[Diy_efi] LPG injection

[Greg Hermann]

At 10:40 PM 11/22/02, Grant Beaty wrote:
>> 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 !!
>>
>> Greg
>
>Is this a bad thing?

In some ways. It's for SURE why methanol fueled engines tend to foul the
plugs before they are warmed up!!  It also is REALLY bad for the efficiency
and hurts the power output when some of the heat of combustion goes into
evaporating the rest of the fuel !

You're getting right AT the reason why some of the mfgr's have played with
that 80/20 ethanol/gasoline mix. At stoich, the latent heat of vaporization
of that mix is just about PERFECT for having the last of the fuel get
evaporated JUST as the spark plug ignites it.

It seems like methanol would be very good at
>surpressing det if this were the case.

This very much IS the case, and methanol IS excellent at avoiding detonation.


 I realize that cooling after the
>intake valve has closed does not help the engine ingest more air,

Right, but it sure as h*ll DOES reduce the amount of negative work needed
during the compression stroke.

The lower peak temps (all the rest of the way through the cycle) are GREAT
for durability, and also put a BIG dent in the amount of heat rejected to
the water jackets. The latter good for both power and efficiency.

On the other hand, the lower peak temp after combustion means less
mechanical work out of the gas during the power stroke (for a given
compression ratio). Net improvement--less positive work vs. savings in
negative work tends to run about 1.5%.

The slower flame speed with methanol vs. gasoline hurts the cycle
efficiency a bit, and also cancels some of the detonation resistance.

but one
>can always turn up the boost.
>
>Lots of charge-air cooling without increasing the pressure ratio could push
>a turbo out of its effeciency range, although it would of course depend on
>the turbo.

Sizing is EVERYTHING with a turbo. You GOTTA know where you're trying to go
before you pick one. :-)

Not to mention that injecting SOME of the methanol pre-turbo (under boost
conditions only) would put some internal coolant into the
compressor--reducing the work needed to do the compression, thus ultimately
reducing backpressure on the motor from the turbine, and possibly
eliminating the need for an IC.

Greg
>
>The end goal here is (of course) the most amount of power.

Depending on what you're doing, getting lower bsfc is at least as worthy a
goal, and it's a GREAT one if you can get MORE power while doing it !! :-)

Greg

If you must turn
>up the boost to achieve more airflow, I don't see how thats any better or
>worse than increasing air density.
>
>Grant
>
>>
>>
>> >
>> >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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