APS/Ω Gas turbine bike build

[Glen]

Your fan club in the states is pulling for you. You can do it.

[Mobacken Racing]

Thank you Glen!

[Mobacken Racing]

I´ve decided to try to do something about the high idle temps, there is something strange about the temperature curve since it should run a lot colder at low throttle settings.



I removed the compressor housing last night to measure the tip clearance, and I might have found a reason for the high temps. According to an earlier discussion with a friend I should aim for a <0.5mm radial clearance at the inducer that narrows down to a <0.12mm axial clearance at the exducer tips.



To get the exducer clearance down to 0.2mm (tightest I could get without blades rubbing when comp wheel was pushed radially) I had to fit a 0.25mm thinner shim behind the compressor cover, this means that I was running the engine with a 0.45mm exducer tip clearance. Almost 4 times the recommended clearance...



I also checked the turbine wheel clearance and it was ok after I fixed a slight misalignment between the turbine and the housing center.

Since the compressor clearance was so badly off I´ve decided to run the engine again before taking it apart completely, then I will know how much it has affected the temperature profile of the engine. The thicker shim was fitted before the second ever run when a prolonged preheat heated the shaft so the compressor wheel rubbed its housing.

http://youtu.be/3Gd_H8ClmHw

If you look at the maiden run where I ran a tighter tip clearance the engine was idling at 600°C with a jet nozzle fitted (before the turbine wheel started rubbing the NGV plate and I had to shut the engine down). Despite major air leaks and badly designed internal air deflectors the engine idled colder than it does now after years of modifications.

I think I am on to something here...

Cheers!
/Anders

[tallguy]

I haven't read all 46 pages of this thread, so please excuse me if what
I say has already been addressed.

Good luck.  Looks like an interesting project.  I hope the motorcycle
performs as well as you hope it will.

I'm a little surprised by the solid (unsuspended) rear end.  I suggest
you at least consider having a shock-absorbed rear suspension.

If the rear tire leaves the ground, then the engine could rev up and
cause wheelspin, which is highly likely to cause handling and safety
problems.  Ask George Poteet about wheelspin-caused problems!

[Mobacken Racing]

Thanks!

I´ll cross that bridge when I get there, building a suspended frame would have set me back years in the build process before I´ve had everything sorted out.

[Mobacken Racing]

I fitted a second TOT probe today to find out if the high temp readings are caused by a faulty thermocouple, I also removed the jet nozzle to keep the temps down a bit. I have good readings of the temp both with and without the nozzle so it doesen´t matter.



To avoid the rolling red numbers on the dashboard caused by some interference with the GoPro camera frequency I am using a different temp meter for the second TOT, it is the yellow hand held meter strapped to the rev counter.



I also got a mail from my friend Fläppen, he has just calculated the compressor efficiency and it wasn´t at all that bad as I was told earlier. He will get back to me with the rest of the results once the data model is finished.



Cheers!
/Anders

[manta22]

Anders;

Could the high temp reading have been caused by the wrong type of thermocouple. For example, a type K thermocouple has its own calibration curve; any other thermocouple used with a meter calibrated for a type K will give an error.

Regards, Neil  Tucson, AZ

[Mobacken Racing]

In this case the thermocouple used was bought as a set with the gauge, so it should have been calibrated. I have used it for years so perhaps the abuse has taken its toll, earlier it hasn´t been showing any unusual temps so something must have happened to it recently.

[manta22]

Yes, that sounds like it was damaged or its age was showing.

Regards, Neil  Tucson, AZ

[Mobacken Racing]

I did a new test yesterday and I am even more suspicious about the thermocouple now, the new one didn´t register temps higher than 400°C so I have fitted a second one identical to the one I have used from the beginning.



I´ve positioned it at 12 o´clock and further downstream the engine to avoid any hot spots, in the video hot sport can be seen at 9 o´clock and at 6 o´clock where the thermocouple is. I´ll try to get another test done some evening this week to test the idea, so keep your fingers crossed!

http://youtu.be/Ds-4zD9Lbj4

Cheers!
/Anders

[wobblywalrus]

The flowers in the background wave back and forth when the bike is running.  It produces some serious exhaust thrust.

[Mobacken Racing]

Yup, it is surely producing lots of thrust. Imagine all that converted into torque in the freepower turbine later.

I did the double thermocouple test last night, it didn´t show any improvement in temps so I will take the engine apart to see if there is some design issue in the turbine stators, a leaking fuel manifold or anything like that.

http://youtu.be/ywbVvCOiPKs

You can guess that lots of thoughts flew through my mind when the oil tank burst, I was certain that something inside the engine broke so I quickly shut it down expecting the worst.

Cheers!
/Anders

[bbarn]

Finding the issue with the oil tank now makes your test a complete success. Finding it in the middle of a run could make for a huge failure.

[Mobacken Racing]

Finding the issue with the oil tank now makes your test a complete success. Finding it in the middle of a run could make for a huge failure.

Exactly, that would have been a major disaster.

[Mobacken Racing]

After a long, long day full of anticipation I finally could pull the engine apart to check out the internals. What would the core look like after several minutes of full power runs with high temps?



Unbelievably good actually! The NGV section looks fine with the coating still in place although a bit discoloured, vapor tubes ok as well, some slight rounding around the end of the tubes but I had to look for it to see it.



The guide vanes are still as sharp as they were when they were new, hard to believe since they are the most exposed pieces of metal in the engine. The combustor is looking like new as well, no cracks or dents anywhere.



The turbine wheel has some burned oil deposits near the blade roots, might be some minor oil leak past the shaft seal. Other than that it looks fine, no signs of heat soak past the rear bearing.



I removed the fuel manifold and tested it with propane, it was difficult to take a good picture of it since I had to hold the preheat button down to keep the propane flowing. No blocked syringes but two of them were flowing a bit less than the others so that will be adressed later.



And now to the main attraction, the NGV throat area! *drum roll*



I finally think I´ve nailed the temp issue, the throats measures 10mm x 19mm which calculates to a total of 34.2cm2. Take away the impingement nozzle area and I end up at 33.7cm2. That is not exactly near the 31.6cm2 I should have had.



If I block one of the passages I get a total of 31.8cm2 which is close enough I think, might be worth a try before I go ahead and make a completely new NGV.

Cheers!
/Anders