Johansson´s Pocketbike

[Johansson]

After taking a years vacation from the bike to catch up with some other projects I have started to think about it again. I got so sick of the troubleshooting last year that I needed some time off...

Before I do any major changes to the engine I will try to run the engine on propane only to see if the combustor behaves differently, the bearing housing will be rebuilt with the seals fitted on the shaft so the used oil can be collected in a container under the engine. I will also move the preload to the front bearing to make it less likely that the preloaded bearing will stick due to deposits from the lubrication.

Feels good to be back on track again!

[racketmotorman]

Hi Anders

Good too see you're back working on the turbine )

I'm still having bearing problems with FM-1 despite running a recirculating lube sysytem , the turbine end bearing which also acts as the thrust bearing keeps wearing out from overload (

I'm going to attempt "pressure balancing" to remove most of the axial thrust loading caused by the static pressure on the backside of the comp wheel which isn't being "balanced" by static pressure on the turbine "disc" as what happens when using an axial turbine wheel , my radial inflow turbine wheel only has blades so no oportunity for a balance load .

Will be fitting an 85mm dia disc onto the back of the turbine wheel , heat shrunk onto the hub over the piston ring seal boss , with labyrinth seals at outer edge and at the hub to replace the piston ring .

This "rotating piston" will have full P2 pressure air fed into the upstream side cavity , hopefully putting an axial force of ~250 lbs -120Kgs onto the turbine wheel , effectively balancing the axial load on the rear of the comp wheel .

All the best with your new experiments )

Cheers
John

[Johansson]

Hi John,

I´m sorry to hear that you still have problems with the bearings. An interesting approach to the problem with the pressure disc, I keep my fingers crossed for you. By the way, do you post your progress on the engine somewhere else than in the Yahoo DIYgasturbines group? I try to keep myself up to date but the text based forum is a pain in the ass to read through when one is used to phpBB forums...

My thought was to try propane first to find out if the combustor is causing the noice, at the last video bursts of flame could be seen through the turbine wheel that might indicate combustion instability. Another thing to check is the shaft spacers and if the ends are perfectly flat, if not the shaft might bend a little when the compressor nut is torqued down and cause imbalance.

First of all I need to find a way to take the bike with me the next time I visit my parents, it might just fit in the back seat of my car if my girlfriend decides to travel light...

[racketmotorman]

Hi Anders

Yeh its important to check the squareness of bearing faces , I now lap them in using valve grinding paste and some "slave" bearing inner rings ,the turb end bearing face to hub interface has to be done using the turbine shaft for alignment of the inner ring , but for the other interfaces I use a "mandril" so that the parts can be removed from either end as even the smallest amount of valve grinding paste deposited between shaft and sleeve or bearing inner can jam the part on the shaft and easily wreck a finely ground surface when metal "picks up" , I learnt from bitter experience (

How much preload are you using on your bearings ??

Is the turbine bearing the one taking the axial thrust load ?? .............the shaft should to be "in tension" so that rotor dynamics are "favourable" .

Unfortunately FM-1's build progress has only been posted on DIY , not the best Forum for following these things over a long time frame .

LOL........girlfriends never travel light ..................you might need to leave her at home on such a serious journey )

Cheers
John

[Johansson]

I´ll have to check the preload when I take the engine apart, it was a year since i did any work on it and I tend to forget things like numbers and names after a week or so...

The turbine bearing is the one that is preloaded with the spring pushing the bearing towards the turbine wheel, so with the front bearings outer race fixed in the tunnel it is fair to say that both bearings share the axial load at the moment. The front bearing seems to survive much better than the rear one, mostly because it runs cooler I guess.

Please explain what you mean with favourable rotor dynamics, I went to work 04:00 this morning so my mind is a bit slow...

Why not start a thread here on the engine where you can post all previous pics and cut and paste your progress reports? "Hint hint wink wink"

[racketmotorman]

Hi Anders

Its supposidly better if the shaft is in tension , this info was provided by a knowledgable guy whose done a lot of work on micro turbines .

With our engines running radial inflow turb wheels , as with normal turbochargers , the axial force is always forwards towards the comp , which means the axial loads should be taken on the turbine end bearing with the comp end bearing being free to move axially .

