Building the JU-02 gas producer

[racket]

Hi Anders

If you have your current thermo active as well , then maybe space the 4 new ones at ~72 degrees apart to get a good coverage of the duct , try and get them as close to the NGV as possible because any "interstage combustion" won't be happening until the gases have slowed down as the annulus area increases approaching the NGV , things are going too fast coming out of the gas producers exducer.

It'll be very interesting to see the results of multiple thermos .

Cheers
John

[Johansson]

Nov 26, 2019 15:43:07 GMT -5 racket said:

Hi Anders

If you have your current thermo active as well , then maybe space the 4 new ones at ~72 degrees apart to get a good coverage of the duct , try and get them as close to the NGV as possible because any "interstage combustion" won't be happening until the gases have slowed down as the annulus area increases approaching the NGV , things are going too fast coming out of the gas producers exducer.

It'll be very interesting to see the results of multiple thermos .

Cheers
John

That I will do! The m5 fittings will be made in mild steel since stainless threads and heat wont make disassembly easy. 🙄

[Johansson]

John,

I´ve been thinking about the temp sensor placement, wouldn´t it be wiser to fit the four identical ones 90 degrees apart and only use them for the temp distribution check?

If I add the Autometer sensor reading I won´t know if a stray reading on it is caused by a hot streak or by the fact that the two different types of sensors read the temps a bit differently.

If the four Ebay sensors show more or less the same value during stationary running I can consider the combustion ok, and then use the Automotive sensor for the road tests.

Cheers!
/Anders

[turboron]

Anders, my experience is that there is a lot of variation in the thermocouple readings measured in the exhaust on a normal functioning engine. You would tend to think that the variation would show up after the nozzle guide vanes and them be mixed out by the rotor. However, significant variation is observed after the gases pass through the rotor. After you determine the hottest location you can place a single thermocouple for your advantage during normal operation.

Thanks, Ron

[turboron]

Anders, my experience is based on aircraft and industrial engines not our DIY units.

Thanks, ron

[racket]

Hi Anders

Yep , I get your point , maybe make all your 4 new thermo mounting pads able to accept your Autometer sensor so that if you find a hot spot you can switch the thermos around to cross check the readings against your Autometer "master"...........I'd like to see you with 5 pickups in the interstage rather than just 4 to get as good a coverage as possible , as Ron said , its normal to have variations in temps between segments of the engines "exhaust" , the smaller those segments are the "better".

Years ago I sorta remember having a chat with Smithy about exhaust temp distribution on the little micro RC engines he worked on and he'd found variations as he "clocked" the jet nozzle temps , the manufacturers seemed to place the thermo in the cooler segment , probably to give the impression their engine ran "better/cooler" than the opposition.

The main reason I'm concerned about your temps is because of the combustion problems I've had with the 12/118, which in the early days , refused to burn extra fuel once I was up to around a 2.5:1 PR , dumping in more fuel didn't get the rotor to accelerate to a higher PR , the extra fuel simply blew out the exhaust .................that extra fuel could possibly have burnt in an interstage duct if the gas velocity had been low enough , maybe producing something like the abberant temps you experienced with the JU-01

Cheers
John

[Johansson]

Hi John,

Hmm, that will be a bit tricky since the Ebay thermos are M5 fittings and the Autometer is an 8mm compression coupling. I understand your concern for eventual combustion problems so I will fit the five thermos evenly around the NGV and see how it goes. I can do some tests with a hot air gun to see if there is a difference in temp reading between the two types of sensors.

One thing that concerns me is the possibility of heat warping of the snug NGV slip joint if I start welding thermo bungs next to it.

Cheers!
/Anders

[Johansson]

Dec 3, 2019 7:16:34 GMT -5 turboron said:

Anders, my experience is that there is a lot of variation in the thermocouple readings measured in the exhaust on a normal functioning engine. You would tend to think that the variation would show up after the nozzle guide vanes and them be mixed out by the rotor. However, significant variation is observed after the gases pass through the rotor. After you determine the hottest location you can place a single thermocouple for your advantage during normal operation.

Thanks, Ron

Good pointer Ron!

I don´t want to measure temps in a cool spot since that might trick me into pushing the engine too far and damage it.

Cheers!
/Anders

[racket]

Hi Anders

Can you have the slipjoint parts mated together when you weld ??

Maybe only tack weld the bungs and have a neat hole for the thermo to slip through, the small quantity of leakage shouldn't be a problem , weld warpage is a problem but I found the slipjoint between my jetpipe and scroll was still OK after welding when I had a "bung" in it to keep it "round" .

Another thought ............could you drill and tap the 5 mm holes in the NGV , theres lowish static pressure in the interstage so just a few threads will hold .

Cheers
John

[Johansson]

Dec 3, 2019 18:29:13 GMT -5 racket said:

Hi Anders

Can you have the slipjoint parts mated together when you weld ??

Maybe only tack weld the bungs and have a neat hole for the thermo to slip through, the small quantity of leakage shouldn't be a problem , weld warpage is a problem but I found the slipjoint between my jetpipe and scroll was still OK after welding when I had a "bung" in it to keep it "round" .

Another thought ............could you drill and tap the 5 mm holes in the NGV , theres lowish static pressure in the interstage so just a few threads will hold .

Cheers
John

Hi John,

Your second thought was an excellent one! The small M5 sensors should be possible to thread directly into the interstage wall without the need for a welded bung.

The Autometer sensor has already been welded in so I will leave it where it is and space the four Ebay sensors evenly around it.

Cheers!
/Anders

[racket]

Sounds good to me :-)

[racket]

Hi Anders

What fuel did you use in the JU-01 ??

Will you be using the same with this engine ??

Just a thought ............maybe try a similar mix to my 12/118 engine with 2 Parts unleaded petrol to 1 Part kero as I feel it helped with the combustion in our very short flametubes.

Cheers
John

[Johansson]

Hi John,

I used pure aviation kerosene in JU-01, and so far I have used the same in JU-02. Perhaps it would have been a good idea to blend in some petrol for JU-01 even though it would have ruined the nice smell.

Since I will be sitting on the bike I want to run with the least flammable fuel as possible, getting caught in a fireball if a hose breaks is something I want to avoid. I will keep running JU-02 on Jet-A1 and if the temps indicate a combustion problem I will try a kero/petrol mix to see it it improves things.

Cheers!
/Anders

[Johansson]

A couple of days ago I drilled and threaded the interstage duct for the M5 temp sensors.



Here you can see the slip joint on the freepower NGV, I was just about to lift the drive train into the bike chassis.



And here is a better view of the other half of the slip joint, this will be a great improvement since I can firmly mount both the gas producer and the drive train. On JU-01 I didn have a slip joint and had to make the gas producer brackets so they could slide axially on the bike frame tubes when the interstage duct expands from the heat.



After some back breaking moves and some shimming of the gearbox mounts I had the whole engine package aligned in the bike chassis.



I also changed the rear chain sprocket to a smaller one to get the gearbox revs down as much as possible, now I will reach aprox. 360km/h with 30.000rpm on the power turbine wheel which is within the rev limits.



Cheers!
/Anders

[racket]

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