[Diy_efi] LPG injection

[Greg Hermann]

At 11:48 PM 11/21/02, Derek wrote:
>"Simply evaporates." You are aware the latent heat of vaporization of methanol
>is 3340 BTU/gal? That's a LOT of heat getting taken out of the air. Guess what
>propane's is.....only 775. You also will use much less gal/min of propane,
>as it
>does have 243% as much horsepower per gallon. Not a problem with methanol, just
>spray more. So let's say you are injecting 200HP worth of fuel (propane or
>methanol) on top of your gasoline.
>
>You will get (3340/775)*2.43=10.47 times as much charge air cooling with
>methanol
>
>Do the math before making assumptions.

I HAVE done the math, apparently in a great deal more detail than you have.
But--one needs to have an understanding of the physics, physical chemistry,
and thermodynamics as WELL as the math before simply applying the math.

The FACT is that you are not going to get nearly as much "charge air
cooling" as you call it out of methanal as you claim from the simple
numbers--because the intake air stream will be cooled sufficiently to reach
the saturated partial vapor pressure of methanal LONG before all of the
methanol has evaporated. The REST of the methanol will enter the cylinders
in (hopefully atomized) liquid form, and the latent heat of vaporization of
this remaining liquid methanol will act as an internal coolant during the
compression stroke--reducing peak compression pressure, negative work to
perform the compression, AND the peak compression temperature. In fact--a
stoich mixture of methanol has SO much latent heat of vaporization that
there will STILL be some liquid methanol left at the top of the compression
stroke, even with a compression ratio in the 12 or 13 to 1 range !! The
last of the liquid methanol is actually evaporated by the initial heat from
the flame front when running pure methanol fuel at stoich or richer !!

On the other hand, propane has a MUCH higher saturated vapor pressure, IAT
for IAT than methanol does, so you are quite likely to get MORE net charge
cooling from liquid propane than from methanol, regardless of the fact that
its latent heat of vaporization is less.

AND--talking about latent heat per "GALLON" of any fuel is a joke. At least
talk in terms of latent heat per pound. Better still, talk about latent
heat of the fuel for the weight of fuel needed to make a stoich mixture
with one pound molecular weight (one mole) of intake air. Doing so would
put things on an apples to apples footing.

Greg


>
>Direct LPG into the ports is nice, good high octane fueling suppliment. But if
>you are going for charge air cooling, propane isn't your choice.
>
>I DO get those temps. I can make up a graph from one of my logs if you like.
>
>> <cough> I really doubt it, LPG goes from compressed liquid
>> to a gas - mthanol simply evaporates, the discussion is about
>> direct LPG injection into the ports...
>>
>> rgds
>>
>> mike
>>
>> At 03:35 PM 18/11/2002 -0800, you wrote:
>> >LPG gas cools very little. Methanol will be 10x better for charge air
>> cooling. I
>> >should know, I get intake temps lower than 20F on a 70F at 30psi of boost.
>
>
>
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