smallest possible combustion chamber?

[notjet]

Hi John,

Ive done some calculations and also incorporated cooling holes. i have not yet calculated the ID and OD etc but i want to get this right before i do the drawing...

What i did for the cooling holes was to deduce cooling hole area for primary from the primary hole area and bottom wall cooling from tertiary area but i was wondering if i should take the area entirely from tertiary instead because im worried that the primary air jets wont penetrate far enough into the flametube. Also i put 70% of cooling area on the outer wall and the remaining 30 on the inner wall

heres what i got so far

Top: 10x 2.5mm

Primary:

Outer tube: 20x 3.2 (2 rows)  Inner tube: Row 1: 10x 2,5mm, Row 2: 10x 3mm  Cooling holes: OT 20x 2mm  IT 20x 1.5

Secondary:

OT: 10x 5.5mm  IT: 10x 5.5mm

Tertiary:

OT: 20x 9mm  IT: 20x 9mm  Cooling: Outer tube 20x 1.5mm

For me the tertiary holes seem abnormally big compared to everything else and also after deducing cooling area from primary it only has about 330mm² left which is even less than the secondary holes (ofcourse the evaps still count tho)

Cheers, Neo

[racket]

Hi Neo

The micro jet engine flametubes don't incorperate "cooling" holes .

I think your Tertiary hole number are wrong 40 holes at 9mm =2545 sq mms = a 57 mm dia hole :-( thats more than your entire alloted hole area for the flametube ................gotta get our maths right ;-)

I really need to see a drawing so that I get an idea of what you intend with your cooling holes .

Cheers
John

[notjet]

Hi John,

My tertiary holes are actually 20x 6mm for the outer and same for the inner tube, i must have messed up typing that very late at night...

I havent really had time to make a proper drawing yet but i can show you the image i have been heavily inspired from while designing, as i do not know yet all it takes to properly design an annular combustion chamber.

(that image is also why i thought the cooling holes would be a neccesity)

Cheers, Neo

[racket]

Hi Neo

There are a multitude of different annular FT designs , it just depends on who is doing the design and what they feel is appropriate .

6mm holes sounds better :-)

Cheers
John

[notjet]

Hi John,

I remember several threads where cooling holes were incorporated, but i dont know exactly when they are neccesary.
I read in your tv84 bike thread that tou used cooling holes because the 0.5 mil stainless ft was a bit too thin but currently you use 1.2 mil and that works fine with cooling in the tertiary area... (11/117 manned flight engine)
I just thought it was of good practise to put some cooling holes in the primary zone too but i may remove those because my primary hole area seems a bit small

Cheers, Neo

[notjet]

I will have some on the top to shield it from radiant heat and also some beneath the tertiary zone to cool the wall where the evap tubes are mounted

[notjet]

Hi John,

here is my new hole data with no longer any primary cooling holes, just some for the top and some for the evap tube wall:

Top: 10x 2mm 10x 1.5mm

Primary OT: 30x 3mm   IT: 30x 2.5mm

Secondary OT: 10x 6mm   IT: 10x 5.5mm

Tertiary OT: 20x 6mm   IT: 10x 8.5

Cooling: (beneath Tertiary) 20x 1.5mm

Drawing will be in tomorow

Cheers, Neo

[racket]

Hi Neo

Generally the Primary endwall of the annular flametube runs cold because of the cooling from the fuel/air impacting it out of the evap tubes , the A/F ratio isn't high enough for combustion to take place , its far too rich a mixture , its only once the Primary air from side wall holes start to mix that combustion takes place ,........... my current engine works differently as I don't have side wall Primary holes as I'm required to have combustion beginning at the front wall because of the extremely short flametube .

Cheers
John

[notjet]

Hi John,

Lots of stuff to learn when designing an annular Flametube ._.

Anyways ill fix that and make a drawing
As soon as that is done and all good ill start the build thread...

Cheers, Neo

[notjet]

Hi John,

Here is my final (we will see about that lol) Flametube design...

I might put the primary holes a bit closer to eachother but i think its good as is now to aid in evaporation

Cheers, Neo

[racket]

Hi Neo

Yep , I'd "compress" the Primary Zone a bit so that you can provide more distance between Secondary and Tertiary holes .

How are you fitting the evap tubes ??

Cheers
John

[notjet]

Hi John,

On the exhaust side of the FT i will have a narrow ring with the evap tube holes and the injector ring

i think ill just weld the tubes in but i dont know yet if i should weld the ring to the outer wall or have it be like a cap that sits loosely so the outer wall can expand

cheers, Neo

[racket]

Hi Neo

Yes, have the fuel ring lightly held in place , theres lotsa different expansions happening .

Cheers
John