First, I'd like to reword part of an earlier comment to clarify a semantic
point:
I was speaking earlier about "maintaining the correct fuel-to-air ratio" as the
engine warms up. It is well known that a "richer" mixture is required when an
engine is warming up in terms of the VOLUME of fuel to VOLUME of air. However,
in terms of the relative number of fuel and air MOLECULES, I believe that the
fuel/air ratio should be about the same when the engine is cold as as when the
engine is warmed up, due to the fact that the extra fuel (richer mixture) that
is used during warm-up is made up for by the extra air molecules packed into
the same volume of colder, denser air in the combustion chamber.
Next point:
Many older vehicles have carburetors with either manual or automatic chokes.
These are not very efficient or accurate devices, and there is probably a
tendency to run an overly rich mixture to avoid any "flat spots" when you step
on the throttle. This means that in terms of CO reduction, these vehicles can
benefit even more from using oxygenated fuels during their warm-up periods than
more modern vehicles that maintain a more accurate fuel/air ratio. But make no
mistake, all vehicles use more fuel (richer "volumetric" ratio) during their
warm-up period, thus putting out more total emissions during warm-up, and.all
vehicles put out less CO with oxygenated fuels.
Next point:
Some further explanation of why oxygenated gasoline works to reduce CO
emissions: When extra oxygen is packaged in the fuel itself, the fuel requires
less oxygen from the air in the combustion chamber during the combustion
process. This is analogous to a "leaner" fuel/air mixture, without actually
reducing the volume of gasoline used. Carbon monoxide is produced when there is
a lack of sufficient oxygen in the combustion process. The extra oxygen in the
gasoline means that instead of CO, more CO2 is produced. It might also help
make the catalytic converter more efficient. Speaking of catalytic converters,
it is also worth mentioning that these, like engines, require several minutes
to warm up to the point where they are operating efficiently. This adds to the
amount of pollution created during winter months.
Finally (for now):
One minor drawback to oxygenated fuels that I forgot to mention before is that
they generate less power...perhaps because the energy potential of alcohol or
ether by volume is less than straight gasoline.
Alan
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