Building the JU-02 gas producer

[Johansson]

I´ll do a flow test tomorrow!

[stoffe64]

Dec 3, 2018 5:18:14 GMT -5 Johansson said:

Dec 3, 2018 5:11:41 GMT -5 stoffe64 said:

Aaarrrrgggh....how about bad luck..try without the scavenge pump Anders!
You will sort it out,cheer up

No worries Stephan, I have gotten past the initial frustration and now find this quite interesting.

Interesting yes ofcourse but also very frustrating i would Think.

[turboron]

Anders, I have a few comments, based on my experience, that may help you sort this issue.

1) Oil viscosity changes exponentially with temperature. Curves of viscosity versus temperature are available via Google.
2) Seal leakage into the sumps from the compressor and turbine cause aeration of the oil.
3) Scavenge pumps must have at least 4 times the capacity of supply pumps.
4) Industrial systems use a aeration tray to separate the air from the oil before the oil supply suction. This is usually a plate with holes setting above the oil level in the tank.
5) Aircraft gas turbines use a centrifugal separator to remove the air from the oil before the tank. You may need something like a centrifugal separator for the bike.
6) Tanks for industrial applications are usually sized for a residence capacity 6 times the oil supply flow rate. Aircraft gas turbines use a much lower number in the range of 2/1. Increased tank volume also helps with the aeration issue.

I suggest you create a diagram of your oil system with all its pump capacitys, etc to help identify shortcomings.

Thanks, Ron

[elventu]

Those pumps have some trouble when air bubbles are sucked in.
I used them for years when I pump vegetable oil in my centrifuge.
The inlet should be large to avoid cavitation, and bubbles made the same issue than cavitation, lowering the flow.
When I do that work I started with 8mm pipe for the inlet, and to have the full flow I had to change it to 16mm.
Also, when I started to cycle the same oil it just passed in the centrifuge, the air bubbles give me some problems.

If your problem is related to air bubbles, you can try to separate them from oil with a deflector in the oil tank, making return oil run on a plain surface will help you in separating it from air.
I do that in my case, but I know it isn't simple to do it on a jet bike rather than filtering used vegetable oil in a 120l bucket 😉.

If the problem is not connected to foam in the oil, as John said, you need to turn the pump faster, but there is the risk of having cavitation on it.

I hope this helps.

[Deleted]

Hi Anders

OMG, that start up is wonderful, the sound the engine is making :-)

I Am with John, try running 24 volt, do you know the ccm of the pump, what rpm is the motor doing

All The Best
Andy

[Johansson]

I'll answer you later, I am at work now. I did find this motor which might be the solution if the one I use now is on the weak side:

www.volcanomotor.com/products/1500rpm_400w_12v_high_torque_brushless_dc_motor-en.html

Cheers!
/Anders

[Johansson]

Thanks for your replies guys!

I agree fully that the problem is related to either foaming or low flow capacity, and I have figured out a way to find out which of them is causing the problem.

The plan is to heat the oil with the tank heater I installed earlier and route the pump line back to the tank with a ball valve at the end to simulate the bearing restriction. This way I will see if the heat is causing the pressure drop or not, if the pressure stays constant it must be aeriation that is the problem.

I´ll do the test tomorrow morning, stay tuned!!!

[turboron]

Anders, do you have good data on the oil temperature when the bike is fully warmed up? Could you measure the oil temperature before heating and after heating in your test tomorrow? A comparison in the difference in viscosity, by referring to a viscosity versus temperature curve, may give you a clue to the next step.

Thanks, Ron

[racket]

Hi Anders

When I was testing the TV84 engine with its "fragile" thrust bearing, I was running ~100 psi oil pressure , it hardly varied during a testing session , ambient 25C temp , large gearpump used, no oil cooler.

