Johansson´s Pocketbike

racketmotorman · Post by **racketmotorman** » Tue May 22, 2007 9:15 pm

Hi Anders

Yep, that'll certainly help with getting plenty of cooling air going thru , and hopefully the increased velocity of that air will keep the lubricant mist in suspension , rather than having it settling out in the shaft tunnel and "puddling" .

If problems still persist you might also want to machine a drainage channel under the turbine end bearing to drain that small "pool" area on the comp side of the turb bearing .

With a reduced "lubricant" flow similar to that which Ash is using , hopefully the problems will be solved :-))

Looking forward to those road test results

Cheers
John

Johansson · Post by **Johansson** » Tue May 22, 2007 9:43 pm

With a reduced "lubricant" flow similar to that which Ash is using , hopefully the problems will be solved :-))

Do you know roughly what pressure drop I can expect in the combustor? I measured an oil flow through the restrictor of 57cc/min at 1 bar but the actual pressure will not be that high since it is dictated by the pressure difference over the combustor, so I am not sure of how much oilflow there really is.

Exhaust puffs from burned oil can be heard at idle so the bearings will most likely survive at the current flow rate...

//Anders

racketmotorman · Post by **racketmotorman** » Tue May 22, 2007 10:40 pm

Hi Anders

The "best ??" way to "calibrate " your lubricant flow is to setup your main fuel flow (kero/oil mix) system and simply bleed off that system 3-5%, between throttle and injectors, at all delivery pressures .

eg,.... on my latest engine there are 15 injectors into the 15 combustor evaporators , with each (at full bore) supplying ~100 ml/m for a total of ~1500ml/m , now 5% of that woud be 75ml/m, or ~3/4 of what goes thru one evaporator injector .

The bore of my injectors are ~0.45 mm , so I've started to setup my "lubricant" bleed (from the fuel delivery main) with a suitably sized (~0.012" - 0.3mm, from memory )restrictor "pill" from a NO2 system (they can be had in a full range of sizes, in small increments of 0.001" at a time ) to provide that 75ml/m maximum flow to the bearings when the injectors are each flowing 100ml/m at full bore .The system hasn't been finished yet , but early indications are looking kinda OK :-))

Naturally, at reduced power settings the bearings , as well as the evaporators, will be receiving less flow . I'll be seeing maybe only 10-15ml/m of lubricant at idle , perhaps even less , but as long as its proportional to the main fuel flow , I'm happy .

Its very difficult to simulate actual flows, as the pressure drops across the injectors into the evaps will be different to the pressure drop between the lubricant delivery tube and the pressures in the shaft tunnel . The shaft tunnel should experience a lower static air pressure than the evaporator inlets because of the expansion that will take place within the shaft tunnel (there being a "restricted" air delivery hole size between combustor case and shaft tunnel interior, I have 2 X 5mm holes) to get static pressures down to that which is behind the turbine wheel , which will be significantly below combustor case pressures due to the required pressure drop across the scroll/NGVs.

I hope this helps .............if not, question away some more :-))

Cheers
John

Johansson · Post by **Johansson** » Wed May 23, 2007 4:34 am

I tried the fuel bleed system first, but since the idle pump is running at 5-6 bar constantly it was difficult to say the least to find a restrictor small enough to get the lube flow down to acceptable levels. The main pump on the other hand is not flowing any fuel at all before the throttle is twisted so bleeding from that line won´t work either.

I guess that I could fit some pressure measuring connections to the engine to find out which pressure the lube container sees, but at this point my main concern is to get the bike started and running. Perhaps later when I start planning for the power turbine... :wink:

//Anders

racketmotorman · Post by **racketmotorman** » Thu May 24, 2007 5:33 am

Hi Anders
:oops: ...forgot you're using a seperate oil container with air pressure activation of the lubrication system , too many emails to different guys with different systems , my old brain can't keep up with it :-((
You'll probably have ~half of P2 in the shaft tunnel/behind the turbine, so if you tested your lubricator at 1 bar that "might??" be the flow when the engine is at 2 bar .
You could probably use the "square root of pressure change" to get a rough idea of flow changes , so if you tested at 1 bar (P2 of 2 bar ), sq root of 14.7 psi is ~4 psi ,so if your actual pressure drop across your metering device is ~half P2 and you're only running say a P2 of 10 psi , that'll give a pressure drop of say 5 psi , sq root of 5 is ~2 , so you'll be getting roughly half ( 4 div by 2) your "tested" lubricant flow , or ~30ml/m .
Unfortunately the actual flows will vary due to oil viscosity changes caused by ambiant temperature changes :-((.............its a hard one to workout ...............bugger !!......perhaps thats why they're mainly gone to metering "thin" kero/oil mixes , which are less affected by temp changes

