Building the JU-02 gas producer

[finiteparts]

Anders,

Since you have upsized the compressor, you have also increases the compressor aerodynamic torque load.

The usual design fix is to increase the shaft size as the comp torque goes up, thus increasing the face area that the friction has to work across.

Due to this, you can't compare the applied nut torque to the stock turbo and will need to calculate an updated torque...assuming the shaft and nut can provide it without yielding once the shaft comes up to temperature. I think I have a paper about compressor retention and I will try to dig it up.

-Chris

[turboron]

Anders, I grew up on a farm so I know all about shoveling manure. I started driving tractors when I was 7 years old. When I was 15 I worked in the oil fields with my dad. I drove a bulldozer and a winch truck. I have worked on machinery my whole life. I am one of those lucky guys that has always loved my work. What we do here is the most fun since we have no one to answer to except ourselves.

Thanks, Ron

[Johansson]

Chris, I am all ears.

Ron, even if the day job it fun this hobby is top notch. I have learned to know so many fashinating and talented people throughout the years and I wouldn´t be 1/10th as skilled in metal working if it weren´t for the jet hobby.

[Johansson]

I disassembled the rest of the engine tonight, and luckily I found no big surprises.



A bit of soot from the post run flames were expected, but look at this mark on the shaft tunnel. It looks to me like there has been oil leaking past the o-ring seal on the oil inlet. A later check of the seal confirmed that it was damaged.



The bearings look just fine to me, a bit of shine to the pressure pads but they don´t look worn. The same goes for the journal bearings, no problems there.



I wonder why the silicone seal around the shaft tunnel/diffusor plate joint has worn like this?



Some of the welds on the NGV vanes had cracks in them, I will add more filler to the welds to make them sturdier.



Here is the compressor cover, no use trying to interpret the wear marks since there is no way of knowing if any of them are from a rub that loosened the comp nut.



I got the suction oil filter in the mail today, now I just have to wait for the AN10 hose fittings before I can fit it to the suction line.



Cheers!
/Anders

[lofi]

Hi Anders

You've got some interesting discoloration that matches that chowdered seal... While looking over the photos I noticed the cuts in the strengthening webs you made to bring the casting back to flat and it made me wonder if that large diameter casting is distorting under load / heat, causing the front cover to get misaligned, jamming the wheel and also opening up that area letting the seal blow by. I'd put money on the wheel jamming being the cause of the nut unwinding, but that's just a 'hairs on my butt' hunch, to coin a Johnism. Lol! Thinking through Chris' comments on thermal expansion in alloy I thought it worth throwing into the mix of ideas. That casting keeps the front cover in the right place to define the comp clearances, after all.

I know I don't comment much, but thanks for the continued updates. I've literally been following your exploits for years now!

Hope you get it sorted soon either way

Ian

[Johansson]

Dec 10, 2018 19:34:22 GMT -5 lofi said:

Hi Anders

You've got some interesting discoloration that matches that chowdered seal... While looking over the photos I noticed the cuts in the strengthening webs you made to bring the casting back to flat and it made me wonder if that large diameter casting is distorting under load / heat, causing the front cover to get misaligned, jamming the wheel and also opening up that area letting the seal blow by. I'd put money on the wheel jamming being the cause of the nut unwinding, but that's just a 'hairs on my butt' hunch, to coin a Johnism. Lol! Thinking through Chris' comments on thermal expansion in alloy I thought it worth throwing into the mix of ideas. That casting keeps the front cover in the right place to define the comp clearances, after all.

I know I don't comment much, but thanks for the continued updates. I've literally been following your exploits for years now!

Hope you get it sorted soon either way

Ian

Hi Ian,

That theory sounds more and more likely every time I hear it, after all it is a helluva force from 3.4bar air pressure pushing the 30cm diameter engine cover rearwards and since the cover is anchored around the rim of the compressor cover it will be pulled back and to some degree flex depending on how rigid it is.

It would be interesting to open up the compressor clearance and add an abrasive liner to it that will wear down easily in case the blades rub, this way I could run a tighter clearance and let the engine sort itself out.

Thanks for following the build process, it is a long and winding road we are walking together but hopefully there is a naked maiden with a pint of beer at the end.

Cheers!
/Anders

[stoffe64]

Dec 10, 2018 16:29:16 GMT -5 Johansson said:

I disassembled the rest of the engine tonight, and luckily I found no big surprises.



A bit of soot from the post run flames were expected, but look at this mark on the shaft tunnel. It looks to me like there has been oil leaking past the o-ring seal on the oil inlet. A later check of the seal confirmed that it was damaged.



The bearings look just fine to me, a bit of shine to the pressure pads but they don´t look worn. The same goes for the journal bearings, no problems there.



I wonder why the silicone seal around the shaft tunnel/diffusor plate joint has worn like this?



Some of the welds on the NGV vanes had cracks in them, I will add more filler to the welds to make them sturdier.



Here is the compressor cover, no use trying to interpret the wear marks since there is no way of knowing if any of them are from a rub that loosened the comp nut.



