Jim,
While I don't know for certain (I'm a young whipper-snapper, so I
don't remember the pre-catalyst era all that well), I think the key was
in a previous e-mail response from Larry Hoy and a side-effect of
carburation. The higher thermostat will ensure that the coolant will
get up to a certain temperature more quickly. This coolant will heat up
the intake manifold quickly which will reduce the chances of fuel
puddling and condensing in the (previously cold) manifold and then
dripping into the combustion chamber. Liquid fuel in the combustion
chamber won't burn properly and will produce harmful emissions, and as a
side note, will drip past the rings and thin out your oil on the chamber
walls and increase the occurrence of the rings scoring the sleeves. In
fact, that's the only reason that coolant passes through the intake
manifold at all. So another engineering trade took place in Detroit:
The higher thermostat set-point and hotter coolant may have
theoretically increased the NOX byproducts of combustion, but it
shortens the period of time that the car was running rich and producing
very real emissions. This is why cars run cleaner after warming up. It
is not directly related to combustion, but is an artifact of our intake
design and the limitation of carburetors and throttle-body fuel
injection. Multi-point fuel injection also runs cleaner after warming
up a little, but this is because it takes a few minutes for the O2
sensor to warm up in the exhaust stream, allowing the computer to run in
closed-loop mode and go for that sacred stoichiometric mixture. Some O2
sensors can heat up in a few seconds, but they don't operate over a wide
enough set of exhaust conditions to be ideal (another trade, although
perhaps a bad one?).
Keep in mind that gasoline, in theory, should burn and produce
nothing more harmful than water and carbon-dioxide. But because we
don't give it enough time to burn completely, it produces all that other
harmful crap. Drop a match in a puddle of gas (no, don't!.... I'm just
making a point) and it will actually burn quite clean. Thrust a lighted
match quickly into a tank of gas below the 'water line' and nothing will
happen at all (saw a professor do that once.....ONCE!) But if you
hesitate above the gasoline, the vapors go kaboom! I wonder if Prof.
Austin is still terrorizing freshmen? Funny, I don't ever remember
seeing him have eyebrows or arm hair....... coincidence??
But I digress, as for your other question, I believe it is the NOX
emissions that go up as combustion temp goes up. I think that the CO,
and the third one (escapes my mind, what its called) go down, but I
could be wrong on that one. Any chemists in the group?
Ciao!
James J.
bown wrote:
>James J.
>Thanks for the excellent response. You should write text books!
>I am curious about your comment concerning emissions.
>
><James J. wrote> "I should mention that hotter temps mean higher emissions,
>too."
>
>Back in the old days it seemed like 180 F thermostats were the norm.
>Then when emissions became an issue 192 F thermostats became common.
>I was told that the higher temp thermostats were to help reduce emisisons.
>Any insight into this?
>Regards,
>Jim B.
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