Propane Motor Fuel Injection

[dn]

> I heard of an HEV (Hybrid Electric Vehicle) team using compressed natural
> gas (CNG) and I asked them specifically about the metering and pressure
> regulating problem.  If I remember correctly they had a regulator at the

CNG is somewhat a different can of worms in that the fuel is in gaseous
form in the tank, under super high pressure (4000 psi).  The regulator 
used for this would be just a standard 2 stage gas regulator similar to
what you would find on an oxy-acetylene torch system.  Propane, on the 
other hand, is liquid in the tank and is vaporized prior to delivery to
the carburetor.  Much more difficult to regulate the pressure on this type
of system, since when you reduce the pressure, the liquid propane tends to 
boil, and you then have a real mess on your hands.  The advantage to keeping
the fuel liquid until the last possible moment is that the plumbing has to
be much smaller from the tank to the carb.  If you tried to take gas directly
off the tank you would have to have 2" diameter fuel lines in order to get
enough fuel flow!

> output of the CNG main tank (actually a pressure transducer and a solenoid
> valve, but that may not be necessary) leading into a plenum or reserve
> tank.  It simply opened and closed the valve to keep the desired pressure
> 

Now you're cookin', this may be the way to go.  PWM a valve, and use a pressure
sensor to keep downstream pressure at an average based on flow demand...
May still have problems with keeping the fuel a liquid, though.  Anyway,
Thanks for the info.

Regards, Darrell



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