Flame tube design sanity check

[hosedup]

Very clever! So the spark plug is threaded into the outer can and its electrode and ground protrude through the liner?

I was going a different route. Leave the plug threaded into the top plate of the liner (I refer to it as the "head") and its insulator feeds through a mating hole on the outer can. An o-ring is placed on the insulator and a metal ring is screwed down to hold the o-ring and create a seal. The o-ring also allows for axial expansion. I'm also considering using a very long reach type plug used in the Ford 5.4 3 valve engines. If I go that route, it would be long enough to reach to the liner so I could thread the plug into the can and not have to worry about o-rings.



The TV84 engine, do you have and detail pics of the air swirler? I am really interested in building something like that. Not looking for detail drawings (though that would be nice) but something that I could use as a starting point to base a future design on.

The fuel injector, was it a radial series of holes like many do with a hex bolt or did the fuel swirl as well?

[Colin Heath]

Thanks for all the great information, this thread has been really useful at educating me a little on flame tube design which is my current task.

[racket]

Yep , thats how the plug is mounted

A few pics of the TV84 combustor , they're a bit poor as they're pre digital camera days



The swirler was from an oil burning steam boiler system simply welded into the cap , the projection on the cap was for flametube location/fixing into the outer can .

Cheers
John

[hosedup]

Very interesting, thank you for posting.

[hosedup]

I believe I am ready to make my next attempt at a flame tube and am looking for input. Looking at using 9x 0.375 in primary holes around and 9x 0.125 holes on the head plate. If I go this route, does it matter if the primary holes are lined up with the head holes? I drew both on the left. Fuel injector is the same 6 sided bolt that has worked well in previous designs but may have the head turned down so it can be installed from the outside. Same 6 holes though. That is unless maybe I should make a new injector that has 9 holes that line up with the 9 primary holes.

9x 0.375in holes = .994 sq in
9x 0.125in holes = .110 sq in
total 1.104 sq in
Jetspecs suggests 1.10 sq in


This design is a big change from previous attempts.  The top head plate is no longer exposed, it is contained inside the outer housing.  Hopefully this will be a safer design.  Originally I was going to use a dome cut from an old air tank but decided not to.



Thoughts?  If this works well, I may have a source for 304 or 316 stainless for a final design.

[racket]

Hi

I'm of two minds with this one :-(

If I was doing it for myself and using kero I'd have that row of Primary holes at 1/2 flametube diameter from the flat end cap , so 2.5" down with a 5" flametube , and the endcap holes "between" the wall holes to try and create recirculation in the Primary Zone , but with highly flammable propane its not going to make much difference where you place the holes as the fuel will burn .

With your current arrangement I think you will still run a very hot inner end cap as those 9 X 0.125 holes won't do much "work" towards keeping the flame from the endcap , in a previous email I suggested using 1/3rd of Primary air thru the endcap and the remaining 2/3rds thru the side wall , the 1/3rd allows more small holes to better cover the endcap and their outflow to push the flames away from the cap, if you used 2mm dia holes you could use 75 holes spread all over the endcap ,and if you "bent" the holes so that they create swirl within the endcap it can be a positive ,......... the remaining 2/3rds area could be made up of 9 X 8.2mm - 0.32" dia wall holes .

I'd also cut back on the number of Tertiary holes and make them bigger , maybe 9 X 13mm

I only use 304 stainless as thats all thats readily available , works OK .

Cheers
John

[hosedup]

Really interesting ideas concerning the hikes on the end plate. I thought alot about it and this is what I've come up with. You mentioned using 75x 2mm holes. In the US, the closest we have readily available is 5/64 in which comes out to 1.984 mm. I calculated that 76x 5/64 holes is nearly identical. You mentioned bending the holes at an angle. I got to thinking about it and thought that a 30 deg angle to the face but zero deg azimuth would be a good starting point. Since there are so many holes I figured it might be a good idea to distribute them on 2 circles. If I did that, I was also thinking of staggering one circle by half. Thoughts?

[racket]

Hi

Theres no need to use such thick material for your cap , theres only a couple of PSI pressure drop across the flametube wall , quite thin sheet material is adequate which makes drilling the small 5/64" holes easier and they can simply be bent to produce a swirl orientation, with a 5" dia cap you don't need anything thicker than 1mm-0.040" sheet

The small holes need to cover the entire cap area not just an outer ring otherwise you'll still have flames impacting the cap with your current design

Cheers
John

[hosedup]

Jan 21, 2020 18:30:49 GMT -5 racket said:

Hi

Theres no need to use such thick material for your cap , theres only a couple of PSI pressure drop across the flametube wall , quite thin sheet material is adequate which makes drilling the small 5/64" holes easier and they can simply be bent to produce a swirl orientation, with a 5" dia cap you don't need anything thicker than 1mm-0.040" sheet

The small holes need to cover the entire cap area not just an outer ring otherwise you'll still have flames impacting the cap with your current design

Cheers
John

Sorry for long delay, been busy with work and school.

