"Fat Boy" 12/118 thrust engine

[enginewhisperer]

It definitely picked up some output torque when the bleed valve closed! (which means it's doing its job of bleeding off a decent amount of the flow)

Was the oscillation in the exhaust duct due to turbulence, or a mechanical vibration?

[racket]

Hi Guys

Yep , had a couple of "boys" here today , thought they should start their holidays with a bit of blokey stuff before going fishing :-)

The torque ended up at ~16 kgs on the spring balance , so 35 lbs at the end of a 2 foot arm , so 70 ft lbs of torque at the pinion , not quite up to my hoped for 80+ lbs but considering the less than ideal turb wheel blading for stalled work , it'll do , the arm was moving nicely as the power was increased .

70 ft lbs going into the 4.3636:1 gearbox will produce >300 ft lbs of output torque , with a 2:1 chain redux that increases to 600 ft lbs at the kart axle and with a ~11 inch tyre that equates to ~1300 lbs of
thrust between tyre and road ...................LOL, good luck to the driver .

The water injection seemed to work OK, coming in at ~1.5 Bar , but there was still some "colour" at the wheel at full throttle , pump activation was tested prior to spoolup by shorting out across the P2 pressure switch .

I think theres very little worth in trying more testing of the setup with a stalled wheel, my thought are that initial takeoff is done with maybe ~2 Bar of P2 with water injection activated ,and once underway the throttle can be floored and ~2.8 Bar be used sparingly for short periods of several seconds .

Closing the bleed valve scared the crap out of me , the sudden increase in "violence" caught me by surprise .

The exhaust pipe made from 0.5mm thickness stainless and held in place with only 4 stainless pop rivets was making some strange shapes as the power was increased , it sent a vibration through the entire test stand , it will need at least another 8 rivets to provide some stability , and possibly a cone shroud over the turb disc in the jetpipe to create a diffuser exhaust and more power output

The butterfly valve will need a stronger spring arrangement or a push/pull cabling arrangement to prevent the valve from sticking shut.

The boys enjoyed themselves and I got the test done during a small window of safe weather conditions , we're back to catastrophic bushfire conditions tomorrow .

Development finished :-)

Cheers
John

[Sweetenough]

Hi John,
Great work, nice run! Congratulations!
Also great fun to see the preparations around the start as well.
Kind regards
Thomas

[turboron]

John, excellent development program. Well thought out solutions to the problems encountered. The clipped turbine experience was a "dead end". Lots of "dead ends" in development. A job well done.

Thanks, Ron

[slittlewing]

Excellent work - a huge amount of time and skill in making that freepower! You even made a mobile testing trailer!

Cheers

Scott

[monty]

Great to see it run John! Thanks for keeping the updates and inspiration going.

Monty

[racket]

Thanks guys :-)

And one more vid of an old fart waffling on in his shed www.youtube.com/watch?v=YNsJ2Y3NP04.

Cheers
John

[enginewhisperer]

I might have some suitable push pull cable bits kicking around - from a motorcycle exhaust power valve setup.

[Johansson]

How I wish we lived closer to each other so I could drop by and see the engine in real life and shake your hand for all the help youve given me over the years.

[stoffe64]

Congratulations John to a very Nice engine,alot of hard work payed out,be proud ,be happy......hell I have not built any engine yet....I must get your energy,but this was a bit energy giving, i started to Think about my build Again...too much diversions it has been around.....Happy New year to you as well and thank you for being a mentor and help to many newcommers(including me)över the years....I second Anders whish,i would also like to shake your hand,thank you being around my friend!
Cheers/Stephan

[finiteparts]

Good to see such a long run on your engine. Congrats!

That exhaust duct is doing some interesting flapping. I would bet money that it is due to the large amount of swirl that you are imposing in the duct via the stalled turbine. The long flow path due to the swirl will no doubt cause quite a bit of scrubbing on the duct wall and with it being so thin, you essentially have a cylindrical flag flapping in the breeze. ha! I would install a doubler ring at the exit of the duct to give it a touch of structural ability to hold it's circular shape. If you could make a cylindrical l-shaped ring, that would really increase the duct exit stiffness due to the increased section modulus of the vertical part of the ring, but at minimum, a doubler ring would help.

So the water injection didn't help, the turbine was still glowing?

I agree that the next test should not be a stalled turbine and should allow it to rotate. If you still experience high temps at the PT, you could think about trimming the trailing edges of the NGV section slightly to open up the PT through flow area. Trimming NGVs is actually commonly reported in the older turbojet literature.

Did you get a shot of the compressor pressure gauge when you shut the wastegate? It seemed pretty sudden and I would like to see how the compressor behaved with a sudden back pressuring pulse. It didn't appear to experience any significant surge (or at least I didn't hear it) when it occurred, so that is something good, telling you that you have a decent surge margin on your operating line.

Thanks for posting and can't wait to see the next stage of testing.

Chris

[racket]

Hi Chris

Yep , some extra work on the exhaust pipe required , it was only a quick addition to get the gases past me when doing a spoolup , not much though/time put into it .

The water injection certainly helped and kept "colour" at bay other than at absolute max power which is probably only going to be used once the wheel is spinning and the impact temps are lower .

Theres undoubtedly an enormous amount of turbulence at the inlet of a stalled wheel when the blading isn't designed for smooth entry other than at 95%+ N2, my thoughts are that the gases are "bunching up" and then flowing out of the wheel at much higher velocities ( poor description) , for our vehicle use , an impulse type wheel might be a better choice , with the inlet side of the blading designed to better "catch" the gases at low blade speeds , with a smooth entry theres going to be better gas deflection and a higher stall torque being produced making initial vehicle acceleration better, with my current setup my guess is that power/torque will increase once the wheel is spinning at >10,000 rpm

Idealy the test stand need reconfiguring with all the gauges together so that a single fixed camera could view them , but its time for me to call it quits on this engine , it needs to be fitted to a vehicle and dyno tested through the wheels so that the freepower can be operated within its designed range which will most likely produce completely different results to what I'm getting .

Cheers
John

[racket]

Hi Ron

"The clipped wheel"..........now I might need to sit and think on that one a bit , I need to go through the Build Thread and check on where I was in the development and if it was the "problem" or just a "victim" of other contributing factors , similarly with the removal of the comp extended tip and the addition of the surge slot , the combustion issues could have over ridden the clipping .............something to ponder over.

Cheers
John

[monty]

Jan 3, 2020 3:23:40 GMT -5 Johansson said:

How I wish we lived closer to each other so I could drop by and see the engine in real life and shake your hand for all the help youve given me over the years.

We need some kind of model engineering Valhalla...

[racket]

Hi Guys

Was just watching the vid again www.youtube.com/watch?v=q7aNAhvMAao for pointers/ideas/explanations and I noticed at 9:37 whilst cooling down the engine, and with some oil bypassing the turb seal and producing lotsa smoke ( I really need a big scavenge pump) , that the "wastegate" was passing as much smoke as the exhaust pipe despite the wastegate only having around a quarter the area of the wheels "exducer" throats , it appears as though the wheel design is making it very difficult for gases to pass through even at the low speeds of a leaf blower airflow .............I now kinda understand why there was was such a large increase in torque when I closed the wastegate.

Every time I go though the vids I see something new that helps with understanding what went on :-)

Cheers
John