Cheers
John

[Johansson]

Dec 3, 2018 16:18:54 GMT -5 turboron said:

Anders, do you have good data on the oil temperature when the bike is fully warmed up? Could you measure the oil temperature before heating and after heating in your test tomorrow? A comparison in the difference in viscosity, by referring to a viscosity versus temperature curve, may give you a clue to the next step.

Thanks, Ron

Hi Ron,

The pressure starts to drop pretty fast so the oil temp cannot have been very high, 30-40c tops. Making a flow/temp chart is perhaps a bit overkill at this point, either the pressure stays constant or it doesent.👌🏻

[smithy1]

Anders, like the others I suspect aeration of the oil....my 6041 keeps very good oil pressure of around 75psi ~5.1bar.... until it starts to warm up to 85C, then it drops to about 55-60psi or 3.7~4bar, I still think this is plenty for our purposes though. I've not seen less than 55psi on the beast....it uses a gravity drain into the tank via an "anti-aeration" plate...perfectly made by John....still the same as the day he made it.

The oil system is one of the few things I haven't changed from John's original design....it just works and works well.

Smithy.

[Johansson]

Dec 3, 2018 16:35:32 GMT -5 racket said:

Hi Anders

When I was testing the TV84 engine with its "fragile" thrust bearing, I was running ~100 psi oil pressure , it hardly varied during a testing session , ambient 25C temp , large gearpump used, no oil cooler.

Cheers
John

Hi John,

Unstable oil pressure has been a curse for Olov and I from day one, along with non-functional tachometers.

I am just about to jump into the workshop pants and go out to start the tank heater, this test should be very informative along with the following flow test at midrange oil temps.

Dec 4, 2018 0:43:14 GMT -5 smithy1 said:

Anders, like the others I suspect aeration of the oil....my 6041 keeps very good oil pressure of around 75psi ~5.1bar.... until it starts to warm up to 85C, then it drops to about 55-60psi or 3.7~4bar, I still think this is plenty for our purposes though. I've not seen less than 55psi on the beast....it uses a gravity drain into the tank via an "anti-aeration" plate...perfectly made by John....still the same as the day he made it.

The oil system is one of the few things I haven't changed from John's original design....it just works and works well.

Smithy.

Hi Smithy,

I´d like to see >5bar oil pressure at all times to be sure that the thrust bearing is keeping a good oil film, rather safe than sorry since I´ve seen what 2 bar oil pressure did to the bearings...

I just want to get this fixed now so I can start focusing on the engine, I must have spent over two years of the bike build time just trying to get the auxilliary stuff working properly.

I´ll report back in a few hours after the test is done!

[Johansson]

I have done some pump tests now up to 30c oil temp, and it is clear that the pump needs to spin faster.

At 12v and 5.5bar I got 5.1 L/min which is too low, at 24v and the same pressure I got 9.3L/min which is much better.

I think the problem is solved, there might still be foaming but I'll sort this out first.👍🏻

The question now is whether to build a 24v feed for the oil pump, or fit a 12v motor that is powerful enough. I think a new motor is the wiser choice since I have a really good LiFe 12v battery and little room for another on the bike.

Hoot hoot!🤠

[Johansson]

I talked with Olov just now and we came up with a third option, a step up converter from 12v to 24v that feeds the pump. Much more compact than a second LiFe battery, simpler than a brushless motor with its electronics and the cheapest of the three options as well.

Here is a 960W 40A converter that should be more than capable of powering the 500w pump motor:

www.ebay.com/itm/12V-DC-to-24V-DC-Step-Up-Car-Power-Voltage-Regulator-Boost-Converter-Transformer/332594870209?hash=item4d7032f7c1:m:mwWWgKL0DidG4Tz4Hi5TiIQ:rk:1:pf:0

Cheers!
/Anders

[enginewhisperer]

I'd be more worried about the step up converter blowing up mid run than a higher powered motor breaking.

They're also fairly likely to not actually meet the advertised specs, and might not be very efficient so you'll pull a lot of current from the battery.