Alternate fuel EFI

robert dingli r.dingli at ee.mu.OZ.AU
Wed Mar 20 01:08:35 GMT 1996


Michael Fawke and Stephen Lamb have both described the same LPG injection
system.  The system was developed by Liquiphase Injection (formerely known
as Biocom) in South Australia and has received support from Ford Australia.
The LPG efi system was developed by Injec Racing Developments who previously
marketted an aftermarket efi product of dubious quality.

Just to expand on some of the technical details..

The injectors are modified standard Bosch injectors as used on the Ford
Falcon (6 cyl 4.0 litre).  To overcome LPG vapourisation problems within the
injectors (which tend to freeze them), they decided to create a bottom feed
injector to minimize the flow path for the delivered fuel.  This modification
involves machining a slot into the base of the Bosch injector and fitting a 
separate LPG feed fuel rail.  The unsed LPG is fed back to the tank via the
standard petrol fuel rail and some solenoid valves.  The LPG is fed to the
engine by an in-tank efi pump.  While the pump creates a pressure differential
required to flow the LPG, the absolute pressure of the fuel is governed by
the temperature of the tank (butane/propane vapour pressure) which varies
greatly. The vapour pressure is far in excess of the pump pressure and hence
a fuel pressure regulator wouldn't be able to maintain a constant pressure
differential.

While it is an interesting approach there are a few technical problems.

The injectors, now running at much higher pressures, require a much higher
operating voltage to pull them open.  There is also the issue of machining
debris falling into the injectors during the slot cutting operation and the
errosion that would be expected within the injector due to LPG vapourisation.
It would be interesting to see the injector durability stats.

The recirculating injection system adds a lot of heat to the fuel which is 
returned to the tank.  During initial runs they resorted to surrounding the
tank with ice but I don't know of a long term solution.

The last problem is the petrol/LPG switchover which I know is slow and
cumbersome.  I have heard stories of LPG bubbling through the petrol tank.

Since LPG is such a good fuel (very cheap and easily obtainable in Australia)
I can't see why they opted to make the system dual fuel in the first place.
A single LPG fuel system would make more sense and solve many of the problems.

Just my thoughts.

Robert
-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **



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