Cheers
John

Johansson · Post by **Johansson** » Thu May 24, 2007 2:56 pm

Hi John,

Roughly 30ml/min sounds ok, I will measure the consumtion once it is running to find out exactly what it is. Thanks to Multispool I have enough syringe needles to make more restrictors if I have to.

//Anders

Ash Powers · Post by **Ash Powers** » Sun May 27, 2007 1:56 am

Anders,

Is there any way you can make part of this air/oil feed tube with a piece of clear tubing - a sight glass of some sort so you can visually inspect the flow as P2's/RPMs vary?

racketmotorman · Post by **racketmotorman** » Sun May 27, 2007 3:28 am

Hi Ash

What we need is something like those "hospital drips" :-))

Cheers
John

Johansson · Post by **Johansson** » Sun May 27, 2007 8:55 pm

Most of the lube/air delivery hoses are transparent, but I think that it will be difficult to estimate a flow rate just by looking at them.

When I made the oil container I fitted a lenght of clear hose so I can see the oil level, so if I measure its volume at different heights it will be easy to calculate the flow.

//Anders

Ash Powers · Post by **Ash Powers** » Sun May 27, 2007 9:55 pm

Anders,

McMAster-Carr sells flowmeters - go to www.mcmaster.com and go to catalog page 515. They have "easy view flowmeters" that are calibrated for oil.

racketmotorman · Post by **racketmotorman** » Mon May 28, 2007 4:42 am

Hi Ash

Try page 2112 , sight glasses :-))

Cheers
John

Johansson · Post by **Johansson** » Mon May 28, 2007 7:16 pm

Thanks for the advice, but the cost including shipping to Sweden is a bit high. If nothing else works I will have to order one but for now I am going to use some trial and error.

The work on the bike will have to wait a couple of weeks, work and more work is the main reason for that... :-(

//Anders

Jim Berquist · Post by **Jim Berquist** » Mon May 28, 2007 8:01 pm

This may help! You would have to calibrate it to your normal flow. It can only tell you if your over pressure. If you have no pressure. Better then just a sight glass.

0 pressure = pump failure or open line.

Over pressure= injector blockage or pump setting.

It would give some bench mark to adjust your flow with.

Just a thought!

Jim

Johansson · Post by **Johansson** » Tue Jun 05, 2007 9:16 pm

It is the pressure drop over the restrictor that I need to know, not the pressure in the feed hose since that will be the same as P2. I think it will be easier and more accurate to measure the flow directly instead of taking pressure readings and calculate the flow from those numbers.

My new lathe and AC/DC Tig have arrived, so now I can make a new shaft nut that works with the tacho. I will try to get the modifications done to the engine this weekend and run it again before I am off to work again for a couple of weeks...

//Anders

Ash Powers · Post by **Ash Powers** » Wed Jun 06, 2007 8:10 am

Anders,

I take it you have machined the components at the back of the bearing tube like noted in your drawing not long ago. Have you tried running the engine again after making that change to see if the problem still exists?

Since you have an external oil tank that uses P2 to move oil into the bearing tube, why not install a needle valve into the line that runs from the tank to bearing tube and use that to adjust the lube flowrate until you find the sweet spot? You could then disconnect the hoses from the combustor and bearing tube, apply the same pressure into the tank you were running P2's at and use a graduated cylinder or some measuring device to determine the flow volume. Then you could play with different restrictor sizes until you found the size that produces the same flowrate. It would be a sure-fire process of quickly determining the optimal oil flow for your engine - the dynamic range of restriction the needle valve offers will make it much easier to get it finely tuned too - running the engine over a large range of P2s and listening/watching/adjusting until you get it spot-on. Nice info to share too - I'm curious as to what amount of oil an engine/bearings of that size needs, not to mention, you'll have this issue licked or at the least, one step closer to the goal..... (I count it as a step forward even if an attempt doesn't work - at least you'll know what not to do the next time, which is a step ahead. :)

www.pulse-jets.com

Johansson´s Pocketbike

oil flow meter