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Author Topic: APS/Ω Gas turbine bike build  (Read 396296 times)
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Glen
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« Reply #300 on: October 08, 2013, 01:07:35 PM »

A small oil accumulator should provide a constant oil pressure, even for a while when the engine is spooling down.

Neil is correct on this.
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Glen
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« Reply #301 on: October 08, 2013, 02:43:23 PM »

Charlie101, Manta22 & Glen: It is a nice thought but not very practical unfortunately, the engine flows massive amounts of oil and takes aprox. 10 seconds to come to a halt from max revs. An accumulator that can provide positive oil pressure at these flows for 10 seconds needs to be huge...

Buickguy3: Thanks! I measured the ring end gap to 0.5mm so that shouldn´t be the problem, I have taken the engine apart now and am measuring everything to figure out what went wrong.



Cheers!
/Anders
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« Reply #302 on: October 12, 2013, 10:49:13 PM »

Hi guys! After some investigation I have figured out why the shaft seal failed on me, I had to assemble the rotary parts and measure the throw in the lathe before I understood what really happened during the run.



The main problem is that the shaft tunnel and the compressor housing aren´t perfectly concentric, I didn´t use dowels to fix the engine core together but relied on the four M10 insex bolts to keep the parts alligned. That turned out to be a mistake since the two could move over 0.5mm with the bolts loosely torqued.



When I assembled the engine before this run I had the misfortune to get very bad concentricy for the engine core so the shaft piston ring seal
rested lightly against its seat. When the engine started this made the seal heat up to the point that the ring grooves collapsed from the pressure from the highly torqued compressor nut.



This was what I figured out when I fitted the assembled shaft in the lathe, properly torqued it was bent to the degree that I didn´t even bother to measure it. I removed the parts from the turbine shaft, measured them and found the shaft seal to be bent by 0.1mm. This in turn bent the entire turbine shaft and produced the imbalance clearly heard during the second start in the video, it bent so much that the compressor wings touched its housing just before the engine came to a halt but luckily without any damage to the compressor wheel.

Right now I am lining up the shaft tunnel and compressor housing in the lathe and preparing to fit dowels so they will fit together exactly the same every time I assemble the engine, a friend will drop by this afternoon with a reamer and dowels so hopefully I will have it done before the end of next week.



It is great to have found the problem, hopefully I will have most design flaws removed from the engine by the time I start racing the bike. smiley

Cheers!
/Anders
« Last Edit: October 12, 2013, 10:52:18 PM by Mobacken Racing » Logged
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« Reply #303 on: October 14, 2013, 03:59:53 PM »

Time to fit a pair of dowels to the engine core.



To get the holes drilled and reamed for the dowels I fitted the JU-01 core to the rotary table in the mill.



After drilling each 5.8mm hole I reamed it at the lowest speed in the mill.



With both holes done I removed the shaft tunnel and fitted the dowels, actually it was a bit difficult because the hole was so exact that the dowels kept popping back out from the air trapped under them. smiley



The fit is perfect, I´ll order a set of reamers for future projects because this is something I haven´t done for the last time.



Cheers!
/Anders
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Rex Schimmer
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« Reply #304 on: October 14, 2013, 10:12:53 PM »

Your reply to the accumulator comment "Charlie101, Manta22 & Glen: It is a nice thought but not very practical unfortunately, the engine flows massive amounts of oil and takes aprox. 10 seconds to come to a halt from max revs. An accumulator that can provide positive oil pressure at these flows for 10 seconds needs to be huge...) may not be quite true, give me the flow rate required, and the maximum pressure that the system runs at and I will calculate the accumulator size. For 10 seconds it doesn't take much of an accumulator to provide up to a flow rate of several hundred gallons per minute. In todays world there are so many accumulator choices for pressure and material that there is probably one that will work.

Rex
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« Reply #305 on: October 15, 2013, 04:36:58 AM »

Hi Rex,

A friend has measured the TV94 rotor assembly oil flow, I´ll forward the numbers once he has answered my email.

One of the reasons for why I haven´t considered this is because I use scavenge pumps instead of gravity drain for the oil, so in case of a power failure for the pumps the bearings are still wrecked since the oil from the accumulator has nowhere to go once it has entered the bearings.

Still I am interested to hear the result of your calculations, if the volume of oil is low enough it might actually be possible to fit an accumulator to the bike.

Cheers!
/Anders
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« Reply #306 on: October 15, 2013, 03:56:04 PM »

Hi again Rex,

Here is my friends reply:

------

Hi Anders

I never did measure the flow through the engine as I was more concerned about simply maintaining oil pressure , as long as the pressure was high enough the the flow was OK .

