PHILIPPE TUSLER wrote:
> Well, Tintin has just failed his third pre-check. I got the hydrocarbons
> way down, the the CO is way up and nothing I
> do seems to have any effect. No seems to be able to tell me what
> affects CO emissions.
Quick answer, the richer the mixture the higher the CO.
Lean out the carbs as much as possible, or better-introduce more air-
like pull off an air cap or something.
Long answer, to quote the excellent book "Introduction to Internal
Combustion Engines, 2nd ed." by Richard Stone, published by the Society
of Automotive Engineers (SAE), "Emessions of CO, NOx, and HC vary between
different engines and are dependent on such variables as ignition timing,
load, speed, and, IN PARTICULAR (caps mine), fuel/air ratio. .....
Carbon monoxide (CO) is most concentrated with fuel-rich mixtures, as
there will be incomplete combustion. ..... Furthermore, the methods used
to reduce NOx tend to increase CO and HC emissions and vice versa. .....
Figure 3.15 shows typical variations of emissions with fuel/air ratio
for a spark ignition engine."
Now I will try to describe figure 3.15....
In the middle of the graph is "1.0" which is the ideal air/fuel ratio,
with 0.8 and 1.2 on the ends. This basically is representing %20 lean to
%20 rich with ideal in the middle. At 1.0 the CO volume is approx. %0.5.
At just %5 rich (1.05) the CO volume is %1.5. At %15 rich (1.15)the CO is
way up to %4.0 volume, or in other words, even the slightest rich mixture
will gain a big jump in CO. From ideal (1.0) to just %10 rich the CO
volume is nearly three times as high.
So let me sum up the highs and lows of the fuel/air mixture in relation
to HC, NOx, and CO.
HC- highest at %15 rich and at %15 lean
lowest at %10 lean
(a 'U' shaped line)
NOx- highest at %5 lean
lowest at %20 lean and %15 rich
(a 'n' shaped line)
CO- highest at %15 rich and above
lowest at %5 lean or less
(a 'J' shaped line)
So if you want the lowest of all three, the 'ideal' fuel ratio is best,
approx. 14:1.
If you want low HC and CO, LEAN IT OUT, with %10 lean being the best.
If you want low NOx, the richer the better, with %15 being the best.
To get a 'feel' as to what these percentages mean, %20 lean is about
as lean as you can go and still keep the engine running, same for %20
rich.
Now I'm tired of typing, so I won't quote the book directly, but
this book seems to imply that it is better to reduce CO and HC (having
a leaner mixture) by introducing more air to the engine rather
than lowering the fuel rate. Or in other words keep the fuel the same
but get in more air, so slip a vacuum hose off or something.
Leaning out via more air is better for NOx (goes up less), for some
reason.
I can go further, or even muddy the waters more, if you want.....
-Aron Travis-
"always in a automotive frenzy"
P.S. You Brit's and Euro's pay attention, this crap is comming your way,
so watch out to what happens here in America, and California especially.
The STATE is getting overly concerned about emissions and classic cars.
P.P.S. Remember all that emission stuff you pulled off the car and
threw away? Moss would love to sell you a air pump for $295.00.
I wonder how much it will cost when all states require one? ;o)
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