> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Brooke Clarke
> Sent: 18 August 2010 17:53
> To: piclist@mit.edu
> Cc: Russell McMahon
> Subject: Sterling Engine Metrics
>=20
> Hi Russell:
>=20
> In your post today you mentioned "There are many descriptions for low
> power units, most not aimed at a quality product or high efficiency."
>=20
> Some years ago I attended a talk by Pete Brock (designer of the Cobra
> Daytona coupe) where he talked about the engine he was developing.
> It was designed to operate at a low Brake Mean Effective Pressure
(BMEP)
> which is very different from most automotive engines. The problem
> started when automobiles first came out and were taxed on formula
> horsepower.  For example the Rolls Royce Phantom was called the 40/50
> meaning you paid tax on 40 HP but the engine delivered 50 HP.  Most
car
> racing classes encourage getting the most HP per cubic inch of
> displacement, i.e. high BMEP engines.
> http://www.prc68.com/I/Cars.shtml#LowBMEP
> http://en.wikipedia.org/wiki/BMEP
>=20
> But if you look at other forms of transportation there are other
metrics
> for their engines.  For example for aircraft it's reliability and
> HP/pound.  For ships it's HP/(pounds of fuel burned in an hour).  In
> both these cases the engine is a low BMEP design.  This is closely
> related to specific fuel consumption:
> http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

This isn't quite true, BMEP gives you a sort of "specific torque" value,
i.e. a measure of an engines capacity to do work which is independent of
displacement.  A low BMEP does not necessarily translate to a low
specific fuel consumption - low BMEP could be caused by low thermal
efficiency (e.g. low compression ratio) which would degrade specific
fuel consumption rather than improve it.

Also check out the big Sulzer two stroke diesel engines used in many
ships, they have exceptionally high BMEP (as high or higher than a
turbocharged four stroke diesel).

Regards

Mike

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