switching mechanism in emissions control
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Why am I here ?
Joined: May 2002
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From: Boston, MA
switching mechanism in emissions control
What follows for S4 NA but should be same for other types
Why is there a switching mechanism in emissions control ?
Having fresh air go to the CAT directly via the split air pipe or having fresh air go the CAT indirectly via the exhaust ... What difference does it make really (the CAT gets the air anyways, right) ?
Why not have the pumped air go to the exhaust port with no switching mechanism ?
I assume there must be a good reason but I don't understand what it is.
hugues -
Why is there a switching mechanism in emissions control ?
Having fresh air go to the CAT directly via the split air pipe or having fresh air go the CAT indirectly via the exhaust ... What difference does it make really (the CAT gets the air anyways, right) ?
Why not have the pumped air go to the exhaust port with no switching mechanism ?
I assume there must be a good reason but I don't understand what it is.
hugues -
Locust of the apocalypse
Joined: Apr 2003
Posts: 2,553
Likes: 2
From: Directly above the center of the earth (York, PA)
Its all EPA voodoo science...
Basically, Mazda engineers looked at the relative emissions rates of the rotary engine and the performance of the cats and set up the valving to compensate for exhaust loading at different RPM's / engine load parameters.
It all has to do with oxygen. The cats use Oxygen in the air to react the exhaust gasses with the metals in the cats. Air is injected directly into the cat to increase the oxygen content to make the reactions more efficient. Air is injected into the exhaust stream before the cats to "thin out" the mix before the exhaust hits the cats and drowns it out. The more oxygen in the exhaust gas, theoretically, the less is needed by the cats, also, as flow increases, different demands are placed on the system.
I sat through training classes in this when I was working for Air Quality in DEP, and it made sense at the time, but,
AS to where the air is injected and when.. I haven't a freakin clue but it relates directly to the gas loading in the exhaust stream and it was good enough to convince EPA that it worked when it was originally designed!!!!
Basically, Mazda engineers looked at the relative emissions rates of the rotary engine and the performance of the cats and set up the valving to compensate for exhaust loading at different RPM's / engine load parameters.
It all has to do with oxygen. The cats use Oxygen in the air to react the exhaust gasses with the metals in the cats. Air is injected directly into the cat to increase the oxygen content to make the reactions more efficient. Air is injected into the exhaust stream before the cats to "thin out" the mix before the exhaust hits the cats and drowns it out. The more oxygen in the exhaust gas, theoretically, the less is needed by the cats, also, as flow increases, different demands are placed on the system.
I sat through training classes in this when I was working for Air Quality in DEP, and it made sense at the time, but,
AS to where the air is injected and when.. I haven't a freakin clue but it relates directly to the gas loading in the exhaust stream and it was good enough to convince EPA that it worked when it was originally designed!!!!