Propane Motor Fuel Injection

[robert dingli]

Hi everyone,

Bonn Macy and others have questioned the use of propane and CNG,
> 
> Speaking of CNG and propane systems, could anyone give me a quick rundown on
> what is involved with a CNG injection (or carburetor) system in a car
> compared with a gasoline system?  I would also be interested in any energy
> efficency and economic issues invovled with CNG relative to gasoline.
> 
> Would a CNG system designed from a clean sheet of paper be different than a
> CNG conversion system?  What advantages would there be?
> 
> Thanks,
> 
> -Bonn Macy
> 

CNG has several major advantages over petrol and some major disadvantages.
Its main disadvantages are mainly due to being stored as a gas, leading to
large, heavy, high pressure tanks and limited range.  Distribution (at 
least at high pressures) is also an issue and from what some of our research
has uncovered, gas composition can be a problem.

CNG is anywhere from 80 - 95% methane which has an octane rating of 130.
To combat the limited range, much work has been done to increase the 
efficiency of the available fuel usage.  Research in our labs at Uni has 
focussed on high turbulence (for better mixing) and high compression 
designs.  The compression ratio of the base engine has been raised from
9:1 to nearly 16:1 and has been extensively tested in a taxi fleet.  The
peak thermodynamic engine efficiency has been raised from around 32% to
over 40%.  In one of our applications which operated at a more
representative partial load condition, we attained near 50% increase in
efficiency over the standard engine.  The current system uses special
injectors in place of the standard units, the original fuel rail and
the original OEM computer recalibrated.

Locally available LPG (used in a significant portion of the Australian
car and truck fleet including all taxis) is roughly a 50/50 mix of propane
and butane and has an octane rating just under 100.

LPG injection is being trial by a South Australian company called Biocom.
Their system uses modified Bosch injectors to allow the LPG to be fed to
the base of the injector, while the petrol travels through its normal
path.  They use an efi pump immersed in the tank so that they can
recirculate the LPG.  There are many problems with the design, but
they appear to have sufficient funding to continue research and trials.

Robert Dingli
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 9344 7966                          (+613) 9344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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