I'll get the measurements soon, but... Very close clearances. It was my first suspect. The turbine to nozzle guide vanes are like a piece of standard notebook paper. So definitely not the turbine side. I think I had .015" from the compressor outer tips to the inside front of the cover. And about .010 around the tips to the inducer. I actually took about .020" off the diffuser wedges, trying to get the cover closer to the compressor.
.015" gap on the compressor exducer side is quite a lot. Reducing the wedge height is what I would have done. It's kind of tough to really measure the clearance on the blind side of the compressor blades, I've though about using a small ring of modeling clay to check it.
Kurt Schreckling has stated in his book that micro turbines using turbocharger compressors are very sensitive to tolerances in the axial direction.
I forgot to mention that Kamps recommends to get the turbine running reliably on propane before even thinking about liquid fuel. Things can go south in a hurry on liquid fuel especially without a FADEC.
Yep , 0.015" is a lot of clearance for such a small wheel , I try for 0.012" with my larger wheels which equates to ~2.5% of tip height , no more than 0.008" for you .
But even with 0.015" clearance it should be possible to get up to a higher P2 .
I check clearances using masking tape , each layer represents ~0.003 - 0.004" , you'll only need a couple of layers , just cut small squares of tape and fold over the exducer , you only need it in 3 or 4 positions , then replace and tighten the front cover and check for free movement of the rotor , if its still free , add an extra layer or two until you get a firmish drag as you rotate it .
Post by z28guysteve on Oct 9, 2021 17:39:10 GMT -5
Thank you all. I have a new diffuser I designed being machined in China. In the mean time I'll try to close up the front cover clearance some more by filing down the wedges until the desired clearance is achieved. Ill have to get back to everyone next week. I'm an airline pilot and I have a 5 day trip tomorrow.
Post by z28guysteve on Oct 16, 2021 11:37:39 GMT -5
I was mistaken on the clearance when I quoted it from memory so I re measured it.
Turbine to Nozzle guide Vane is 0.008" inch or 0.203mm Compressor inducer to inlet side clearance is also 0.008" inch or .203mm Compressor exducer face to inlet face clearance after sanding diffuser vanes is .0035" or 0.089mm or two pieces of office clear tape definitely create contact.
Turbine major diameter is 51.181mm Turbine Minor diameter is 32.766mm Case diameter is 83.16mm
After checking out your video again I notice you are trying to get the engine to run on a rather small propane cylinder , may I suggest using a larger 20 lb/9 kg BBQ cylinder simply to allow sufficient gasious fuel flow to the engine, also make sure there isn't any "safety" device on the cylinder.
Once you have the engine setup for propane , you don't need to be concerned about your vapouriser tubes and fuel injector lengths/orientation as propane will burn .
The propane will negate any combustion issues , its fast burning and will burn over a wide air/fuel range .
The removal of the jet nozzle will maximise the pressure ratio across the turbine wheel allowing it to power the comp with lower temperatures , your current ones are way too high , a bit of red colour is OK , but orange/yellow is a NO NO .
Which parts of the engine did you make from plans and which parts are as "supplied" ??
A heap of pics will help explain things .
And as Jeff mentioned , the comp wheel dimensions are important , so if you could supply them it'd be appreciated
Post by z28guysteve on Oct 17, 2021 4:39:03 GMT -5
Every part was supplied except the basket, but numerous people have said the diffuser is very wrong. The wedges equaled the number of comp blades, they have square blunt edges on the wedges, and they don't expand at all just straight passages. I tried on propane and can only get at most 2.5 psi behind the diffuser no matter how fast I spin it. Even with the BBQ tank now