Building the JU-02 gas producer

[racket]

Hi Anders

Looks like Monty doesn't owe you a beer :-(

The second test was virtually the same as the first one except the torque required was a tad less , the initial 25 kgs pull at 11 inches was rock solid , but with the 22 inch arm I only got to 14 kgs before movement , maybe my poor old nut and shaft threads are getting "soft"..

There was also a variation in where the slippage occured , at the front under the nut was the same , but at the rear it was the oil slinger to shaft face that slipped rather than seal holder to "comp" .

I also did a torque wrench test of tightening the nut using Loctite for lube and it was ~65 ft lbs to get the required 135 degrees .

But it looks like no matter how the shaft is assembled you've got a sufficient buffer between the torque required and torque resistance available , plus as the comp warms up it'll expand more than the steel shaft so extra clamping power applied.

Cheers
John

[Johansson]

Hi John,

I have just finished measuring the NGV area, it is -18c outside and only 5c here in the workshop so I wont bother writing a novel on the cell phone with my stiff fingers.

I got the total NGV area to 3383.1mm2.

Will check the comp housing more closely now, but it looks like the comp has had more contact on one side.

Cheers!
/Anders

[racket]

Hi Anders

Thanks for that , it'll give me something to work on :-)

Gotta go and pickup my balanced rotor this afternoon , hope to get the 12/118 back together before Christmas

Cheers
John

[racket]

Hi Anders

My calcs for your engine had required NGV throat area at 3182 sq mms , your 3383 sq mms is only ~6% extra , we can live with that :-)

The slightly extra mass flow might be at a bit lower comp efficiency ,and you might need to increae the jet nozzle size by a couple of mms to keep temps down , you're already at ~920 C for the T I T , any higher Pressure Ratio and you'll be getting closer to 1,000 C ....................she must have been sounding rather impressive just before the comp rub .

Cheers
John

[Johansson]

Hi John,

I took a good look on the wear marks in the compressor cover, it sure looks like the comp rubbed more on one side. It might be that the castings have settled in a bit during the runs, I´ll focus on the tight side when I fix the clearance later. 0.4mm it is then, should be plenty as long as there are no tight spots like there might have been now.

Dec 13, 2018 16:06:34 GMT -5 racket said:

Hi Anders

Looks like Monty doesn't owe you a beer :-(

The second test was virtually the same as the first one except the torque required was a tad less , the initial 25 kgs pull at 11 inches was rock solid , but with the 22 inch arm I only got to 14 kgs before movement , maybe my poor old nut and shaft threads are getting "soft"..

There was also a variation in where the slippage occured , at the front under the nut was the same , but at the rear it was the oil slinger to shaft face that slipped rather than seal holder to "comp".

I also did a torque wrench test of tightening the nut using Loctite for lube and it was ~65 ft lbs to get the required 135 degrees .

But it looks like no matter how the shaft is assembled you've got a sufficient buffer between the torque required and torque resistance available , plus as the comp warms up it'll expand more than the steel shaft so extra clamping power applied.

Cheers
John

Great news (even if it cost me a cold one...) since I won´t have to worry about not having the bearings perfectly clean during assembly, in fact I will put a coating of oil on the parts since that seems to give the best torque resistance.

Dec 13, 2018 20:01:50 GMT -5 racket said:

Hi Anders

My calcs for your engine had required NGV throat area at 3182 sq mms , your 3383 sq mms is only ~6% extra , we can live with that :-)

The slightly extra mass flow might be at a bit lower comp efficiency ,and you might need to increae the jet nozzle size by a couple of mms to keep temps down , you're already at ~920 C for the T I T , any higher Pressure Ratio and you'll be getting closer to 1,000 C ....................she must have been sounding rather impressive just before the comp rub .

Cheers
John

I´ll open up the nozzle a bit then, here are some pics of the internals. The bottom evaps seems to have run hotter than the top ones as can be seen in the pics.

Bottom ones:



Top ones:



Ejection marks in the combustor lid:



Cheers!
/Anders

[Johansson]

I picked up the 12v-24v converter today, for some reason I got the larger 1200w model but that is only good since I´ll have a bit more margin. I´ll hook it up to the 12v supply and test the oil pump this weekend!



Cheers!
/Anders

[BFTO]

Looks heavy and bulky for a bike? a 6S (22,2V) lipo at 5ah is around 800gram and quite small, needs to be recharged between runs tho.

