[Diy_efi] Re: Diy_efi digest, Vol 1 #363 - 9 msgs

[Bill Washington]

Gents,
    I have not tried it, but am only relating what was said by some fuel 
injection professionals during a presentation at our car club.
I suspect that since injectors are designed to work at ambient temp and 
upwards, the variety of materials used in the injectors are such that 
the differential rates of thermal expansion/contraction are designed for 
that temperature range, not for the -20 to -40Deg Celcius that would be 
experienced in injecting LPG, when there may be mechanical seizure due 
to differential contraction.
    1. Remember that these are precision devices, therefore the 
tolerances are very close, so only a very small differential contraction 
in the wrong direction would be necessary to seize up the injector.
    2. In injecting LPG it MUST be injected as a liquid to achieve any 
consistency in metering with existing injectors which are all designed 
to meter liquids.
To inject it as a gas I suspect that the injector would have to be a 
radically different design.With a liquid a slight change in feed 
pressure will affect only the flow rate, whereas with a gas a slight 
change in pressure affects density and flow rate, the pressure becomes 
much more critical in trying to achieve a known metered volume of fuel!

Message: 7
Date: Sun, 17 Nov 2002 21:58:52 -0500
To: diy_efi at diy-efi.org
From: sy2th <sy2th at direcway.com>
Subject: Re: [Diy_efi] LPG injection
Reply-To: diy_efi at diy-efi.org

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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