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


High All, Craig here.

Here is another approach to compounding.

http://www.moller.com/files/Breakthrough.pdf

It's just a press release, but you'll get the idea.  Moller doesn't have much on the
site other than a picture of the experimental engine and some numbers about specific
fuel consumption.

They use a second rotor on the engine shaft to act as an air precompressor and exhaust
gas expander.  Same concept as turbo-compounding but with a much simpler way of coupling
the recovered energy to the output shaft.

 Obviously the second rotor won't supply as much energy as the primary (fuel burning)
rotor, but the cost of adding the second rotor without all of the fuel and ignition
accessories shouldn't be terribly high.  Also, since it should be able to  act as a
supercharger at high engine loads, it could allow the engine to be smaller for the same
maximum power output.  That might "pay for" the added cost and weight of the additional
rotor.

   Could it be added as another (identical) rotor on an Mazda 13B Wankel without too
much fuss?
  What is the phasing of the new rotor on the shaft?
 What is the volume and expansion ratio of the rotor they used?  Unknown to me.

Craig Taylor


Anything Moller says has to be taken with a grain of salt. He is in the business
of selling worthless stock and consider this an advertisement. In 30 years he has
never manufactured and sold any hardware to my knowledge.

Rolls Royce built something like this but nothing ever came from it.

Paul Lamar

Paul,

Moller's concept in theory sounds interesting but in practice he is
claiming that the pulse from an 1600 degree highly kinetic exhaust
(probably less temp. because of piping heat loss) will be timed to
coincide with the intake of a nearby rotor housing to drive it on hot
gases.  Hmm?  Vaporware:)   First this concept  puts a significant heat
loading on the cooling system, seals and rotor housings in the recovery
section.  The housing would have to isolated from the power section, be
insulated and ceramic judicially used. Still there will be heat transfer
through the e-shaft and connecting bolts. Secondly those exhaust gases
are going to have to be cooled off or converted to steam to recover
energy in the slow moving rotor.  If cooled off that means huge
efficiency losses, if converted to steam it is a good idea but it ain't
going to fly. Possible for ground based units.  For aircraft use sound
engineering has proven that a more compact and efficient axial turbine
or axial/radial combination is the best device for recovering exhaust
energy. Get it while its hot, just not too hot:)  Yes efficiency losses
happen when the speed is exchanged for torque but those numbers are
single digit now.


Doug in Japan