Military-Vehicles: Re: [MV] What about oxygenated fuel?

Re: [MV] What about oxygenated fuel?

Jeff Polidoro (willys@vgernet.net)
Fri, 3 Oct 1997 14:06:19 -0400

> Alan Bowes wrote:
> > snip...
> >
> > This is required in certain U.S. metropolitan areas (some 35 or 40
areas, I
> > believe) during winter months, when temperature inversions tend to
concentrate
> > CO and other emissions, when engines tend to run richer for a larger
percentage
> > of the time due to the lower temperatures, and when more fossil fuels
are being
> > burned
> > for heating purposes.
> > snip...
>
> Alan,
>
> Why would engine run richer when the weather is colder? Colder air
> is more dense, therefore I would expect the engine to be running leaner
> during the Winter than the Summer, therefore have less of a CO problem
> (once at operating temperature).
>
> Am I missing something?
>
> I still don't really understand why, when considering modern cars with
> fuel injection and exhaust gas oxygen sensors, why they even bother
> with oxygenated fuels since feedback systems within the cars (mass air
> sensors on intake air, etc) keep them burning properly regardless of
> environment. It is only owners of "antique" vehicles (like members
> of this group) who see "cleaner" exhaust through use of these Winter
> fuels (albeit at the expense of soft fuel system parts).

> Darren Allen

I would easily crack under the pressure of trying speak for "Professor"
Bowes but speaking for myself, I would say that even with the electronic
choke of the CC engines a considerable rich or over-rich condition exists
during cranking and at idle due to the settings of the engine management
system, continues through warm-up until operating temperature is reached,
which may never occur, depending upon load and duration of trip, that
optimum (for emissions) cylinder temperatures are rarely reached in colder
climates regardless of load, (Look at all the trucks with their radiators
completely or partially closed off by winter fronts and shutters, while no
equivalent exists for automobiles.), and that even though the air is more
dense, the fuel is more dense, as well.

I'd have to think about it (or just ask Alan) but the proportional
difference might actually favor the gasoline because while its (the fuel's)
density would be due to the difference in the two ambient temperatures the
intake charge would have already been below ambient due to it cooling as it
speeds up to pass through the throttle blade restriction, so the percentage
decrease in temperature would be lower. While they both might drop the
same number of degrees, it would be from a different baseline and,
therefore, a lesser percentage for the air, resulting in a richer mixture.

Although I feel we're all in this together and should do what we can to
reduce emissions, I drive across to NY (State, not City) to use
unoxygenated fuel. In my 94 Chevy pickup it is almost exactly a 10%
difference in fuel mileage (22/20), which leads me to believe that although
there is a percentage reduction in CO emissions, there may very well be an
increase in absolutes. Not to mention the increased consumption and cost.
I guess if I was convinced there was a net gain, somewhere, I'd use the
stuff but I just don't see it and, IMHO, it's death on small engines, chain
saws, in particular.

JP

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