Propane EFI - part duece

[Franc Buxton]

Gerald Pelnar wrote:
> 
	(quoting me):

> > according to the gas laws, the pressure will be:
> >
> >       10000/44 = 227 bar (!). (Plus a bit for temp. difference
> from
> > Standard Temp.)
> 
> The problem with the calulation is the condensation of the
> gas.
> Once the gas becomes saturated and condenses, it no longer
> maintains ideal gas properties, It changes to follow
> properties
> of saturation. You mention maintaining propane at 50 deg C.
> At this temp vapor pressure is about 230 psig. (16.6 Bar?).
> 

> >       Am I barking up the wrong tree, or is this just slightly
> scary?
> 
> Yep and Yep.
> I personally find the prospect of heating propane very
> distasteful.  :)
> Which brings me to my question. I have read and re-read
> this thread.
> I'm a little confused. I thought the idea was liquid
> propane injection.
> If this is true, why the concern with critical temperature.
> Critical
> temperature is the point at which any increase in pressure
> of a
> gas will not cause condensation. Hmmm... no condensation,
> no
> liquid to inject. I know what ever I missed has got to be
> simple,
> but you're going to have to help me out.
> 
	I understand saturation equilibrium (at least that much)
but my concern was with critical temperature, above which there
can be no condensation (by definition), therefore no equilibrium.
- In which case my question should maybe be: At what point does a 
gas begin to obey the ideal gas laws? I understood that point to be
the critical temperature, but I'm quite happy to be corrected by
some of you guys, who obviously have far greater practical
experience than me. This is probably not quite the appropriate
forum to discuss this too much further, but it has raised some
intriguing questions for me!

	Just to clarify, Gerald, my concern with critical
temperature was simply because it is so _close_ to the temperatures
at which the liquid would have to be controlled, and the problem
would be to _prevent_ the liquid reaching that inadvertently. The 
root of my concern is my discussion with a firefighter friend who
expressed absolute horror at the thought of heating a propane tank
for any reason at all. I understand that if there is any risk of a
tank in a fire even approaching that temperature, the fire services
will consider evacuating the area and leaving the fire to burn!
Considering that engine coolant can reach 110 deg C, there is a
finite risk of overheating if it is used, although admittedly less
if indirect.

(Just to recap, the need was to attain a controllable temperature
- and hence pressure (only true for a liquid/gas equilibrium) - 
which therefore would need to be above ambient _anywhere_ in the world).

	Also, Greg, I understand about test pressures and working
pressures (I am a scuba diver), sorry to be vague, but I didn't
(and don't) know the actual figures for propane storage tanks. I
do know that the certified pressure (about half the test pressure? - 
two-thirds in the case of scuba air cylinders) should not be exceeded
in normal use, and that on a propane tank an over-pressure valve or
blowout plug will activate around that point. I suspect that a special
tank would need to be designed to work with propane at above 50 deg C,
since standard ones may be near their operational limits, especially
considering the steep rise in vapour pressure with temperature at that
point. Can anyone confirm?

	Thanks for the intellectual stimulation, gents, I'll now
go learn some more...

	Regards,
		Franc.

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