Accel enrichment

[Raymond C Drouillard]

On Mon, 23 Mar 1998 11:26:05 +0000 "Zack" <zubenubi at inetport.com> writes:
>Joe,
>
>Mmm, but if you are compressing the gas the temperature is also going 
>up (if you are compressing fast enough that things are roughly 
>adiabatic), which raises the vapor pressure.  In most regimes vapor 
>pressure of a liquid or solid rises so quickly as a function of 
>temperature that this is the dominant effect if the change is 
>adiabatic, so that increasing pressure increases "solubility" of 
>liquid droplets, and decreasing lowers it, hence the observation 
>about rising columns of air and falling barometric pressures 
>signaling cloud formation and rain, which someone brought up earlier.
>	If the change is isothermal, then in that regime, it would be 
>correct to say that raising the overall pressure would cause the 
>vapor to start condensing out, and vice versa.
>	The question is, at which end of the scale are we??  This is 
>where 
>my theorizing ends and we need an experimentalist to step in.
>
>Zack
>
>So full of hot air I need to keep my hat tied on a string...:-)
>
>> 
>> Oh yea, that partial pressure thing.  I remember that.
>> 

It isn't adiabatic or isothermal compression.  It is nowhere near being a
closed system.  We don't have a fixed amount (number of moles) of gas
being compressed.  We have a small space that is partially evacuated that
is suddenly inundated by gas that is already compressed and is already at
the ambient temperature (whatever that happens to be).  The fact that
it's rushing in to fill a partial vacuum isn't going to raise its
temperature.  There might be some insifnificent amount of heat added
because of friction, but I still doubt that's significent.

The truth is, I suspect that it's hotter than ambient temperature inside
the manifold, and the inrush of air has a cooling effect.  Remember, a
"wet" manifold is purposely heated by the exhaust.  Most other manifolds
are close enough to the rest of the engine for some heat to be
transferred, especially in a vehicle with EGR.  At partial throttle,
there is less gas flow to absorb heat than at full throttle.

Ray Drouillard
(still trying to earn that hat)

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