EFI for Propane

[Greg Hermann]

>> The pump would pressurize the propane to arount 330 PSI.  This would be
>> fed into the input side of the injecter.  The output side would be
>> connected to something similar to a diesel injecter, which is a valve
>> that opens at a specific pressure.  If it is set to 300 PSI, the injecter
>> will "see" a pressure differential of 30 PSI, and will be fed with
>> relatively warm propane.
>
>You don't need a pump if you take propane off the bottom of the tank -
>called liquid withdrawal. This is standard for automotive propane
>systems. It IS liquid when it hits the "evaporator" - you know, that
>water heated thingamagig used on "carbed" propane units. The pressure
>varies with tank(vapour) temperature - not with fuel level, so it would
>not be hard to calibrate an EFI to use liquid propane. The problem I see
>is getting an injector to do the deed. Mabee try the electronic
>controlled injectors from something like a Ford Powerstroke or
>electronically managed Cummins or Mack. Not sure how they work, or if
>they require lubrication. Size the injector to flow 15% more fuel than
>you would use for gasoline to start because energy density of propane is
>about that much lower (If I remember correctly - my propane days go back
>a little while)
>The big problem, at least here in Ontario, would be getting the bugger
>certified so you would be allowed to re-fuel it. Lots of little things
>you would not think of, I'm sure.

----------------------------------------

Lower heat of combustion for propane is 19,768 BTU/lb.

Lower heat of combustion for iso-octane is 19,065 BTU/lb.

Reason propane fueled engines are down on power is largely due to greater
displacement of intake air by vaporized fuel than what happens with
gasoline, due to lower molecular weight of propane compared to gasoline. No
latent heat effects in inlet tract or during compression stroke with
(pre-vaporized) propane are the other effects. Also slightly less heat of
combustion at stoich for a given mass flow of air with propane, but
certainly not 15%.

Stoich A/F ratio for propane is 15.7:1 (by weight).

Flow through an injector will vary with the square root of the pressure
difference across the injector.

MASS Flow through an injector will ALSO vary with the square root of the
density of the liquid going through it. IF NO FLASHING OCCURS!

 If you get any flashing (into vapor) in the injector, all quantitative
bets on flow rate are off (except that it will be lower than with no
flashing), but MORE IMPORTANTLY, the flashing WILL erode injector parts
pretty quickly if they are not made of the right stuff! For decent
durability with flashing going on, you would likely need 400 series
Stainless at a minimum, or maybe carbide or stellite for parts in contact
with the flashing.

Regards, Greg