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Re: ALL gasoline powered internal combustion engines...
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Posted by Justin VanAbrahams [Email] (#32) [Profile/Gallery] (more from Justin VanAbrahams) on Tue, 28 Aug 2007 19:42:17 Share Post by Email
In Reply to: ALL gasoline powered internal combustion engines..., David in Tallahassee [Profile/Gallery] , Tue, 28 Aug 2007 14:45:39
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I might be sticking my foot in my mouth, but I'm pretty sure that catalytic converter technology hasn't changed much in the last twenty years or so. It's the same substances inside, doing the same job. In some cases, the material that composes the matrix may have changed from ceramic to metallic, but rhodium and platinum are what's used inside and have been since the '70s.

Whether a car has a single 3-way cat or a series of n-way cats depends largely on the emissions profile of the engine in question, and how the output of the first cat will affect the performance of the second. The whole thing is a balancing act, and there is as much science as art here - for example, some manufacturers choose to run a richer mixture and incorporate a leading cat for dealing with HC emissions before a second 3-way cat deals with the final product.

My understanding is that with the exception of multiple n-way systems where each catalytic converter may have a focus specific to an engine, your run-of-the-mill 3-way cats used on most every modern car is the same regardless of whether your car is old or OBD1 or OBD2 compliant. What makes a generic cat different from an ODB2 cat isn't anything more than a bung for a second O2 sensor and a paid-for government certification. Nothing special on the inside - the same guts. Swapping a non-OBD cat in place of an ODBII cat won't affect your emissions one bit.

As for passing modern emissions without a cat - good luck on that. It may be true in the midwest, but out on the coast where many (if not most) states are adopting California's emissions standards or imposing their own higher standards, there is no way a car could pass emissions without a converter. The NOx emissions alone prevent that from happening - a catalytic converter is the *sole* method for getting them out of the exhaust stream enough to meet standards.

Related, a catalytic converter absolutely removes substances from the exhaust stream, and more than one of them. A standard 3-way catalytic converter uses platinum to accelerate oxidation of HCs to CO2 and water (1 way), and the rhodium breaks down NOx emissions into its component nitrogen and oxygen (2 way). The now-free oxygen and CO combine to produce CO2 (3 way). If you would rather enjoy the smog and acid rain from the otherwise emitted HC and NOx instead of CO2 and water, well, that's cool for you. I'd much prefer to eliminate those particles as much as possible, and that's precisely what a catalytic converter does.

I'm not a science guy, but this is stuff I've read from numerous sources, including my handy-dandy Guide to Automotive Emissions Equipment.

posted by 75.45.108...


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