Building the JU-02 gas producer

[Johansson]

Dec 9, 2019 22:56:10 GMT -5 racket said:

Hi Anders

LOL, .........I understand your concerns about the fuel when riding the bike , it sorta entered my mind when screwing the TV84 up to red hot when it was sitting directly under the fuel tank between my knees , wisely you've got your tank down below the engine .

Hopefully all will be OK with the JU-02 without changing from kero :-)

Cheers
John

Hi John,

That was the whole idea with the underhung fuel tank, I´ve sprung enough fuel leaks over the years so I wanted to place it so no dripping fuel could ever reach the hot parts.

So far things have looked good with JU-02 so I have high hopes, I was up close to 70.000rpm when the compressor wheel let go last time I ran it and the temps looked good.

Cheers!
/Anders

[finiteparts]

Hi Anders,

I thought that I would add a few comments on the placement of tc's downstream of radial turbines.

First, remember that the amount of energy extracted is not consistent across the discharge plane of the turbine due to the variation of the tangential velocity as the radius is changes.  So, there will exist, by default, a radial temperature gradient with the hottest gas flow occurring near the shroud and the coolest gases being near the hub. 

This is why you see the tips glowing first when things get hot and also why you see the tips sling off.  The outer portions of the blades not only heat up faster than the rest of the rotor, but that is also where the blade flexes the most during vibration and has a large g-field stress on them.  As metals get hot, the tensile load capability of the metal decreases.  Once the tips get hot enough, the tensile load capability falls below the point where it can resist the g-forces pulling on the tip.  Once it exceeds the ultimate stress capability of the material, you fracture off the blade tips.  Many people mistakenly call it "melting" off the tips, but in reality, it is actually a tensile fracture issue.

This leads to the question, are you trying to measure gas temperatures to make sure you don't overheat the tips of the wheel or are you trying to use the EGTs to calculate the performance after the run?  Each of those cases would mandate a different location of the tc.  The first would require that you put the tc's with a small penetration depth such that you are measuring the gas flow near the shroud.  The second case would suggest that you place the tc's near the mean average radius so that you could get an area weighted average gas temperature, which is a better fit for a 1-d performance calculation.  A similar line of thinking would determine the axial location after the rotor, closer to capture the high temperature shroud gas temps, or perhaps a bit farther away if you wanted a more mixed out gas temperature for performance estimation.

Now there will be more 3-d effects that will change the exit profile and muddy things up a bit, but the general idea is to look at the radial temperature profile effects.  I still say that you should look into radiation shields for any tc near the turbine exit plane, especially since the view factor of the tc could easily have a direct line of sight to the hottest gas entering the shroud region.  If you are comparing multiple tc's, they need to be placed very accurately to the same radial depth so as to not incur noticeable temperature variations.

I am looking forward to seeing it up and running.

Good luck!

Chris

[racket]

Hi Chris

Temp measuring is to try and find if theres any potential combustion problems resulting in abberant temps between segments of the engine , Ander's JU-01 engine ran with extremely high TOT temps being recorded in the interstage ducting , temperatures which would have seen T I Ts at levels the gas producer turbine would not have coped with , yet it escaped any damage , so the thinking is that there may have been interstage combustion/hot streak ?? occuring and affecting the single thermocouple , the addition of 4 extra thermocouples should provide answers.

The video of Anders last speed run showed a red hot freepower wheel some time after shutdown , yet all the vid I have of my freepower runs indicate freepower wheels cool very quickly once the power is reduced , a few seconds and the glow is gone , something strange was happening with Anders engine .

Yep , we'll all be looking forward to seeing it running again :-)

Cheers
John

[Johansson]

Hi Chris and John,

Speaking for myself I am only interested in knowing how the freepower turbine is coping with the temps, once I start running the bike the only performance number I am interested in is the top speed after a mile and the acceleration curve on the GPS logger.

Interesting info about the temperature change when further out in the interstage duct, it makes sense.

I agree that the temperature on JU-01 was a mysterium, interstage combustion sounds like a reasonable explanation for the very hot freepower wheel. Although the temps while running it as a pure jet was also a bit high, I hope that the new owner will figure out what ails it.

