Oh boy, once again we are talking about something that I can at least offer
an opinion based on years of sleeping through college courses. Why is it
that they always offered the most technical courses at obscenely early
hours? I guess they were just trying to hasten the conversion to full
geek.
To date most pollution testing concentrated on carbon and hydrogen
compounds. In particular hydrocarbons from unburned fuel and carbon
monoxide from incomplete combustion. To control these you decrease fuel
and increase heat. Warm the intake air. Retard the ignition to heat up
the exhaust. Inject air into the exhaust ports. Lean out the engine until
just above the lean limit- if it misses then it HC will increase again.
All of these decrease CO and HC emissions. So in order to pass emissions
you just lean the sucker out and retard it until it barely runs and limp to
the test station.
Oxides of nitrogen, on the other hand, occur when heat and pressure cause
the nitrogen in the air to combine with the oxygen in the air. So,
everything you do to reduce HC and CO output increases NOx output. NOx in
the atmosphere reacts with water and forms nitric acid- a key ingredient in
acid rain. CO also form an acid -carbolic acid I believe- when combined
with water and is the other key pollutant for acid rain.
The main weapon for fighting NOx was exhaust gas recirculation. EGR adds
inert exhaust gasses to the combustion gasses under low load situations
(cruise, idle) to reduce the peak temperatures and reduce NOx. Of course
now days they just dump everything into a 3-way catalyst and call it a done
deal.
So to make a long story at least somewhat meaningful, The catalytic
converter will probably be needed now to pass emissions. In itself, the
cat does not help NOx. However, it does allow the engine to run under
conditions that reduce NOx then swats the leftover HC and CO in a lower
temp and pressure environment where more NOx will not form.
For HC and CO, air injection is the most important device on our cars AS
LONG AS NOx IS NOT MEASURED. Once NOx is controlled, then the whole thing
becomes much more complex and everything has to be in tip-top condition to
pass the tests.
Solution? Buy an MGA of course! But seriously, I truly expect that in
the next few years retrofit EFI/ 3-way cat systems will become cheap and
available as these types of laws get more and more common. But that's just
me.
Regards,
Bill Eastman
61 MGA completely free to pollute as it sees fit. Is that a good thing? I
don't know.
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