[nco]

OMG I can't believe it
So how much thrust this engine?
Congratulations sir👍👍👍👍

[elventu]

Dec 13, 2018 8:47:12 GMT -5 Johansson said:

Dec 13, 2018 7:37:39 GMT -5 CH3NO2 said:

Could an ablative liner for the compressor housing be as simple as several coats of spray on varnish?

I was thinking about that too, a generous 1mm clearance and then a thick layer of abrasive coating so that the compressor can sort the clearance out itself. That would be neat!

A car tuner that I had to do with used this system on the old style turbochargers he put on some cars.
I remember that he give us a couple of compressor housing to be machined on the coupling surface to the flange (after precise rebuild with 360° thrust bearing).
We reduced the clearance between comp.wheel and housing, and after that he paint the internal part of the housing with, if I remember well with the type of spray blue-transparent paint it is used to cover the plate when it have to be "traced" in traditional mechanical work.
It is a kind of paint that is "fragile" instead of being "plastic", in case of contact with the compressor wheel.

I remember that his modified turbo has good performance, his Lancia Delta Evoluzione was one of the best racing car of my zone.

Hope this can be useful!

Davide

[Johansson]

Dec 14, 2018 8:13:23 GMT -5 BFTO said:

Looks heavy and bulky for a bike? a 6S (22,2V) lipo at 5ah is around 800gram and quite small, needs to be recharged between runs tho.

This one is a bit larger than the 1000w one I ordered, but I don´t mind that it is a bit large. Better that than having a second battery that needs to be charged between runs.

[Johansson]

Dec 14, 2018 8:39:34 GMT -5 nco said:

OMG I can't believe it
So how much thrust this engine?
Congratulations sir👍👍👍👍

Thank you! I don´t remember the calculated max thrust but 700-800N I think.

Dec 14, 2018 8:45:21 GMT -5 elventu said:

Dec 13, 2018 8:47:12 GMT -5 Johansson said:

I was thinking about that too, a generous 1mm clearance and then a thick layer of abrasive coating so that the compressor can sort the clearance out itself. That would be neat!

A car tuner that I had to do with used this system on the old style turbochargers he put on some cars.
I remember that he give us a couple of compressor housing to be machined on the coupling surface to the flange (after precise rebuild with 360° thrust bearing).
We reduced the clearance between comp.wheel and housing, and after that he paint the internal part of the housing with, if I remember well with the type of spray blue-transparent paint it is used to cover the plate when it have to be "traced" in traditional mechanical work.
It is a kind of paint that is "fragile" instead of being "plastic", in case of contact with the compressor wheel.

I remember that his modified turbo has good performance, his Lancia Delta Evoluzione was one of the best racing car of my zone.

Hope this can be useful!

Davide

Thanks Davide for the info, I guess that with a properly trimmed in compressor cover there is no need for an abrasive coating but still it would be fun to try and one could run tighter clearances when knowing that a rub won´t damage the compressor.

Cheers!
/Anders

[CH3NO2]

Epoxy can be made sandable and with a low density by blending with glass microspheres/microballons.
youtu.be/6LeCeynaA_E

When mixed properly into epoxy the cured material resembles balsa-wood.
Mix epoxy resins and spread it out thin on a hard flat surface with a trowel. Dust it with glass microspheres, mix it up with a trowel and spread it out flat again for addition of more glass microspheres. Repeat as needed for the density and consistency you want.

[turboron]

Anders, I support John's call for a 0.5mm (0.0197")clearance between the impeller and the shroud. Any more than that will be too severe an impact on efficiency which will drive up you turbine inlet temperature. I have experience with abradable coatings from aircraft/helicopter gas turbines and they are difficult to get right and require a development program. You should not consider an abradable coating for your one off application with a right hand thread. I do suggest you lap the impeller to the shroud to eliminate high spots and improve efficiency. My experience with lapping is Ti impeller to Al shroud so you will need to investigate Al to Al lapping materials and methods.

Thanks, Ron

[racket]

Hi Anders

If the comp has rubbed on one side of the cover then you will need to set the diffuser wall up on a trued up "shaft tunnel" jig in the lathe to check the diffuser vane face to see if its running true, without the diffuser vanes all being true to the shaft tunnel face the front cover will be a nightmare to "massage" so that the clearances are even around the wheel

Cheers
John

[Johansson]

I´ll bolt the diffuser to the shaft tunnel and fit it in the lathe.