"Fat Boy" 12/118 thrust engine

[racket]

Hi Anders

Unfortunately nope

The flametube looks like its burning more from the secondary hole and rearwards



My latest thought is to construct an auxiliary gas manifold for the front of the flametube and inject the gas through those already "bent" holes in a tangential fashion to create more swirl within the flametube at the Primary Zone , the LPG gas will also ignite/burn much faster and over a greater F/A ratio and hopefully as it'll be discharging through the outflow from the evaps create a scenario for combustion to begin at the evap mouth rather than once the fuel/air mix has hit the front wall, turned around, and started to travel back along the flametube.

LOL, I really don't know what I'm doing , I'm desperate .

Cheers
John

[Johansson]

A run on propane sounds like a good next step, at least it should show if the problem is connected to late evaporation of the liquid fuel.

[racket]

Yeh , it'll hopefully do something , if it doesn't then I'll just have to accept defeat and make major changes to the engine which unfortunately will mean another years work , but eventually I'll get that comp wheel up to some decent pressures .

[jetjeff]

Hi John,

You could build a flame tube that sits behind the turbine wheel similar to the Swedish PAL engine (some info on this engine is in the Kamps book).

Granted a lot of work, but better than starting from scratch.

Jeff

[miuge]

Just throwing ideas.. how does the air deflector effect to burning zone? Could it disturb outer surface air flow at the primary zone? How does the inner surface look like, similar heat pattern?
I really wish to see it running properly, mounted on a free power wheel

[turboreno]

John, good time to get a cup of coffee and look for the simple answer. One approach might be to replace the clipped TV94 turbine wheel with an Allison Model 250 axial turbine nozzle and wheel. You seem to have a good source for the Allison turbine goodies.

Thanks, Ron

[racket]

Hi Jeff

Yes, a lot of work to remodel to a rear flametube :-(

If the proposed mods don't work then its most likely the miss match of comp/turb , I really was getting a bit greedy trying to use such a big inducer on a TV94 turb wheel, LOL,...... at least I won't die wondering if it was possible ;-)

Cheers
John

[racket]

Hi Miuge

I think I'm OK with the deflector , theres a fair bit of distance to the first holes and there is some combustion happening from the colouration of the flametube , but maybe not fast enough combustion.

A number of the RC micro jet engines had tangential "swirl jets" fitted to their flametube primary zones to promote better combustion , the proposed LPG gas injection through 9 tangential injectors should do the same job of creating swirl within the flametube as well as introducing a highly combustible fuel that should speed up the kero combustion ...............LOL , maybe :-)

Cheers
John

[racket]

Hi Ron

If only I could fit an Allison wheel , but their diameters are too big for the flow area available , excessive turb tip speeds would result :-(

The 2nd stage C20 wheel would be getting close to the flow size but its already the same diameter as the comp , the C30 2nd stage would be about ideal but its too big in diameter , heh heh , I've been trying to use those wheels for years without success , though there probably are some low trim billet "supercharger" comp wheels that might be getting closer to a match .

Cheers
John

[gtbph]

Hi John,

What do you think about reducing the compressor exducer diameter?
This would not require much redesigning, and I hope it could make the components work better together, because it would produce less pressure and require less power. To bring the air density up again, you could reduce the firing temperature. Of course it would also mean less thrust. (don't know if that's correct, just thinking)
But I hope the switch to propane will be enough to make it work.

Cheers, Alain

[smithy1]

Hi John,

Just thinking out loud here....but, before you do any major changes, could you try ~20-25% petrol mix in the fuel to help speed up the combustion a tad and bring it a little further up the flametube, probably won't help much but may be worth a try.

I have C20B 3rd & 4th wheels here too if you need 'em for future experiments..!

Cheers,
Smithy.

[racket]

Hi Alain

Unfortunately theres not a lot of "tip" on this wheel that could be removed , inducer 117.5 mm, exducer 151 mm with extended tip to 163 mm , thats a rather large 60.5 Trim wheel at the 151 mm dia , and a 52 Trim even at the extremes of the extended tip , if the wheel was say a 42 Trim then it'd be possible to remove some material at the exducer , but at a 60 Trim the inducer tip speeds are already going to ~Mach 1.3 even at relatively modest P2s :-(

LOL, not many options with this engine .

Cheers
John

[racket]

Hi Smithy

Yep , I'll take your advice and add some petrol to the kero next time , every little bit will help :-)

Cheers
John

[turboron]

John, a simple solution may be to suck on the exhaust. Consider an electric motor driven blower to pull the exhaust sub-atmospheric which will increase the expansion ratio and therefore the turbine power.

Thanks, Ron

[racket]

Hi Ron

LOL , that would need to be a powerful blower/sucker of >100 HP just to produce an extra half a pressure ratio :-(

Cheers
John