on Jul 19, 2018 20:09:19 GMT -5
Yep , the larger the bends radius the better , but sometimes if space is limited then an increase in diameter will help keep airspeeds, and losses down, if a tighter radius is used. .
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pcbindex
New Member
Joined: July 2018
Posts: 1
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Post by pcbindex on Jul 22, 2018 22:43:41 GMT -5
The everlasting theme in PCB’s manufacturing: environmental protection and
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 24, 2018 20:34:16 GMT -5
I had the day off today so I made a crude little test stand for the engine. The rubber boot and mandrel bend showed up today but the diameter was too small so time to wait for a new one. I welded a bracket to my flange spacer And 3d printed a front support. It would probably melt in actual service so I'll cnc one from aluminum eventually.
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 24, 2018 20:41:34 GMT -5
I got an electric power steering pump from a mazda 3 for my high pressure fuel pump. I gutted out all the control electronics and I'm waiting for an electronic speed controller to direct drive the brushless DC motor and control the speed for throttling.
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 26, 2018 21:45:00 GMT -5
My new mandrel bend came from Summit today. That was super fast international shipping for only $10! Don't worry I'll cut it a little shorter before I weld it all up. I'm thinking I'll put it in the lower third of the combustor. I also got the bungs welded in, now just waiting for some fuel plumbing, nozzles and a spark module I've got my power steering (fuel) pump converted to run off an Arduino and I can control the speed through the serial monitor on my laptop but I'm still working on controlling it with a pot so I can use a knob or e-bike throttle
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 30, 2018 21:48:40 GMT -5
The CNC is chewing away at my front support I got the charge pipe fitted up It's much smoother than the fabricated one! A nice tight fit before welding
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Post by stoffe64 on Jul 31, 2018 3:10:10 GMT -5
It should be straight in,preferably with a diffusing funnel closest to the outer combustor casing not the way you did because you get a big swirling of the air insider the outer combustor casing. Cheers/Stephan
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jeffreyguy
Junior Member
Joined: June 2018
Posts: 51
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Post by jeffreyguy on Jul 31, 2018 8:40:37 GMT -5
I did it that way because it presents more outlet area but I should've checked into any negative effects before I cut the hole. I have seen other builds do it this way but if it hurts effiency Ill fill the hole and move it. would straightening vanes help with the current setup?
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Post by racket on Jul 31, 2018 17:31:26 GMT -5
It certainly helps with outflow area , but the swirl going around the flametube and creating a helix flow means more distance covered and more frictional losses, then the matter of "free vortex" which requires a pressure drop and another velocity increase as the air spirals into the flametube, in a worst case scenario we've seen very poor mixing of fuel and air within the flametube .
When copying other engine designs , make sure they're good designs with a proven performance , theres been a lot of "tangential" delivery tube builds so understandable why they're copied , but its not the best way to do things , swirl is beneficial in the Primary Zone , but best accomplished by swirl producers in the Primary Zone , the rest of the flametube doesn't need it .
The addition of a diffusing "funnel" at the end of the delivery tube is the best way of increasing flow area at that point and allows the air to spread out around the flametube
Cheers John
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Post by turboron on Jul 31, 2018 20:03:18 GMT -5
jefferyguy, the Allison Model 250 Outer Combustion Case is a good example. It has two air delivery tubes from the compressor that diffuse the air before it flows into the combustion liner area. There are a lot of pictures on the internet.
Thanks, Ron
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jeffreyguy
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Joined: June 2018
Posts: 51
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Post by jeffreyguy on Aug 1, 2018 21:14:24 GMT -5
I just went with a straight transition for now. I left my good helmet at work so I did all this with $7 fixed shade helmet which was a first for me I like the gentle flare on the Allison, I may try to hydroform something like that later but right now Im just getting the itch to hear it spool up! It wouldn't be difficult to replace my current setup with a larger flared section anyhow so that can be an improvement for later
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Post by racket on Aug 1, 2018 21:22:10 GMT -5
With a straight in transition be aware of the actual flow area , if the gap between flametube and outer can is a bit "tight" , the airflow can be restricted to the point of sending the comp into surge
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