On Mon, 05 Jan 2004 23:26:51 +0000, "Andrew Heggie"
wrote:

On Sun, 04 Jan 2004 23:10:56 GMT, (QrizB) wrote:

Not true. Think about the phase diagram. At temperatures above the
triple point of LPG, the vapour can have the same density as the
liquid.

Triple point is -190C

That's also the melting point - liquid and solid present in
equilibrium any vapour will need to be at very low presure. At -42C
(boiling point) vapour pressure is taken as 0 psi gauge (14.7 psi
abs).

A quick calc suggests that the gas will compress to the same density
as the liquid at about 300bar (needs checking). Keep your pressure
above this and you would see no difference. Of course in practice if
you keep the pipe runs away from the head the heat exchange surface at
the injector will simply not transfer enough heat to cause a problem.
On stopping the gas would just occupy a small section of the injector
pipe which was above 97C.

AJH

I think he meant above the critical temperature when it is no longer a
gas or liquid but a supercritical fluid. The usual condition of
propane in automotive use is somewhere between it's boiling point and
the critical temp. As a supercritical fluid the density changes with
temperature just like vapour. Changes in fuel density with temprature
on normal EFi systems are taken in to account by the manifold temp
sensor or hot wire AFM, it's assumed the fuel temperature tracks
ambient. Using propane in the supercritical region would require
sensors for fuel pressure and temperature with an ECU stored map to
give the density of the fuel. Not impossible but a real pain to have
to implement yet another map with two variables for look up.

--
Peter Hill
Spamtrap reply domain as per NNTP-Posting-Host in header
Can of worms - what every fisherman wants.
Can of worms - what every PC owner gets!