Heat recovery systems

[akkudakku]

Hey guys, I'm back with a question again.

Have anyone of you ever tried to build a heat recovery system for your engines?
From what I understand of the theory of the turbojet/turbo-shaft engines - power is a function of TIT, TIT is increased by burning fuel and PR determines burn efficiency.

So now what happens on a turbo-shaft if we take the hot exhaust and heat up the air coming out of the compressor just before the combustor with some kind of heat exchanger? From what I understand this way we should use less fuel mass/kW.

Another idea that springs to mind is using the hot exhaust to heat up fuel before it reaches the combustion chamber - it would work great with liquid propane or LPG supplying the heat of evaporation and evaporating it 'for free'.

Could systems like this be used to get better specific fuel consumption?

[racket]

Yep, better SFC if you can use some of the "waste" heat .

I haven't heard of any DIY application , probably because we aren't too concerned with fuel burn rates because of the limited run times , its not worth going to all the trouble and expense, we'd spend more on the heat exchanger than we'd ever spend on fuel .

Cheers
John

[akkudakku]

What about sequential combustion in free-power gas turbines John?

I know it is actually increasing the fuel consumption, but what would be the result, increased shaft power?

By the way could you recommend a lecture about gas turbines to me (I'm wondering on the thrust -> power estimation and the thermodynamics of power generation on the free-power)?

[racket]

A second combustor can be used to "reheat" the gases before entering the freepower turbine for a bit more power, but it does add a lot more complication and size to the build.

As a rough guide, for every pound of thrust we can make from a DIY engine we should be able to produce a horsepower , 100 lbs of thrust = 100 horsepower.

Do you have the Thomas Kamp book , if not , purchase it direct from the publishers, gb.trapletshop.com/model-jet-engines-3rd-edition-by-thomas-kamps ...........its the best book for beginners , the thermodynamics for the gas producer can be applied to the freepower

Cheers
John