Flame tube size.

[nnhalo]

Im rebuilding my flame tube as my last one was definitly not the best for my turbo. In jet specs my inducer sizes calls for a 6in flame tube which means a 7 in housing. well its rather tricky finding the 7in pipe for a decent price and not needing a whole lot. however i have 5 in pipe and 6 in pipe i was curious to know if i could get away with a smaller diameter flame tube if i make it longer? and if so aprx how much longer?
the inducer is 56 mm wide using a holset hx35w turbo.

[racket]

A 5" dia flametube inside a 6" outer can will be OK for a 56mm inducered compressor wheel , we need a minimum of 3 times the inducer area for our flametube cross sectional area .

If you use a 5" FT you only need to make it 12 -15 inches long ................once you go past that ~3:1 ratio of FT length to FT dia theres nothing to be gained by any more length , if anything there will be extra losses .

The critical part of the flametube is cross sectional area , we CANNOT compensate by increasing length .

Cheers
John

[nnhalo]

Thanks john will let yall know how it turns out

[CH3NO2]

The 3:1 area ratio suggests to me the criteria for flame can flow area is a matter of velocity but is this minimum area ratio fixed in all cases or can it change with combustion chamber geometry?
Can
Annular
Rectangular

I'm wondering is there a total flow area to total surface area ratio effect?

Lets use a hypothetical comparison for example.
A baseline single 7.1" diameter flame can of 40 square inches flow area.
Vs
A rectangular combustion chamber (of high aspect ratio) also with 40 square inches. Say a 2" X 20" combustion chamber.

Assuming we stay above the minimum critical area for the flame holder to sustain the flame, how will this change of geometry affect flame length, combustion efficiency and zone 3 coolant air jet penetration?

Are chamber length and area requirements affected by chamber geometry or aspect ratio?
How about the use of downstream swirlers or turbulators?

Thanks,
Tony

[racket]

Hi Tony

A single large 7.1" diameter round flametube can be serviced by a single fuel spray nozzle , a 2 X 20" rectangular would need at least 10 fuel injection points , but it could be made only 6 inches long whereas the 7.1 incher would need to be a lot longer .

Get yourself a copy of Lefebvre's 1983 edition www.amazon.com/Gas-Turbine-Combustion-Arthur-Lefebvre/dp/0891168966/ref=sr_1_3?s=books&ie=UTF8&qid=1492294929&sr=1-3&keywords=gas+turbine+combustion

Cheers
John

[CH3NO2]

Very cool. I just got a copy of that book in a couple days ago.
I'll check it out.

Thank you!

[racket]

Its the "bible" regarding combustion thats applicable to our needs , more modern editions get too complicated.