[Diy_efi] Liquid Phase Propane Injectors

[Mazda Ebrahimi]

Greg, can you explain further? Here's an example.

You fuel up the first time... assume 95% propane, 5% butane.
I don't know which would have a higher vapor pressure... let's assume
butane.
So, let's say the liquid is 96% propane, 4% butane, and vapor is 94% and
6% respectively.
Since we use liquid (and I agree even the carb systems use the liquid
draw), we continue to use 96% propane and 4% butane.

Next time we refuel, we add 95% propane, 5% butane.  But butane
concentration of existing fuel in the tank is higher.  Therefore, when
equilibrium is achieved, the overall butane concentration is increased.

I agree this is fairly minor in terms of overall fuel composition; well
within the ability of adaptive learning.  Even open loop carbs don't
have a problem with multiple refuels.

I experienced a problem with this when I converted a truck to LNG.  The
composition of fuel sample in our tank didn't match the fueling reports
we had from the supply.

Thanks
Mazda

-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
Behalf Of Greg Hermann
Sent: Friday, May 31, 2002 10:28 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] Liquid Phase Propane Injectors

At 11:02 AM 5/31/02, Mazda Ebrahimi wrote:
>Hey all,
>Just wanted to chime in on the fuel quality issue.
>
>Another problem with varrying fuel quality is related to thermo
>properties of the various compounds sold as 'propane'.
>
>It's been a long time since I cracked a thermo book, but from what I
>recall, based on their individual PV diagrams, each component (propane,
>butane, etc...) will achieve equilibrium at a certain volume given
>pressure and temprature.  That means that certain compounds will occupy
>the vapor space in higher relative concentrations than the liquid
space.
>
>As you keep refilling each time, you will use less of the compounds
that
>have higher vapor concentration.  So over time, the composition of the
>fuel in the tank is actually different than what you're putting in
>(unless you use up almost all the fuel regularly).  This could be
>another explanation for varrying fuel composition.
>
>I don't pretend to be up on my thermodynamics.  Perhaps someone more
>qualified could verify or discount the logic here...
>
>-Mazda

Accurate statements, but not really applicable to propane (gas OR liquid
phase) fueled engines.  Even the gas phase carbys feed the LIQUID fuel
from
a dip tube at the bottom of the tank to a "vaporizer" which is heated by
engine coolant. So, because the liquid is constantly "blown down", the
concentration of higher boiling components does not occur.

Greg



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