Waste gate turbo as jet engine.

[ripcrow]

Hi all I'm new to this. Scavenged a Toyota soarer turbo with factory waste gate set at 8 psi. Found instructions on how to build a flame tube and next thing after a experiment with the amount of fuel I have a running engine. Runs well and is reasonably easy to start. Had a few air leaks through bad welds and a leak at the join between the flame tube and turbo. Fixed all that but I still have a problem. All the builds I've seen haven't used a waste gate turbo and I've only got my waste gate to start opening once. Increasing fuel supply steadily the revs build until the sound changes and flame starts coming out past the exhaust turbine at which point I can recover it and keep it going by lowering the fuel rate and blowing extra air into the intake basically re spooling the turbo. What I can't work out is it overfuelling and flooding the flame tube with fuel or starving for air flow into the flame tube. Should the standard flame tube be optimised in any way for the waste gated turbo 

[rythmnbls]

Hi Ripcrow,

Welcome to the forum.
Some dimensional specs of your engine would help us troubleshoot, i.e. what flametube specs did you use? A/R of the inducer and exducer sections etc.

Regards,

Steve.

[ripcrow]

50 mm intake diameter. Flame tube is 100 mm x 150mm long. Outer tube is 130 mm diameter. Exhaust is straight out of the turbine wheel no exhaust tube. Running on propane. Due to turbo design and no money for materials intake to flame tube is scrap pipe and oversized to eliminate flow restrictions but I realise it does create the problem of excessive volume needed to be filled hence the slow increase in fuel allowing the compressor to catch up boost pressure

[racket]

Hi Ripcrow

For starters , disable the wastegate mechanism and fixed the wastegate shut and sealed tight , all gases must go through the turbine wheel at all times , NO bypassing .

Secondly , what size is the turbine wheel exducer , with a 50mm comp inducer you preferably need at least a 55mm outlet on the turb wheel .

Don't worry about excess volumes in the delivery tube , it'll be filled within milliseconds .

The most important question is , what is your propane injector design ??

For propane injection , a simple tube positioned in the axis of the flametube cap , with the end sealed and at least 6 radial holes drilled in the tube to squirt propane radially within the flametube , the holes should be no bigger than 1/16" - 1.5mm , there must be NO axial fuel injection , the radial fuel spray needs to be roughly level with the primary zone wall holes.

Cheers
John

[ripcrow]

m.youtube.com/watch?v=2jaOJP8jbVU Here is a video of it running. Spooling up and throttle response

[ripcrow]

youtu.be/6x0Y-uAQDvM. This is the first run. As you can see the exhaust is too hot and I had no throttle response. Added more fuel supply fixed that as you can see in the other video. Fuel injection is a 3/8 copper tube squeezed nearly shut injecting fuel length ways into the combustion chamber about 1 inch into the chamber

[Johansson]

No oil fed to the bearings???

[finiteparts]

In the first video, it sounds like you are entering compressor surge...(time = 0:22, 0:53, 1:00, 1:24, 1:30...etc)

But, with the lack of fresh oil into the journals, you could also be causing the bearings to reach their limit cycle and the rotor goes into an unstable whirl...which sounds similar. Either one of these would explain your "slow" response.

As the oil heats up, the viscosity decreases...and from the video, it looks like you are boiling the oil off! The film thickness in the journal bearings has to get thinner to maintain the require film pressure to support the load of the rotor...at a certain point the viscosity gets so thin that you start getting a breakdown of the oil film. When the oil film breaks down, the rotor starts to touch the bearing and thus wears the bearing.

If the film thickness gets to thin, from high oil temperatures, the shaft can also start to whirl/whip around in the bearing housing and cause a similar sound. When this happens, the bearings are worn very rapidly due to the huge increase in friction. This is due to the orbit of the shaft centerline going from a condition were it keeps the outer shaft surface away from the bearing so that there is a thin film between them, to a condition where the shaft orbit becomes unstable, jumps out to a higher diameter and the shaft hits the bearing. The noise is transmitted through the turbocharger and sounds very similar to compressor surge. The increased friction would cause the transient response of your engine to also be worse.

Either way, it sounds like you have a issue and the first thing to fix is build yourself an oil system.

Good luck!

Chris

[racket]

Hi

Oil system first .

Second , the fuel injector needs to be changed to what I suggested , NO axial injection , only radially within the FT.

Thirdly , your delivery tube between comp scroll and FT has that acute "corner" just out of the turbo , this will cause airflow problems which will most likely send your comp into surge , we need smooth flowing delivery tubes.

Cheers
John

[ripcrow]

Ok as I said the turbo was scavenged. Leaks oil and bearings are not in the best condition so no pressure feed to bearings. The acute angle is a problem due to turbo design and I've tried to overcome this by using the oversize tube but at times I feel I could still be getting surge. Going to rebuild the fuel delivery and attach an exhaust tube and give it another run and if that don't fix it I'll have to replace the bearings and seals and set up a pressure oil feed. Oil is fed into the bearings now just by filling the tube until oil runs out of the exhaust. The water cooling which now works stops the oil overheating

[ripcrow]

What sounds like compressor surge is actually me altering the throttle

[ripcrow]

Altered the fuel injection and it definitely runs even better. Very little throttle increase has it screaming real quick but now I'm convinced it's getting compressor stall now at lower revs. Will opening the flame tube up allow better air flow limiting compressor stall until higher revs are attained. I can now only get about 1/2 the pace I was yesterday before it stalls. New bearings and seal will help also I realise. Thinking allow better air flow reduceses the pressure on the compressor turbine

[smithy1]

If you don't "pressure lube" the bearings you wont have a turbo to play with....fixing anything else will be the least of your problems. I'm actually surprised it has lasted this long.

Smithy.

[ripcrow]

ordered new bearings and seals today. Apparently one in 5 fall apart dye to ceramic shaft during disassembly so it may be a major job. $400 for a new cartridge with steel wheel which allows greater pressure but bearings and seals for $70. Factory waste gate set at 8 psi but the experts tell me it's safe to run up to 14 psi before delamination occurs. Is there a difference between pressure built for ic engines vs pressure built for jet engines.

[racket]

Hi

Pressure and flow from the turbo is "controlled" by the pistons when the turbo is on an IC engine , the engine rpm and swept volume being the major controller, but on a gas turbine its the turbine stage that does the controlling and the pressure entering it roughly the same as the pressure leaving the compressor stage , but the turbine stage on an IC engine turbo can experience exhaust manifold pressures up to twice the comp discharge pressure .

Theres no real difference between the pressure build for an IC engine and that for a turbo GT , it mainly depends on turbo RPM ,most turbos can run up to ~20 psi even if running in the choked region without overspeeding , if flowing in the middle of the comp map then 25 psi would be reasonable , larger turbos and more modern turbos can go to even higher pressures, it depends on how the compressor wheel/stage is configured.

Cheers
John