DIY_EFI Digest V4 #460

[Greg Hermann]

>Does anyone know what the Fuel Vapour pressure for Gasoline is or where
>to look it up on the WEB?  I'm assuming (perhaps wrongly) that it's the
>pressure generated by the fuel as it evaporates.  The number used in
>Grippo's document suggests 3.1Kpa but that's at 85F.  What would it be
>at -40F.

The vapor pressure of gasoline is VERY much a matter of the blend. And most
refiners vary it from summer to winter, etc. To give you an order of
magnitude idea, the vapor pressure of iso-octoane is 1.72 psia at 100
degrees F. I do not have a listing of its critical point temp--pressure.
There is a relationship from physical chemistry that will let you calculate
the vapor pressure at any temp for about any single compound given a couple
of bits of info about it.

Regards, Greg