Dear Sir / Paul Lamar,

I am fascinated by your articles on turbo compounding.

Having no technical backrgound however makes it hard for me to grasp some of
the basic enegy converting processes that take place.
I hope you are willing to explain this to me (preferrably is in simple
language).

If I am correct there are three energy components in exhaust gasses that
potentially can be changed into kinetic energy (ie of a shaft)
a) high temperature of exhause gasses vs low outside temperature

b) high pressure and speed of the exhaust gasses vs normal pressure of the
surrounding air

c) unburnt fuel in the exhaust gasses

b) is obviously used by making turbine blades rotate. I can see that

But you also state that kinetic energy is the result from lowering the
temperature of the exhaust gasses.
I understand that a temeperature drop means that the energy has gone
somewhere else, But how does this process of converting thermal energy into
kinetic energy take place in the turbine?

Also you state there is potential energy to be recovered by burning the
remainder fuel in exhaust gasses.

Burning gasses in a turbine is a commonly used technology.
One wonders what would be the benefit of starting off with an internal
combustion engine and ending with a turbine engine.
The combination always seem to lead to a heavier and thus unvavorable
solution.

Erik Kappelle

"you also state that kinetic energy is the result from lowering the
temperature of the exhaust gasses."

I don't recall saying that. The opposite is true. I wrote several articles
and gave several video presentations. In which article did that appear?
It may be a typo.

"Also you state there is potential energy to be recovered by burning the
remainder fuel in exhaust gasses."

Merely running the engine lean, up to a point, will increase the exhaust gas
temperature as unburned fuel will be burned that will increase both kinetic
and thermal energy in the exhaust. If that does not do the trick pumping fresh
air into the exhaust ahead of the turbine will take care of the residual.
That was widely used in early rotary engine to reduced unburned hydro carbons.

This increases the kinetic energy available for recovery.

Weight is not everything. If that were the case nobody would use anything
other than a turbine. BSFC is important. BSFC is short for Brake Specific
Fuel Consumption which is a number that specifies the pounds of fuel burned
per HP generated for one hour.

Small turbo prop engines have a typical BSFC  of .65. The turbo compound
rotary will be nearly half of that or around .35. Cost is also important.
A turbo compound rotary would also be close to half the cost of a small turbo
prop engine.


Paul Lamar