The One Man Turbofan

[monty]

John,

I'm starting to work on the combustor. Any software or rules of thumb? Jet Specs isn't really suitable since I plan to use a annular type.

Monty

[racket]

Hi Monty

Thats great news :-)

COPY COPY COPY your flametube .

As long as your cross sectional area is 3 times inducer area, with an inducer's worth of holes and you have at least a 1.5:1 length/width ratio for the annulus , things should work , same percentage division of holes.

Cheers
John

[madpatty]

Hi Monty.
I was just wondering how’s the rotor dynamics gonna look like for this modified rotor especially with an overhung gear and single brass bearing between the compressor and turbine.

What are your thoughts on that?

Regards
Patty

[monty]

Hi Patty,

My thoughts are:

It's better than a full overhung design, which I considered, but rejected because the turbine quill shaft isn't stiff enough. Though the compressor I eventually settled on is probably beefy enough that I could drill out the center bore for the larger unmodified turbine quill and perhaps get away with it. There would need to be an intermediate shaft/spacer that slides over the quill between the two bearings. The tension on the stack would be critical to maintain structural integrity. There are so many potential gotchas with machining this after the fact and getting everything essentially perfect - I just decided not to go there. If the current design doesn't work I might though. A fully overhung design would certainly solve a LOT of plumbing issues.

There is a ceramic deep groove ball that takes the thrust and front radial loads. The forward bearing is in the cool section, and the rear brass bushing is in the hot section. The rotor assembly is stiffer than the original, because the compressor adds to the stiffness of the shaft. The second mode should be at an even higher frequency than the original because of the added stiffness, and less overhung weight. The mode I'm concerned about is whirl about the ball race. I'm counting on the damping from the bushing and meticulous balancing to take care of that. Unfortunately there are too many unknown variables for me to do a good job calculating this.

At some point you have to shoot the engineer, build the silly thing and see what happens....

On a side note, I can't log into JATO using anything but Chrome. I get all kinds of log in errors I can't figure out. Anybody else had this problem?

Monty

[monty]

Aug 31, 2021 19:21:53 GMT -5 racket said:

Hi Monty

Thats great news :-)

COPY COPY COPY your flametube .

As long as your cross sectional area is 3 times inducer area, with an inducer's worth of holes and you have at least a 1.5:1 length/width ratio for the annulus , things should work , same percentage division of holes.

Cheers
John

Thanks John,

How do you account for the vaporizer tube area for primary air? I'm assuming there is some correction factor for fuel blockage. I have a combustor design program for full sized stuff, but we are operating so far outside the envelope from the big engines......it isn't much help. Too many assumptions in the code that I can't customize.

Monty

[racket]

Hi Monty

~10-12% of total hole area for the tube bores ( ~1/3rd of Primary air) , and heating surface area of tubes at 6 inducer areas , not always an easy combination to obtain ..............no correction factor for fuel blockage .

Do you have a general layout yet ??

Cheers
John

[monty]

Sept 1, 2021 16:44:22 GMT -5 racket said:

Hi Monty

~10-12% of total hole area for the tube bores ( ~1/3rd of Primary air) , and heating surface area of tubes at 6 inducer areas , not always an easy combination to obtain ..............no correction factor for fuel blockage .

Do you have a general layout yet ??

Cheers
John

John,

General layout:









I sized all the areas like you suggested. 14 vaporizer tubes.

The length is a bit short, but I have room to make it 5X length. I'm pushing the 3X inducer area for the annulus. It's about 5% on the small size. I can make it bigger, but I'm not sure 5% is worth all the re-design. It was previously sized using my full size engine software, and the number of vaporizers was 12. I made the change to 14. Not sure on the size and location of all the holes, and how to handle cooling air around the hot bits.

Monty

[racket]

Hi Monty

Length is more than adequate :-)

5% under should be OK as long as you haven't compromised the flow space around the flametube for air to get to all the holes , I contemplated using a reverse flow combustor on my latest engine whilst using an original CHRA , but because of the need for a 5" exhaust through the centre of the combustor it meant a larger casing that my 12" comp stage castings............compromises :-(

Have you considered what the Solar T62 does for its cooling ?

Cheers
John

[monty]

Sept 3, 2021 17:20:42 GMT -5 racket said:

Hi Monty

Length is more than adequate :-)

5% under should be OK as long as you haven't compromised the flow space around the flametube for air to get to all the holes , I contemplated using a reverse flow combustor on my latest engine whilst using an original CHRA , but because of the need for a 5" exhaust through the centre of the combustor it meant a larger casing that my 12" comp stage castings............compromises :-(

Have you considered what the Solar T62 does for its cooling ?

Cheers
John

John,

I haven't considered what Solar does, but I'm all ears!