I got the suction oil filter in the mail today, now I just have to wait for the AN10 hose fittings before I can fit it to the suction line.



Cheers!
/Anders

I wonder if that broken silicone seal can be because of the alloy shaft tunnel?,maybe it is bending or flexing because of the loads?..maybe this part should be made of Steel or stainless??
Very interesting build this, im following your work with it and i know you Will get it running flawlessly.
Cheers/Stephan

[Johansson]

Dec 11, 2018 1:22:10 GMT -5 stoffe64 said:

I wonder if that broken silicone seal can be because of the alloy shaft tunnel?,maybe it is bending or flexing because of the loads?..maybe this part should be made of Steel or stainless??
Very interesting build this, im following your work with it and i know you Will get it running flawlessly.
Cheers/Stephan

Hi Stephan,

No flexing there, four M12 bolts are holding the parts together.

There must be some kind of flow passing by the seal, I am guessing the scavenge pump is pulling hot air from the engine core into the shaft tunnel and this heat is what damages the seal.

[stoffe64]

Aaahh,Difficult and you must have the scavenge pump for it to drain the oil out properly. Hmmm

[elventu]

Maybe a vent to limit the vacuum in the tunnel can reduce the problem mantaining the scavenge pump efficiency.

[CH3NO2]

Anders,

Is the seal damaged from a chomp or a burn through? Without char, it looks torn but it's a little hard to tell from the pic.

BTW congratulations on getting the engine working at 4 bar. Even if there was a temporary setback, it's an admirable and fascinating accomplishment on every level.

[Johansson]

The seal is definitively damaged from heat/wear, it is impossible to "chomp" it during assembly.

It is most certainly an idea to build a spring loaded valve that sets the maximum under pressure in the scavenge line, or to be correct it would set the maximum pressure difference between the suction line and the atmosphere.

Since the pressure inside the engine will to some degree seep into the oil drain through the shaft seals this valve would work perfect, it would sustain a constant under pressure no matter how much P2 air that bleeds in. When I ran JU-01 I tested this and at 2 bar P2 I had something like 1 bar pressure in the suction line, well above atmospheric pressure but it still maintained good suction since it is the pressure difference that matters.

Thank you very much CH3NO2! (damn nicknames! ) This is a really great journey for me and I like to view the setbacks as valuable lessons instead of failures, so I don´t mind the occasional hickup in the development.

Cheers!
/Anders

[jetjeff]

Hi Anders,

I guess if it were "easy", there wouldn't be entire forums started like this one.

I agree on following this endeavor making you a better machinist,,,I firmly believe my engine builds led to a different career path for me at 57 years of age and couldn't be happier.

We hold tolerances down to tenths (i.e. .0002") at Blevins Screw Products in Flint MI,,,quite an achievement.

Regards

Jeff

[Deleted]

Hi Anders

So glad you not found any other bid worry's, should be back up and running stronger soon I hope :-)

[racket]

Hi Anders

Compressor slippage test completed .

Test rig


The oil slinger and piston ring holder were both assembled onto the shaft with lubrication on all surfaces , I used my usual synthetic lube as on the test stand , the end of the "compressor wheel" was also lubed , the comp nut was fitted using Loctite 262 and torqued up as per usual , and left for 24 hours to set.

The "torque arm" was 11 inches centre to centre, the first test resulted in 25 kgs pull and nothing happened , 25 kgs at 11 inches works out at just over 50 foot pounds .

What now me thinks , ..........a length of pipe was found that slipped over the adjustable spanner and a hole drilled in its end for the spring balance to attach at a 22inch centre/centre.

Second test obtained 16 kgs before the "comp" started to move , 16 kgs at 22 inches is ~65 foot pounds of torque .

The interesting part was that the nut didn't move, the comp mearely slipped between the nut at one end and the piston ring holder at the other , the piston ring holder and oil slinger remained stationary.

Now , assuming you had 70,000 rpm and 4.4 PR at 75% comp effic with ambient of 15 C , this would result in a ~203 C degree rise in compression , requiring ~124 HP/lb/sec of air flow.

Your 0.9 Bar in the jetpipe will have produced ~1,900 ft/sec at the exhaust , your 750 C - 1023K jetpipe temp would have produced a density at the exhaust of ~40 cubic feet per pound , your 89 mm jet nozzle ( 90 mm hot) has an area of ~0,06847 sq feet , multiply by our 1,900 ft/sec gives us a maximum of 130 cu ft per sec , divide by our 40 cu ft/lb and we end up with a max flow of 3.25 lbs/sec , neglecting boundary layers and other losses , we're looking for max loads on the turb wheel here.

3.25 lbs/sec X 124 HP/lb/sec = 403 HP required by the comp , 403 HP at 70,000 rpm = 30.2 ft lbs of torque , less than half what I found in my static test this morning .

Your comp rub was caused by the wheel contacting the housing, not from slippage due to excessive power requirements.

I'll repeat the test after degreasing parts and see what difference dry parts make .

Cheers
John