Cheers!
/Anders

[pitciblackscotland]

Hi Anders,
Yeah i will work it out hopefully just take small steps at a time. I had a similar issue with the JFS you will see in the vid some of the NGVs glowing red, i had the temp probe in the wrong spot.
Cheers,
Mark.

www.youtube.com/watch?v=PmDDDzl3wGc

[Johansson]

The temp sensors arrived today, neat little buggers.



Here is one installed on the interstage duct, they will be in the way of my feets when riding but for static testing this will do.



Cheers!
/Anders

[Johansson]

During the last week I have been wiring up the bike, cleaning the filters and generally setting up the systems.



With the tanks in place I could do an oil pressure test today, with cold 0w30 oil the pressure gauge bottoms out at 8bar oil pressure despite having the internal relief valve fully opened. That is both good and bad news, I had hoped that the pressure would be within the scale when the relief valve was opened. I´ll try to heat the oil tank up and test it again later.



Unfortunately the high placement of the scavenge pump seems to cause problems, I found that after the test the engine cover had filled up with a bit of oil which it never did when the scavenge pump was placed below the engine.

Bugger deluxe, I thought I finally had found a good place for the scavenge pump but it seems like I have to move it. The first thing to do is to temporarily fit it lower to confirm that the high placement is the problem.

No worries, I´ll have this bike sorted out and road ready by the end of 2030 or so...... *LOL*

Cheers!
/Anders

[lofi]

Is there a way you can put the scavenge pump inside the tank? Maybe mount it to the inner side of a removable plate or suchlike?

[Johansson]

Ooooor, I could perhaps have checked that I didnt wire the scavenge pump backwards. *manic giggle*

All is well then, just Mr Stupid doing his thing.

[Johansson]

Things are turning from good to even better, I found that the oil pressure gauge bottomed out even with the oil pump disengaged so I checked the wiring and found that the gauge wasnt properly grounded.

With a new ground wire the gauge reacts perfectly to the internal bleed valve and I can adjust it from 3 to 7 bar oil pressure!

All is just f-ing perfect then, I'll sort out the last bits and pieces and make an arrangement for a track weekend some time this summer!😍😍😍

[Johansson]

During the oil pressure tests I have found that the oil in the scavenge line slowly drains back to the engine and leaks past the seals into the outer cover, I made a one way valve that slowed the leakage but didnt stop it completely.

Another idea is to add a small catch tank under the engine with the suction line at the bottom, this way the pump should keep it sucked empty during running and the accumulated oil in the lines will partially fill the catch tank and not reach the engine.



That is the theory at least, I'll soon find out if it works in real life as well.🙂

Cheers!
/Anders

[Johansson]

Nahh, the catch tank idea didn´t work. At least not with the volume this one had and a larger one won´t fit. It quickly filled up and oil started leaking from the engine cover drain again.

No harm done though, I gave it a thought and found that a simple drain valve will do the trick. I need one anyway to drain the scavenge line before disassembly so I can just drain the lines in a can after a run and pour it back into the oil tank.



It fits at the lowest point on the scavenge line and the valve is easy to reach even with the fairings on.



I also fitted a vaccum gauge on the scavenge line to have a visual that the pump impeller is doing its job, with 7 bar cold oil pressure I had -0.2 bar in the scavenge line which is good enough.



I am sorry for the crappy pic quality I am posting nowadays, my Iphone 8 isn´t exactly good at taking pictures and a scratched up and oily lens doesen´t really help.

Cheers!
/Anders

[Johansson]

This morning I made a new propane preheat hose and fitted it along with the starting air hose, little bits of work that slowly gets me closer to a test start.

I am also thinking of making an intake screen for the engine, I have bought a large mesh stainless net that I can silver solder together into a large area screen that fits to the bellmouth.

Even though small pebbles and sand will get through it will stop lose wires and fingers from getting sucked into the engine.👍🏻

Cheers!
/Anders

[Johansson]

The spark module had died on me for unknown reasons so I replaced it this morning.

I have also made a stainless mesh intake screen for the engine, I will do some final trimming before fastening it to the bellmouth but you get the idea. I silver soldered it together so I didn´t have to make a sheet metal cage that restricts flow.



I haven´t had time to measure the total area yet and calculate how many times the inducer area it is.



Cheers!
/Anders

[racket]

Hi Anders

That'll stop the big bits ..............certainly looks "open" enough for flow ...........getting closer :-)

Cheers
John