I realise this isn't how turbos are setup , they have the thrust bearing at the comp end , but they also run "brass bushes" with the lube providing lotsa damping of rotor dynamics .

FM-1 has both bearings running in bronze cups with the preload spring forcing against both cup , with ~0.005" endfloat before the cups bottom in their shaft tunnel recesses , this way both bearings are capable of taking axial loads allowing the shaft to be in tension no matter what happens .

LOL...I might do a Thread for my next engine , the "9/60' ...............9 inch case, running a GT60 comp wheel )

Cheers
John

[Johansson]

With our engines running radial inflow turb wheels , as with normal turbochargers , the axial force is always forwards towards the comp , which means the axial loads should be taken on the turbine end bearing with the comp end bearing being free to move axially .

So you mean that the front bearing should be able to move on the shaft as well as in the bearing housing? I use a spacer tube between the both bearings inner races so when the compressor wheel and its spacer is fitted both bearings are fixed on the shaft and cannot move at all.

[racketmotorman]

Hi Anders

Yep, same spacers etc with FM-1, the inner raceways are locked solid on the shaft , but the outer raceways in their bronze cups are free to move axially by that 0.005" , the whole shaft can be moved axially back and forth by that 0.005" , the 25 lb-11 Kgs of preload spring keeping the raceways tight against the balls no matter where things are positioned , the bronze cups are what slide that 0.005" in the shaft tunnel .

Cheers
John

[Johansson]

Hi Anders

Yep, same spacers etc with FM-1, the inner raceways are locked solid on the shaft , but the outer raceways in their bronze cups are free to move axially by that 0.005" , the whole shaft can be moved axially back and forth by that 0.005" , the 25 lb-11 Kgs of preload spring keeping the raceways tight against the balls no matter where things are positioned , the bronze cups are what slide that 0.005" in the shaft tunnel .

Cheers
John

Thanks for the explanation John. How do you keep that tight 0.005" clearance when things start to heat up? In the beginning I had a problem with the comp wheel rubbing the housing when the engine heated up, it turned out that the rear bearing preload didn´t work properly so when the shaft elongated from the heat it pushed the comp wheel a couple of .1mm´s too far forward. I had to check the clearances a bit better after that...

Any recent videos of the engine?

[racketmotorman]

Hi Anders

The 0.005" is a "compromise" figure , but as I'm running a steel shaft in a steel bearing shaft tunnel with ~400ml/m of lube , the temp differance between shaft and housing ( it has a heat shield around it) shouldn't be anymore than maybe 50 deg C, and as the shaft tunnel distance between bronze cup recess to bronze cup recess is only ~2" , and with a expansion ratio of ~0.00001 , that only amounts to 0.001" , so even with 200 C degrees diff, which would be impossible with a T2 of <200 deg C , there'd still be 0.001" end float .

I run ~0.012" - 0.3mm clearance between comp blades and front cover , but my last engine failure had the comp contacting the cover and ~0.5mm ground off all the blades .

I do have some recent video of the last "malfunction " , unfortunately the vid is fairly big and I'm not sure how to "cut and paste" the best bits into something suitable for Youtube (...............I might try doing it today )

Cheers
John

[racketmotorman]

Hi Anders

Try this Link ............ http://au.youtube.com/watch?v=VX5U8DlBzzk .............the "Fat Lady" singing sweetly , crank up the audio for some semblance of the volume of sound coming out of her

Right at the end you'll notice flames , this is when the NGV's closed up as bits of turbine wheel hit them causing the comp to surge .

Enjoy

Cheers
John

[Johansson]

The engine is finally in my workshop waiting to be mounted on a test stand, I haven´t decided yet if I sould give it a go on propane or if it is better to rebuild the engine for rear bearing preload first. It would be nice to hear it spool up once more but it would be less nice to damage my 300$ hybrid bearings just for some playtime.

The combustor will eventually be rebuilt with a single centred spray nozzle in the vapourisor just like RC-Don has done on his GR-7, a single vapour pipe with four J-tubes connected to it at the bottom. It will be easier to change fuel nozzles that way and I will get much more heating area than before.