Fuel Econ and Hiway Mode

[Tedscj at aol.com]

In a message dated 10/12/00 8:22:29 AM Eastern Daylight Time, 
jgonyou at hotmail.com writes:

> >I don't think he was implying that inert gasses aren't compressible,
>  >just that...more gas volume (but not more petrol) + same cylinder volume  
=
>  >higher compression=better efficiency.   (of course, that's assuming all 
>  >other
>  >things being equal...which they never are!)
>  
>  Are you thinking that the EGR is in addition to the regular charge via 
>  pressure or something?  EGR replaces an equal volume of charge.  I don't 
see 
> 
>  any change in pressure.  I stand by my very-small-rocks theory.
>  
>  Jeremy

No, you're missing it...
A given volume of petrol/air PLUS an additional volume of inert gas will 
yield higher pressure (once compressed to a fixed volume) than just the 
original volume of petrol/air.  Higher pressures extract more power from the 
same mass of petrol/air, thus are more efficient.  The inert gas doesn't need 
to be non-compressable or force-fed... Simply inducted as it normally is.
The other side of the coin is that the inert gasses lower the charge temp. 
(after it's in the chamber, by absorbing heat) thus LOWERING efficiency in 
that way (lowering the temp REDUCES the pressure).  Which factor governs, I 
don't know.
Of course, maybe I'M missing something being as I only took one semester of 
physics in college, a long time ago ;)
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