Damon wrote:
What combinations of fuel and engine produce the least amount of pollutants?
In this question, i am including the impacts of actually
producing/transporting/etc. the fuel, as well.  (i remember someone
mentioning this a while back, but can't find it in the archives).  How does
natural gas, or possibly even fuel cells weigh in to the global-efficiency
calc compared to your standard gas and diesel?
It sounds like a simple TDi is a viable option for these criteria, but i
want to see even *more* numbers! :-)

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Where I live, western Canada, there are several alternative fuels currently
available.  They are: propane, methanol (not sure what percentage) and
natural gas.  Propane is by far the most common, the distribution
infrastructure is well established so availability is not a problem.
Natural gas, however, is the cleanest followed by propane.  My vanagon is
dual fuel, burns either propane or gasoline.  I've had the van on a gas
analyzer and propane is much cleaner than digifant.  I suspect modern
engines with OBD4 are cleaner than my propane system though.
An added bonus is that propane is currently 1/2 the price of gasoline.  I've
even got my old BMW on propane.
Pictures of the van at this URL
http://www.telusplanet.net/public/gary2a/rack/propane/propane.htm

Gary Lee
http://www.telusplanet.net/public/gary2a/rack/vanagonrack.htm