Newbie with a VT50 Turbo

[maritimer95gt]

Wow, that thing looks really good! I'm wondering then if I should use flat sheet metal like you did and make a tube because the thinnest tubing I can get in a 5" diameter is .065. That probably would be difficult to bellmouth while trying to keep it relatively round. I could always heat it though. What would you recommend?

[racket]

Yep , its possible to use flat sheet stainless and drill the holes and bellmouth them before rolling into a tube and welding the joint , the weld doesn't have to be perfect as a few leaks won't make any difference .

If you go with the 0.065" WT tubing , just make the holes a tad bigger than recommended and leave them plain

Cheers
John

[maritimer95gt]

Which would be more beneficial to performance?

That's what's more important to me either way.

If making the tube out of sheet metal is better, what is the widest I should make it within my 6"id combustor while still allowing sufficient air movement around the flame tube? Should I taper it at all?

What gauge do you recommend for it?

Thanks again for all your help!

[racket]

Hi Alex

Performance from our engines is a matter of reducing losses to a minimum as its not possible to run them any hotter or faster in an attempt to increase power .

You need a half inch gap between flametube and combustor wall so that the air can efficiently transition thru the wall holes .

To reduce losses across the flametube we need to have the hole sizes as big and as aerodynamic as possible within the constraints imposed, bellmouthed holes will reduce losses.

1.2mm -0.050" stainless sheeting can be bellmouthed and rolled , and is easily welded , 1mm -0.040" is probably as thin as you'd want to go , thinner materials are harder to weld and don't cope with the stresses quite as well , though having said that I have used them successfully down to 0.5mm - 0.020" thickness .

You will need to reduce the diameter of the flametube to that which will fit into the scroll inlet so that there is a smooth transition with minimal losses .

Cheers
John

[maritimer95gt]

The turbine is coming along nicely and I will have pictures posted later tonight. Only a few more things before I get to start it up for the first time!

[maritimer95gt]

This picture shows the heat exchanger to preheat the diesel.  I just wish the site would let me upload higher quality picture so you guys could see it better.

[maritimer95gt]

Here's the turbine all set up on the test stand ready for the first spool.

[maritimer95gt]

I am a little disappointed with the jet spec program. After the first run I could tell there were some big issues. It runs extremely rich on propane and is almost impossible to idle. I'm getting a lot of flame exiting the exhaust with very little thrust. Any help would be appreciated.

[racket]

Hi Alex

What sort of propane injector are you using ??

Jetspecs will produce a running engine if you followed it specs .

Cheers
John

[maritimer95gt]

Well, I ran the numbers with jet spec and built the flame tube and combustor to spec except for a little extra length in the overall combustor. (As I think you said that it shouldn't make too much of a difference). I have just a straight through 1/4" line backed off 6" from the primarys to allow for expansion. Bluing on the flame tube starts evenly around the flametube immediately after the primarys. The same exact setup with a 90 degree ball valve has proven to work very well on a slightly smaller turbine that belongs to my buddy.

[racket]

Hi Alex

Propane MUST be injected RADIALLY within the flametube , it must NOT be injected axially , the quantity of propane required will produce a jet of fuel straight down the middle of the flametube if an axial injector is used , combustion won't commence until it mixes with air and that is often within the turbine wheel .

Squeeze the end of your 1/4" line off so that its sealed and drill 6 X 1/16" diameter holes equidistant around the 1/4" tube sidewall, this will produce a "wagon wheel" spray pattern of fuel at the primary zone end of the flametube and your engine should work just fine :-)

Cheers
John

[stoffe64]

hello!

that heat exchanger you made, how does that work?, have you tried to run the Engine with diesel or kero?
what size of the flame tube and outer can?
propane injector must be a radial one
cheers/stephan

[maritimer95gt]

I'm currently out at sea for the next few months from what it looks like so I can't get you the dimensions of the flame tube mainly because I can't remember them off of the top of my head. The heat exchanger is actually for running diesel. I built it on the principal that heated diesel will atomize from the spray nozzle much better allowing for a much more even burn. While starting the engine, I use propane to heat everything up and slowly bleed diesel through the line so that it doesn't cake in the line. Then when I'm ready to put the "spurs" to it, I open up on the diesel and cut the propane.

[stoffe64]

hello Alex!
thanks for your reply even though you were on the sea,really appreciated, how did it run the Engine?, i saw you had some problems with it, did you solve that?, a very interesting build i thought, cheers/stephan

[mitch]

Just my 2 cents on the flame tube size. I used a 6" ID combustion chamber and a 5" OD flame tube. The only problem I ran into was making evaporator tube mounting plates and flame tube connecting flanges that fin in the combustion chamber without rubbing. Another problem you might run into with the swirl and an offset air intake tube is the high pressure zone created by the pressurized air entering. I had similar problems to RCdon in terms of a hot spot being directly across from the intake tube, which I fixed by welding over some of the holes on the hot side, and opening up some of the holes from 1/4" to 3/8" on the high pressure, or cold side. This fixed up the hot spot problem almost perfectly first try.