Propane EFI

[Robert Harris]

Biggest problem with propane EFI is that it's boiling point is all over the
map - from not at -42~ to 175+ at 100f~.  This implies pumping to a high
pressure, special unobtanium injectors ( gasoline ~50 to 75~ psi) and lots of
high pressure gas in the engine compartment.  That's the bad news.

The good news is if you are a fangler, you can tell the tank company to suck
off.   Seems like a blend of liquid propane and butane about 50/50 is a direct
replacement for freon 12.   Yet did know that propane is an established and
excellent refrigerant?   Hummm  Duh - that means any small auto a/c pump and
coils can be used effectively as a pressurizing system - using a stock tank
without exotic in tank pump.  That ought to give you a bunch of dead
presidents to play with.

Next, unless I am sadly missing the point, the only advantage of liquid
propane over gaseous propane is the latent heat of vaporization.  Gaseous
propane introduced such that it can fully blend results in a homogeneous
mixture that's incredibly smooth and even burning.  This premixed gas is why
when by weight is much less than gasoline yet delivers within 10% of the
milage of gasoline.  Direct port injection will not carry much of the fuel
into the chamber liquid -44F bp and forfeit the homogeneous mixture advantage.

One alternative for fangling is to salvage a conventional water heated
vaporizer and submit it to fangle torture.   Remove the water jacketing.
Machine the upper chamber off.  Plumb the high pressure let down valve at one
end of an A/C coil and the low pressure end at the other.  Stick the A/C coil
in the intake - either the air box NA or as an aftercooler turbo'd.  Since the
only reason for the water to add enough heat to keep the vaporizer from
freezing, if the coil is large enough (not hard) it does that ok.  BUT you now
get FREE charge cooling without having to obtain unobtainium high pressure
injectors.  

Then, you can use the Ford IAC, a pulse width modulated solenoid valve to
control the flow of vapor propane with nice simplicity without forfeiting the
cooling of "liquid" injection.

For a turbo, you could go one step further yet.  You could hook up a small AC
pump at the low pressure side and as the boost pressure goes positive, clutch
it on, greatly increasing the flow of tank pressure liquid propane  thru the
coil and dump the pressurized gas back into the tank after running thru a
condenser.   

How cold would you like your fries sir?  Does an aftercooler core trying real
hard to reach -44f~ tickle any fancies, combined with the excellent
performance of homogeneous vapor?  Thought not.

On octane, reality check.  According to "Knocking Characteristics of Pure
Hydrocarbons" API Research Project 45

Critical Compression Ratios
             600rpm/212f   600rpm/350f  2000rpm/212f  2000rpm/350f  
Propane    12.2/+6g        8.8/+1g          9.0/100          6.65/96       
Toluene    15.0/+8g      11.5/+4.9g     13.5/+5.5g       9.0/+2.8g
 
Propane    R = +1.6g  M=97
Toluene    R=  +5.8g  M=+.3   Blend R = 124  Blend M = 112

No such ting as octane over 100 since 100 is pure octane.  Knock resistance is
measured as pure octane (100) + grams TEL added to pure octane to have
equivalent knock.   

Critical Compression Ratio is the C/R that knock is induced on that fuel at
that RPM and at that jacket temperature on the test engines.  Considered by
API/ASME to be a much better predictor of engine performance than R/M

Note that the effective octane of propane is significantly lower than toluene
- the most common high octane fuel component in former street gas and now
aviation and racing gas.  And its research blending octane is not 130 but only
124.   (Blending Octane is another subject ).   Note also, that as the
temperature goes up, the effective octane of propane drops radically.

1963 Ford C-600 Prison Bus Conversion "Home"
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