The pump I made for testing the engine was capable of ~10 litres/minute , any accumulator would need to be at least 1 litre oil capacity from the pressure the fuel pump cutout was set at , probably 45 psi -3 bar if running pressure was 60 psi -4 bar ................a relatively high cutout pressure is a good idea even if the pump was working but pressure decayed as the flow increased due to reduced viscosity from high oil temps , ..........this happened with the 10/98 after extended running, oil pressure dropped below normal design pressure as the oil heated up .

Even if the engine was at max rpm when the pump failed it would only take a few seconds for the rpm to be reduced to quite modest rpm that didn't require pressure lube , the compressor wheel at full power is a 250 horsepower brake without the turbine driving it ..................the overall accumulator volume of oil and air above it would need to be 3 or 4 litres

Cheers
John


---------

I still think I will skip the accumulator, when I get the bearings set up right and fit a quality switch for the oil pump there shouldn´t be any more problems and besides the space available for a 3-4 liter accumulator simply doesen´t exist.

I have ordered an adjustable Hobbs oil pressure switch so I can set the cutout oil pressure for the fuel pump to 30-35psi instead of the 5 or so psi I have now, then I have bought the gas turbine some time to spool down before it runs dry.

Cheers!
/Anders
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« Reply #307 on: October 16, 2013, 12:49:25 AM »

Is there a ceramic bearing that can run dry for a long enough time to let the engine slow down?
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« Reply #308 on: October 16, 2013, 01:00:17 PM »

The gas producer use journal bearings just like a turbocharger, changing them to ball bearings would be a huge undertaking since the rotor loads would be completely different.

Perhaps if I made a hybrid system with an oil assisted thrust washer and cheramic ball bearings but naahh that would be too complicated. smiley
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« Reply #309 on: October 16, 2013, 04:21:17 PM »

Do you realy need pressure ,  a 1 or 2 lit accumulator with a flow control orifice give you 30 sec to a min oil flow just to keep the bearings lubricated on shutdown .
And a collection reservoir of similar capacity could be placed pre scavenge pump

some of the automotive accumulators are an easy design to modify for capacity change  and only 75mm dia 
 
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« Reply #310 on: October 17, 2013, 05:00:51 AM »

A friend  (John Wallis, you know him from JATO maj) gave me a good advice yesterday, he had his oil filter upside down and the air trapped in the filter acted just as an accumulator and make the oil pressure drop gradually after shutoff.

I will do it like this and no complicate things further, I haven´t got much room left so adding more stuff to the bike is the last resort.
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« Reply #311 on: October 17, 2013, 09:07:41 PM »

Anders, I was suggesting a ceramic bushing and not a bearing.  My mistake.
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« Reply #312 on: October 17, 2013, 09:19:58 PM »

A friend  (John Wallis, you know him from JATO maj) gave me a good advice yesterday, he had his oil filter upside down and the air trapped in the filter acted just as an accumulator and make the oil pressure drop gradually after shutoff.

I will do it like this and no complicate things further, I haven´t got much room left so adding more stuff to the bike is the last resort.

Actually that is a really clever idea that the spin on oil filter companies should take up......

If the filter had a sealed rubber ball (accumulator) inside spin on filter and when the engine was started oil pressure collapsed the ball and the filter worked like normal and when the engine was stopped the ball would force the oil out through the system for a short time. No extra plumbing or accumulator tanks just throw the whole thing away each oil change.... smiley

Not sure if something like this exists if not someone could make a whole lot of money from it......
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« Reply #313 on: October 18, 2013, 12:24:19 AM »

Anders, I was suggesting a ceramic bushing and not a bearing.  My mistake.

Cheramic journal bearings would probably lead to disaster in case of an oil failure, the idea with the soft copper alloy bearings is that they will take up all wear to save the shaft and housing. A cheramic bearing would eat through both before the engine has come to a halt... undecided

Cheers!
/Anders
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« Reply #314 on: October 26, 2013, 01:40:16 PM »

While I am waiting for some parts for the bike a friend and I (the productive core of Mobacken Racing) have started building a new jet-kicksled for next years landspeed on ice race at Orsa, twin Schwitzer S500 based afterburning gas turbines producing >1000N of thrust with the driver standing on two 5mm thin spring steel runners...  smiley



With everything dialed in we hope to run at lest 160km/h, hopefully even faster. Should be an interesting ride, two years ago Olovs leg caught fire from the radiant heat from the old jet kicks afterburner, with almost three times the thrust both legs and a fair bit of his behind are in danger... cool

Cheers!
/Anders
« Last Edit: October 26, 2013, 01:42:13 PM by Mobacken Racing » Logged
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