oder, they got poorer fuel mileage than catalytic converter engines, but you
knew that didn't you? they also sold poorer partly because of their poor fuel
mileage and more so because they were maintenance hogs. but you knew that,
didn't you?

are you *still* claiming that oxygenated gasoline exists because those carb'd
engine -- few in number -- needed special fuel upon warm up, AND the EPA wanted
to accomodate the car manufacturers?

yeah, sure. whatever you say.

(modervador)
Date: 9/29/2004 11:07 AM Eastern Daylight Time
Message-id:

(JAXAshby) wrote in message
...
Reduction of CO emissions during warm-up for carbureted engines.


mum mum vador, knock it off. for all practical purposes there are no
carbueted
auto engines on the road for a very long time. I believe that last such
sold
as new was the miserable CVCC engine, and that was well more than 25 years
ago.

The carburetted CVCC engine's last year was 1985. By 1984 it was
running closed-loop with feedback from an O2 sensor in the exhaust
stream to maintain a stoichiometric mixture, so the "lean burning
stratified charge" feature of the original CVCC was no longer being
used although the head retained the pre-combustion chamber and carb
retained the auxilliary 3rd barrel to feed the prechamber. The
prechamber and 3rd barrel were done away with for 1986. The last year
for the standard carbed Accord engine was 1989 (injection was an
option starting in 1985) and the Civic models all got fuel injection
in 1988 I think.

But that's just the Hondas. There were plenty of other carbed engines
made which are still around, both open-loop and closed-loop, and I
don't care to dredge to find when the last one was sold new in the
U.S., but it was more like 14 years ago and it likely wasn't a Honda.
There are also open-loop fuel injection systems (no O2 sensor).

With open loop, before the engine warms up, combustion is less
controlled and the choke (or idle enrichment in FI) makes it run
slichtly rich, increasing CO output. Even with closed loop, the design
of the O2 sensor and engine management system is a factor. The O2
sensor does not send out a signal till it warms up, so the engine
management system must run in open-loop mode till then, defaulting to
slightly rich with elevated CO output. Many O2 sensors have a heating
element to speed the warm-up of the sensor to decrease the time
running open-loop. But then there's the catalytic converter, the final
link. Till it warms up, it allows the CO to escape unconverted. Some
catalytic converters are being designed to have heaters that decrease
warm-up time.

So even the most modern car has some period after a cold start, during
which it runs open-loop and spews more CO than it does after warm-up.
Oxygenated fuels increase the oxygen-to-hydrocarbon ratio during
open-loop running and thus promote more complete combustion that
produces CO2 rather than CO. In several metropolitan areas there
remains a high proportion of older cars with carbs and early-version
fuel injection systems. In winter months the warm-up time is increased
during which these cars emit increased CO to an extent large enough
that the EPA (or some other branch of gummint) has mandated oxygenated
fuels during the coldest months in these areas.

%mod%