I went with 0.25 thick steel for a couple reasons: Its what I had on hand, allows for making a relief cut for a gasket to flame tube interface and for threads for fuel injector and spark plug. I'm working on a design right now to distributethe holes over a larger area.

But, I'm starting to think about using an extra long spark plug and injector and having them thread into outter head plate and slip fit into flame tube head plate.

All of this has me thinking and I have a couple new questions:

If the spark plug is positioned where P3 is sampled, will the flame travel up the combustor and seat where its supposed to? Or is this an invitation for the plug to roast and disintegrate likely destroying the turbine? Currently I am sampling P3 right before the turbine inlet flange.

If the flame tube was made out of something that won't flake when heated and can go much hotter safety, does it really matter hot it gets? I ask because the local metal suppliers can provide inconel at reasonible prices.

[racket]

Hi

Yep the flame should retreat back to its Primary position .

Even Inconel will fail over time if exposed to direct flame , ordinary stainless steel is adequate for our limited usage times

Cheers
John

[hosedup]

Had some time to play in cad and came up with this.  The 2 medium holes are possible spark positions.  There are 70 5/64" holes. 

I noticed the picture did not post so here's an edit.



I made the holes is curved rows in an attempt to maximize coverage.  That and I thought it looked neat.  The holes will bent over as suggested.  Probably 20 to 30 degrees off axis.

Good to know stainless is adequate. I'm planning on remaking all the hot components out of stainless once the steel prototype is proven.

[hosedup]

I finally had a chance to do some work on the engine.  This is the head plate for the combustion chamber.  There are 70 holes 5/64" (1.98mm).  I am planning on adding 5 more holes, just haven't done it yet.  It is made from 0.060" (~1.5mm) 304 stainless steel.  The holes are not bent over yet, I wanted to try something and I'm curious what you guys think.  I think the chamber will self swirl because the spiral design of the holes will create a series or rich and lean zones and curtains in a spiral following the holes.  As the gases expand in these zones, I think they will be pushed between these curtains.  Or it wont do anything.  I'm curious what everyone thinks.  If nothing happens, ill go ahead and bend the holes over.

The hole in the middle is for the fuel injector.  Same one we've used on several prior builds.  In this case I milled it down to fit the hole.  The 20 large holes along the outer edge are for screws that will hold the plate to the tube.  They are on the "cold" or P2 side of the pipe so not really worried about the turbine eating them if they rattle out.  They will be installed with lock washers and I am considering drilling horizontal holes in the heads and using aircraft grade lock wire.  They screw into a ring that is welded into the face of the flame tube.




Here you can see the underside of the head plate and fuel injector sticking through.  Please note that it will stick out further in the final build and its holes will likely line up with primary holes.  I have not yet decided on a primary hole offset from top of combustion chamber tube yet.  It was suggested half the tube diameter, 2.5".  With the current injector, the furthest I can place the fuel holes is roughly 2 inches offset from the top of the combustion chamber.  I also bent over the outer edge to give some stability and a place to hold a gasket.  I have considered putting some tightly twisted very fine steel wool in a form of an o-ring along the edge of the fold to act as a gasket.  The face of the combustion chamber tube has been machined flat so a gasket may not be needed.








This is how it should stack up once built.  The cad drawing does not reflect the actual thickness of the flame tube or its mounting hardware.  Also ignore the spark plug, its likely not going to be there, it will probably be installed where P3 is sampled.



Thoughts?

[racket]

Hi

Nice "swirl" design , how it will work ............I have no idea , but it looks good :-)

Yeh , Primary holes at 0.5 diameter

Cheers
John

[slittlewing]

I guess it will not swirl, because air doesn't care about the hole pattern and will just enter perpendicularly to plate. But it looks very nice

However, I think it will swirl very nicely if you bend the holes like you mentioned!

Cheers

Scott

[spartablades]

hi i m new here ..i m start to build that project ..a have a turbo with intake ( inducer diameter 7,4 cm)
i want start to fix tha flame tube ... is there somthing like calculator to have all dimensions about flame tube ... about combustion camber ..the holes around the flame tube? i found a calculate to internet but i want to be sure about that project thank you
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