[Diy_efi] LPG injection

[Greg Hermann]

At 9:58 PM 11/17/02, sy2th wrote:

Several urban legends to de-bunk here--

First-- "SUBLIME" means a phase change from SOLID directly to GASEOUS
state. NOTHING to do with liquid state !! As when snow evaporates directly
into the air or dry ice (frozen CO2) changes directly to a gasseous state
without becoming a liquid first.

Second-- While it's entirely possible that injecting liquid propane could
cause THROTTLE icing under properly conducive atmospheric conditions (high
humidity), the injectors would NOT be at all likely to ice.
The source of the water ought to be obvious from the "high humidity" part
of the above !

Third-- Conventional propane carburetor systems absolutely do NOT draw gas
off of the top of the tank !! They use a dip tube and draw LIQUID off of
the bottom of the tank. The liquid then goes through the "vaporizer"--which
uses warm engine coolant to vaporize the liquid before it goes to the
carburetor. The tank would turn into an ice ball (again, from atmospheric
humidity) if one even TRIED to draw the quantity of gas off of it that even
a small engine uses under load !! ) (Not to mention that you simply would
NOT get ENOUGH gas out of the tank to let the engine run !!

Greg

>Well, maybe I need correcting also, but that makes absolutely NO sense to
>me.  "Freeze" meaning ices up?  Where does the water come from?  It would
>have to be in the gas for that to happen, and lots of it.  Nitrous comes
>out of the nozzle every bit as cold as propane, never heard of any
>'freezing' problems.  The LPG systems I've seen draw vapor from the top of
>the cylinder, not liquid from the bottom as nitrous systems do, so what
>gets cold is mainly the tank & the delivery line.  Remove the nozzle from a
>propane torch & open it, aimed @ your hand - not real cold at all, but the
>tank chills.  Now, invert the tank, so's liquid comes out - - bit of a
>different situation, no?  Somehow, I don't think so, Al.....
>
>Barry - Sy#26  -  (but, hey, I'm no expert.....)
>Bangor, MI
>
>At 10:19 AM 11/18/02 +1100, you wrote:
>>Glynne,
>>         I stand to be corrected, but from what I understand there is one
>> major hurdle which has dogged the concept of LPG injection. And that is
>> the "Latent Heat of Vaporisation" of the LPG. The reason is that liquid
>> fuels are injected as microfine droplets, but still a liquid however when
>> you try to inject LPG it submilates, IE it turns directly from a liquid
>> to a gas. To do this it absorbs heat from the surounding structure(metal,
>> air, etc) - large amounts of heat - much more localised cooling than the
>> waste heat into the area from the combustion chambers - and tends to
>> freeze the injector - literally freeze it solid (either open or closed!)
>> - thus end of control, BIG problems! This problem may have been solved,
>> but to my knowledge has not yet been. This is obviously a much more
>> fundamental issue to resolve before considering an ECU!
>>Regards
>>Bill W



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