Alec Cameron said the following to Craig Healy on the subject of
Chevy Co-Gen investigation (09 Nov 97  17:47:56)
 AC> Hi Craig
 AC> On (24 Oct 97) Craig Healy wrote to All...
 CH> a modified Lister engine.  He claims better overall efficiency
 CH> for the gas unit - around 93%.  Diesel is about 90%.
 AC> ^^                    ^^
 AC> I hasten to say, I am not an engine expert. But am certain, that those
 AC> efficiency figures are grossly overstated. For an engine there is only
 AC> one accepted formula for efficiency and that is
 AC> (100 times [Energy Output divided by Energy Input])  percent.
 AC> For practical engines the usual value is way below 50%, most of the
 AC> fuel being wasted out the exhaust and thru the radiator.
 AC> The guy who claims 93% is maybe a salesman, with a weird definition of
 AC> Efficiency. Like the weight loss clinic who reduce a woman's size by
 AC> 18 inches: 1 inch off the neck, 3 inches off each thigh, 6 inches off
 AC> the waist and 8 inches off the hips- an overall reduction of 18 inches!
 AC> Oh yes, and the wallet gets greatly reduced too! ;-)
 AC> Cheers.........ALEC
You're right. The theoretical maximum efficiency of gasoline is just
under 30% (heat into mechanical). A lot of the energy balance in the
chemistry of combustion goes into the byproducts exiting the tailpipe.
Maybe he was comparing how close he gets to the theoretical maximum with
this 93% figure?
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