LPG/CNG octane rating

[Doug Rorem]

>     A while ago, there was some discussion about the octane rating of 
>     LPG/CNG around the world, and as usual when you need that bit of mail 
>     you can't find it.
>     
>     Can some one refresh my memory of what it is in US, Canada, Australia, 
>     New Zealand, any other places.

Dan,
Here's two previous messages that dealt with CNG and octane..

Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca (wrote):

Compressed Natural Gas (CNG) does have an octane rating somewhere near to
130 - you can run 25 degrees initial advance, and upwards of 35 total.
It's cheap, (at least here in Canada), and it has VERY low emissions.
Having said that, it is stored in tanks at up to 3000 PSI, which means
they are big, heavy, and they don't hold much fuel.  Typically, range is 
very limited.  It's hard to find fuelling stations, (getting a bit easier)
and it takes half an hour to fill up.  Plumbing and installation is very 
expensive, all stainless hard tubing (no hoses allowed).  Doesn't have as
high a specific energy rating (per lb) as gasoline, making fuel consumption
much higher.   All in all rather impractical for a street vehicle.  There's
no reason you can't run turbos and high compression with CNG, it's just
that nobody does... (Taxis, couriers, etc use it somewhat, and our local gas 
company's service vehicles are all CNG - it figures)  

Propane (LPG), however, has a pretty good octane rating(110-115), is also 
cheap, clean, and the tanks and plumbing are much lighter and less costly 
since you only have to deal with a couple of hundred PSI.  Tanks also hold 
more fuel since it is in a liquid state instead of a gas, and you can get 
it anywhere.  Ideal fuel for use with turbos and superchargers.  All in all 
IT IS a good fuel for a street/high performance vehicle.

Both fuels promote long engine life because of the cleaner combustion and
the fact that these fuels are not solvents like gasoline and don't wash the 
lubricating oils off cylinder walls and valve guides, etc, thus prolonging
their life substantially.  Half a million miles is not too unusual between
rebuilds on a propane engine, if it was built specifically for propane in 
the first place...


Robert Dingli   r.dingli at ee.mu.oz.au (replied):
While on the topic of CNG/LPG...

There is a fleet of port injected CNG taxis running around in Brisbane, 
Australia as well as some in New Zealand.  For our single fuel application, 
the compression ratio was raised from about 9:1 to well over 15:1, and the 
resulting peak efficiency increased from about 30% to over 40%.  Natural gas 
in Melbourne is relatively consistent (but not available in CNG form) with 
a RON of 140-142.  In Brisbane and NZ the methane ratio can be as low as 90% 
lowering the RON to about 130.

To test various methane / propane ratios, we recently installed a second set
of gas injectors with an adjustable pulsewidth proportional to the base 
injector pulse from the Ford EECV ECU.  Could this be the ultimate dual fuel
combination?

The project was set back a little last week when the dyno drive shaft flex
coupling decided to let go and hurl itself through the bell housing and
steel safety cover, across the lab, through a window and into the car park
onto an unoccupied Nissan.  Luckily no one was hurt, but the mechanical
casaulties include the drive shaft, engine crankshaft, dyno shaft,
bell housing (now lots of little pieces of aluminium) and safety cover.

LPG in Australia can have as much as 50% butane which lowers the octane rating
to just under 100.  Unfortunately this is little better than the leaded fuel
that about half the cars on our roads still use.

--
Doug Rorem
University of Illinois at Chicago         (312)-996-5439  [voice]
EECS Department  RM 1120                  (312)-413-1065  [fax]
851 S. Morgan Street                      (708)-996-2226  [pager]
Chicago, IL 60607-7053                    rorem at uic.edu