Combustion chamber wall thickness

[ckliever]

Hey guys, I’m new to the forum and have been doing a lot of reading. There’s a lot of good info here. So I’m building a turbo based engine and I’m trying to source some 7 or 8 inch pipe for my combustion chamber outer casing. I would like to know what you think the minimum thickness for the outer casing can be. I know that a thicker wall makes for easier welding, but that aside, i’d Like to reduce the weight if I can, and also finding 8 inch tubing isn’t that easy or cheap. If I can go with thinner walls it might open up more outside the box casing options. Obviously heat and pressure are factors too

Thanks for your input!

Chris

[racket]

Hi Chris

Welcome to the Forum :-)

7" stainless air over water fire extinguishers are excellent lightweight outer cans , I've used them in the past jetandturbineowners.proboards.com/thread/40/2-shaft-turbine-kart-build they can often be found cheaply if slightly "worn" , and are pressure rated to >100 psi .

What size is your compressor wheel inducer ??

Cheers
John

[ckliever]

Oh that’s a great idea John. I’m using a t46 turbo and the inducer is about 2.8 inches. So 7 inches would be right on the borderline of enough size, 7.5 or 8 would be perfect I think.

Chris

[racket]

Hi Chris

The turbo in my Link used a TV84 with 3.5" inducer, with a ~140 mm dia flametube , the 7" outer can will be plenty big enough for your turbo .

Cheers
John

[ckliever]

Awesome John. Thanks so much for your input!

[racket]

Hi Chris

Maybe checkout a local fire extinguisher company for "rejects" , to ease any concerns just let them know you don't intend using it for a fire extinguisher but will be cutting it up for the thin stainless tube and end caps for a hobby project ;-)

Cheers
John

[hosedup]

On my last build, we almost used a stainless steel trash can. A little too thin to weld easily but using rivets and high temp RTV should work.

Also search your local area for machine and fabrication shops. They will most likely have a large rolling mill and can make the outer can any size you want. Many shops have big jobs but need little jobs to fill gaps. A local shop rolled something for me and only charged 1/2 shop hour.

Also check your area for metal stores like Metal Supermarket or online like online metals. They will generally cut you what ever you want in the shape you need.

[turboron]

All, much safer to use something with a known pressure rating for a OCC (outer combustion chamber) that is subject to an overpressure failure. I use a modified propane bottle for my unit.

Thanks, Ron

[racket]

Hi Ron

Yep , always a concern with a home made outer can , especially with my 12 inch diameter ones, lotsa surface area :-(

I like the fire extinguisher cans as they're pressure tested to ~300 psi , but went to a section of a LPG gas cylinder for the larger diameter on the GT6041 engine , the 10 inch tubing I used on the 10/98 engine was standard pipe so a bit of overkill , but peace of mind came with it , better to be a tad heavy than having to worry about a burst can .

Cheers
John

[hosedup]

How about the thickness of the flame tube itself? 2mm enough?

[racket]

I use 1.2mm stainless sheet as its not too thick to easily work with , yet thick enough for me to easily TIG weld bits together , I have used down to 0.5mm sheeting but its not robust enough if the combustion causes overheating of the wall.

Theres only a couple of psi pressure drop across the wall so it doesn't need "pressure strength".