Math Question

[John Napoli]

This issue of thermodynamic efficiency is one of my hot points (ouch).

Fossil fuel plants use every trick in the book to recapture all the
'waste' BTUs that they can.  If you neglect the power used to run their
pollution devices (a parasitic loss), their overall efficiency is pretty
good - I recall numbers in the mid-40s.

Our gasoline engines in our cars do nothing to utilize the energy in the
waste heat.  Arre they 10%? 20% efficient overall?  I doubt 20% but lets
go with that number.

If we were able to utilize a third of the waste heat, wouldn't that make a
big difference?  Instead of raising CAFE with smaller and lighter cars, we
would raise it by being more efficient.  I doubt that all the EFI software
in the world will make much more MPG than we see right now.  I would like
to see something intelligent about using the waste heat.

John

On Mon, 16 Sep 1996, Robert J. Harris wrote:

> Remember the Reichstag
> 
> ----------
> > From: RABBITT_Andrew at mv8.orbeng.com.au
> > To: diy_efi at coulomb.eng.ohio-state.edu
> > Subject: re: Math Question
> > Date: Monday, September 16, 1996 7:06 AM
> > 
> > 
> > >The point was, is, and always will be to try to combine the sheer  
> > >power of a steam engine with the simplicity of an IC engine.
> > 
> > You can't get something for nothing.  If you have 'sheer power' then 
> > you're also burning a lot of fuel too.  Bear in mind that most 
> > stationary steam plants are working at about 35% thermal efficiency 
> > (unless they're combined cycle plants), which a good IC engine can 
> > approach too!  Therefore just adding water to fuel in an IC engine is 
> > not going to give you vast increases of power.  What it might allow is 
> > to extend the characteristic limits of an engine by a small amount. 
> > (ie the knock limit)
> > 
> > >
> Let me see if I get this thermodynamic thing right.  I burn fuel, convert 
> between 20 and 30 percent to mechanical energy, heat up cooling 
> water and oil to 200 plus degrees, and throw away 50 per cent or 
> more of the energy as heat at 1300 plus degrees exhaust temperature 
> - enuff to send water boiling at 3600 psi - and there is only a little
> teeny 
> tiny amount of excess heat to convert water to steam in the chamber - 
> as an antidetontant?  I'm convinced.
> 
> I guess I just don't get the big picture.  Maybe water knows that it is 
> about to be injected into an engine and presto magic changes 
> characteristics and doesn't boil at 212 degrees or expand 1800 times 
> when it turns to steam when that happens in a combustion chamber.
> It just stops making 600 psi at 440 degrees so that heaven forbid any
> of that wasted heat might get converted to power.
> 
> Thank you for the thermodynamic and magic lesson.
> 
>