smallest possible combustion chamber?

[notjet]

Hi guys,

Just aksing for some advice, im planning to build a 50mm inducered jet which has to be as compact as possible and was wondering what ideas you guys have to make the combustion chamber smaller.

I calculated the FT size with jetspecs and it said 150mm diameter and 300mm lenght. now i was wondering if it is possible to make that any smaller and how

Cheers, Neo

[racket]

It is possible to make it considerably smaller but it requires more sophistication of fuel and air delivery and mixing , the whole point of Jetspecs is that it will produce a working engine first time no matter how crudely its made .

What fuel do you consider using??

[notjet]

I want to use a diesel/gas mix with evap tubes

[racket]

The smallest possible combustor would then look like one from an RC jet engine .

[notjet]

so like this?
How do i calculate the right size for this? jetspecs is designed for the sore thumb type right?

[racket]

50 mm inducer = 1963 sq mms , multiply by 3 = 5890 sq mms , this is the cross sectional area of the annular flametube "ring" .

You haven't indicated if this is being used on a turbocharger or as part of a micro jet engine , the application will change some parameters .

[notjet]

Im planning to use a turbocharger to make the build a little easier so i can step up to more complicated stuff later

[notjet]

Wait scrap that i better stop hassling you and get a design done, the ask questions that make sense

[racket]

If on a turbo , the usual shaft tunnel allowances for the diameter of the inner wall can be removed from the required airflow area .

Yep , a design would help :-)

[notjet]

Hi,
When designing an annular combustion chamber without the inner wall for the shaft tunnel, can i place primary holes in the top sheet?

I read about this on a thread in here but ut had alot if pictures explaining everything and sadly those suffered from link rot...
I do remember that the holes had to be between the evap tubes, and the cross section still 3x, and that a large amount of holes are needed but apart from that its pretty vague without the pictures...

Cheers, Neo

[racket]

Hi Neo

An annular flametube without the inner wall , is a normal can flametube, which can have a portion ( ~1/3rd) of the Primary hole area in its end .

But not having the inner wall means a larger combustor , the inner wall allows air to enter from more positions which can speed up combustion

Cheers
John

[notjet]

Hi John,

LOL i should have understood that alot earlier...
I guess i have to make the hole area in the inner wall about the same as the inner wall opening cross section? (Where the shaft tunnel would have been) also is there any rule on how big i have to make the inner wall opening?

Cheers, Neo

[racket]

Hi Neo

The inner wall "cavity" needs to have a cross sectional area of at least 1.5 times the area of the holes its feeding .

May I suggest you draw something up so that its easier to comment on

Cheers
John

[notjet]

Hi John,

Here is a drawing of a can style combustor since after doing some tests i found out that the annular would be too "fat" for my use so i just tried to shorten the can style FT as you can see here:

sadly it didnt scan so well but ill see later if there is anything i can do about that...

Cheers, Neo

[notjet]

oh i just realized i didnt include data for the evaps, but ill have to do some more calculations for that if im even right