I've also considered arranging the primary and secondary holes so they create self reinforcing vortices around the primary combustion areas. This swirl would help with mixing. 

Monty

[racket]

Hi Monty

The T62 is very basic , only 6 injectors , you probably don't need 14 because you have "length" in your flametube whereas with our turbo based engines our annular flametubes are very short so we need to "compress" the time/distance of combustion which requires us to divide our annulus into many smaller portions so that the L/W ratio is improved , eg , with 18 injectors around a mean diameter of say 10 inches it makes them only ~1.7" wide and with a L/W ratio closer to 2 rather than 1.5 if we only had a dozen injection points.

The T62 NGV and exducer shroud are a single piece with no real "cooling" additions .

It might pay you to get hold of manual or some video of a disassembly as you're engine is "similar??"

Cheers
John

[monty]

Sept 3, 2021 20:01:10 GMT -5 racket said:

Hi Monty

The T62 is very basic , only 6 injectors , you probably don't need 14 because you have "length" in your flametube whereas with our turbo based engines our annular flametubes are very short so we need to "compress" the time/distance of combustion which requires us to divide our annulus into many smaller portions so that the L/W ratio is improved , eg , with 18 injectors around a mean diameter of say 10 inches it makes them only ~1.7" wide and with a L/W ratio closer to 2 rather than 1.5 if we only had a dozen injection points.

The T62 NGV and exducer shroud are a single piece with no real "cooling" additions .

It might pay you to get hold of manual or some video of a disassembly as you're engine is "similar??"

Cheers
John

John,

Looks like the Solar uses "macro" swirl to produce toroidal flow. 6 high pressure injectors arranged tangentially. Though I could do something like that, I would rather copy what you guys have been doing for a couple reasons. 

With smaller combustion zones, I think turn down performance will be better. Anecdotally you guys have way better throttle response with the smaller vaporizer engines than you get with something like the Solar design. I also want to use EFI pumps and not a high pressure pump. 

I want to reduce the length. I'm not happy with how long my current design is. I'm thinking I may compromise and go with 12 vaporizers. 12 is on the low end. 10% of total hole area gives 12.8 tubes. 12% gives 15ish. I need an even number for my vortex idea to work. If I go with 12, I think I can make a die to bend the vaporizers into a U shape. That would be better than chopping and welding all the tubes; something I'm not looking forward to. 

I am going to copy a few things from the Solar design around the NGV. Then copy what you have done with the vaporizers. I may try my primary and secondary swirl idea and see what happens. The nice thing about an overhung design is I can spend a lot of time fiddling with the combustor without taking the whole engine down.

How short have you managed to make your can?

Monty

[turbotom]

Monty -

the T-62T-32 utilizes six air blast nozzles, arranged at an angle to introduce macroscopic swirl. The configuration of the air blast nozzles as a venturi achieves close to sonic flow speed at the throat with only moderate pressure drop accross the liner. Fuel is introduced at very low velocity just upstream the throat. The very high difference of velocity between the air and the fuel produces a very finely atomized fuel mist. The disadvantage of this fuel atomization method is that you cannot directly ignite such a burner, you need a separate ignition burner to light up the whole thing and to "help" the starter to reach about 30% of engine rpm so there's enough pressure across the liner to make the air blast atomization work. The angled arrangement of the air blast nozzles distributes the flame around the annulus of the combustor so even though rather few burners are utilized, the temperature distribution is fairly even. Most of the primary air flows through the air blast nozzles, other holes in the primary zone of the liner mainly serve the purpose of wall cooling. The combustor is really very simple but performs well.

[finiteparts]

Monty,

I have some photos photos of the vaporizer variant of the T62 here:

jetandturbineowners.proboards.com/post/9810/thread

..starts at the bottom of page one.

There are quite a few variants of the basic T62 and some of them use vaporizers, air-blast atomizers or pressure-swirl atomizers.

I am a fan of using the combustor that hangs aft of the NGVs, so that you can size it properly and not just to whatever space you happen to get between the compressor and turbine,  So I really like your design.  Also, the mitered "walking stick" vaporizers are very good at breaking up the fuel as it travels through,  The sharp corners provide very effective separations that help to rapidly process more fuel,  Snecma and Rolls Royce both talk about this in various technical papers and patents, so don't discount that design approach right out.   It might be good to compare and contrast them with the T62 arrangement of others.

Good luck!

Chris

[racket]

Hi Monty

The TF15M turb wheel drawing


Cheers
John

[monty]

Thanks for the info guys! After looking at things, I made some changes. Not quite done with everything, but I feel better about the proportions.





Now I have to start thinking about starting...I need kerosene start. No gas. Opinions on the best methods?

This new larger turbine you guys have dug up is causing me all kinds of angst. The smaller turbine was always the limiting factor. 

Monty