X-Mozilla-Keys:                                                                                 

Z wrote:

Not to say that I disagree, but I think that is

definitely an open question.  There are

two pieces to the overall efficiency equation,

first, combustion efficiency, (efficiency

of converting chemical potential energy to heat),

second, thermodynamic efficiency

(efficiency of converting heat energy to

mechanical work).

There is no question that rotary engines will

never equal reciprocating engines in

the realm of combustion efficiency, for the

reasons others have already stated.

However, it is important to remember that the

thermodynamic efficiency of the rotary

engine cycle is considerably better than that of

the piston engine cycle.  This was one

of the things which helped spur interest in the

rotary engine in the first place.  With

properly timed intake and exhaust (allowing full

extraction of the available heat energy

during the expansion phase), the greater

thermodynamic efficiency of the conventional

rotary cycle is more than capable of offsetting

the lower combustion efficiency.

If you go beyond this and start talking about

using the intake air itself to cool

the rotors and rotor housings, the achievable

overall efficiency of the rotary

configuration in fact considerably exceeds that

which can be realized in a piston

engine, a fact which the Moeller rotary has

already demonstrated.

The problem of Wankel bsfc is not combustion
efficiency otherwise the emissions would be painfully
off scale, The wankel is not a higher efficiency cycle
- since it is not a cycle but another way of
mechanically implementing the same OTTO cycle as the
piston engine so cycle thermal efficiency is tied into
the same relationship to expansion( compression) ratio
in both cases differing only in heat losses due to the
high ratio of combustion chamber surface to volume
ratio. 

The heat lost to the coolant at this point of
the cycle is most costly to efficiency. The high
exhaust temp is
a lot due to the fact of the direct port rather than
the cooling of this charge thru the exhaust valve and
port of the piston engine - (which is not lost energy
to the basic cycle -but. to the next recovery
mechanism the turbo)  The late burning attributed to
the Diesel
cycle is a loss of thermal efficiency, which in real
operation is compensated by the increased expansion
ratio from the high compression ratio associated with
the Diesel operation.

A somewhat related thought - M. Zoeche complaining
about the spark ignited "Diesel" Wankel is that
compression ignition is not a part of the theoretical
cycle at all - Also - does spark ignition of the heavy
fuel with Diesel type direct injection timing negate
the meed for "octane"? Vance



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