First attempt at start and meltdown. Ahh

[ripcrow]

I'm using a garrett gt 3037 turbo with 57 mm inducer and 76 mm exducer on comp and 60mm inducer and 55 mm exducer on the turbine. I made a mistake in building the flame tube. I built it to suit a 76 mm inducer. Oil pressure on got ignition spun up with blower and add fuel and just as it started howling and starting to rev up under its own power it come to an abrupt stop. Seems it had melted the tips off the turbine wheel. 

Now would the flame tube being oversized be the cause of the extreme hot start or is comp and turbine dimensions not compatible. 

[racket]

If the flametube hole area was for a 76mm inducer , nearly 80% bigger flow area , then the airflow through the flametube holes could have been biased towards the larger dilution holes at the expense of the primary zone holes causing delayed/disturbed combustion until too near the turbine stage.

BUT , I'd opt more for the undersized turb stage being the culprit , it should have been able to be coxed into life if the fuel was added slowly and with sufficient starter power applied , but depending on the A/R of the turb stage there could have been thermal choking of the stage which could have sent the comp into surge and made starting impossible .

[ripcrow]

.82 ar racket. And yes the holes in the flame tube were for a 76 mm inducer so I'm up for a new flame tube build. Stupid thing is I realised my mistake in the dimensions but didn't think about the flow holes. It would not have had any pressure drop being so open to flow. Beginners mistake and a expensive one too. I'm not sure I can change the turbine wheel if it fails again unless I change the comp housing and compressor inducer with a custom wheel. Both housings are bolt on so I think it will be a custom housing.

[ripcrow]

Flame tube was very clean inside. Looks to have clean fuel burn right from primary holes right down the length. No hot spots within the tube are visible.

[smithy1]

Apr 20, 2016 5:28:16 GMT -5 ripcrow said:

Flame tube was very clean inside. Looks to have clean fuel burn right from primary holes right down the length. No hot spots within the tube are visible.

Ideally the flame front should start between the primary and secondary holes, so you should be seeing some heat tinting of the flame tube in this area. If the flame front is too far down the flame tube, as John suggests, you'll be getting problems. 

Cheers,
Smithy.

[ripcrow]

Ok so I'm looking at a rebuild of the flame tube. Given the undersized turbine should the tube have a slightly reduced flow area to assist in a greater pressure drop and help prevent choking the turbine.

[racket]

A greater pressure drop will increase the "volume" going into the turb stage exacerbating the situation :-(

[ripcrow]

I thought too much flow had caused a choke situation and the oversized combustor and small turbine had added to the situation. So do I just stick to jet specs recommendations or is it possible to fine tune the combustor to account for the small turbine. Considering it was starting to spool up and self sustain when it stopped dead I think a well built combustor may get this bad ratio ( comp turb size ) to run save buying another new turbo. Also is it worth while angling the combustor holes. Instead of drilling straight through the combustor lining if the holes were drilled at a angle to induce swirl and perhaps slightly against the flame direction to help hold the flame in the tube.

[stoffe64]

You can not have a undersized turbine normalt,basicly follow the rule With a turbinewheel exducer about 25percent larger than the compressor inducer.
Cheers /stephan

[racket]

Yep , stick with Jetspecs .

You could add a diffuser cone to the turbines exhaust to maximise the pressure drop across the stage to help "evacuate" the gases .

There could be a problem with your starter not getting the engine up to self sustain , the addition of extra fuel will generally result in burnt turb tips , its important to have a TOT gauge and keep temps under control during the spoolup .

You shouldn't need angled holes .

Cheers
John

[ripcrow]

Ok I'll stick with jet specs. If I added a diffuser that would put a stop to adding a free power or afterburner to this engine wouldn't it.

[racket]

At this early stage we want to be able to get the engine to run , so an exhaust diffuser will help in achieving that .

Once you've established a start regime that works and is easily repeatable , and you've obtained reliable running data , then and only then would it be possible to consider adding backpressure downstream in the form of a jet nozzle , afterburner or freepower ...............LOL, we need to learn how to crawl before we walk or run ;-)

Slowly slowly with a new engine .

Cheers
John

[ripcrow]

Done a bit of research. I can get a turbine and shaft from a gt 35 with a 68/60 turbine wheel and get my housing machined to suit for $300. Turbine is second hand but is genuine garrett. I'm thinking this might be a better option then buying another undersized turbine and possibly melting it again. It'll be a change from a 60/55 turbine to a 68/60 but still have a ar of .82. I hope to eventually run a free power so I'm thinking it's better to get the gas producer as right as is possible. Any thoughts.

[enginewhisperer]

yep, if you want to run anything with this engine you will need to get the comp / turbine ratio closer to right.

These are a performance turbo for petrol engines, so they're pretty far from correct for a turbine.

You might be better off trying to find a smallish diesel engine turbo instead, which should be cheaper than the repair cost on your current one.

[dieselguy86]

The garrett gt25-35 use the same center housing. Should just be a matter of changing the heat shield and turbine housing, or machining the housing like you said. But you can find used housings on ebay pretty cheap. You may have to also have the compressor wheel hole reamed out to fit the larger quill of the gt35 turbine. I built a custom gt3571 turbo and had to do this exact same thing. Search JDS on ebay it will take you to a guy in north carolina, usa and he can ream the compressor wheel for you. Its hard finding a shop that will do this due to liability concerns.