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Can a new vehicle from a plant be produced without a catalytic converter? Is it possible? I am a lecturer at a college in Zimbabwe, and my students recently asked this question, so I am researching.

donjuedo
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Charly K Mwamber
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  • absolutely possible, it is just for converting the 'warming-up' emissions from your engine. Typically a 'cat' is expired after 12 months of use anyhow (the active component gets used up) & simply becomes another exhaust-restricting device. It is somewhat common in Australia for older cars to have the 'cat' bypassed or removed to help with economy (practical, yes. Increased emissions, no. illegal, yes.) – RozzA Jun 05 '19 at 21:15
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    @RozzA "it is just for converting the 'warming-up' emissions from your engine." Are you sure about that? Wikipedia says, essentially, the exact opposite: that most of the emissions from cat-fitted cars come in the first few minutes because the cat is ineffective until it's warmed up enough. And the whole point of a catalyst is that it isn't used up: it merely facilitates a chemical reaction. So the other claim in your comment sounds very dubious, too. – David Richerby Jun 05 '19 at 21:28
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    @RozzA Not true - catalysts do not get "used up". It certainly is possible to poison a catalyst with leaded fuel, but that only needs a few trips at most to kill the cat. Most countries following CARB, EURO or similar emissions rules require regular emissions tests, and it simply is not possible to meet those emissions standards without a cat and any other related emissions control devices. FYI, I'm an ex automotive software engineer who's spent far too many years dealing with emissions and diagnostics specifications! – Graham Jun 05 '19 at 22:28
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    @Graham - While I completely agree with you about catalysts not getting used up (a catalyst by nature does not get used up ... it just causes a reaction), you're aren't technically right about a vehicle NOT being able to pass emissions without a cat. Most emissions places here in the states only plug into the DLC on OBDII vehicle and look to see if the vehicle has passed its own diagnostics (drive cycle) to check emissions. All you have to do is tune your ECM to never cause any issues and you're golden. – Pᴀᴜʟsᴛᴇʀ2 Jun 06 '19 at 00:30
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    @Paulster2 Remarkably trusting of them. In the UK they stick a probe up the exhaust. Of course it doesn't catch everything, but it reduces the options for cheating, at least for petrol (gasoline) - diesel emissions are mostly particulates and can't be tested so easily. As for "all you have to do", it's not necessarily easy to do that (depending on the ECU of course), or at least to do it in a way which the tester won't pick up. – Graham Jun 06 '19 at 01:06
  • And some countries have differing requirements for emissions. A percentage concentration may require a catalytic converter, but emissions per km will not, for a small enough vehicle. And of course EV's don't have them at all, nor do some fuels such as Hydrogen. – mckenzm Jun 06 '19 at 05:05
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    @RozzA no, that's just some nonsense made up by hotrod types to rationalize hacking the cat off the car... My cat was effective for at least 15 years... – Harper - Reinstate Monica Jun 06 '19 at 14:23
  • @Graham not that trusting, at least with respect to meddling end users. There is also a visual inspection component where hacks like shimming O2 sensors is apparent. AFAIK the ECU is also on the list of items that can only be replaced with approved items. Plus few people replace ECUs, if you even have that option for a particular car. The up side is that you get much better emissions testing. The probe only checks emissions at idle. The car can test a handful of different scenarios, including when the engine is under load. This is also why we have an OBDII port at all. – Adam Jun 07 '19 at 01:15
  • My car never needs a cat. (EV driver, of course) – Carl Witthoft Jun 07 '19 at 14:35
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    @CarlWitthoft No, but your power plant probably does! – David Richerby Jun 07 '19 at 15:30
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    @Adam Though most people do not replace an ECU/PCM, some manufacturers are pretty lax about end-user updates. My experience is with GM - and I can say for certain that any updates that I did to the PCM remained unnoticed by emissions testers. For OP - many states allow race cars to go catless and in some circles, converting a road vehicle to a track car does, indeed, involve removing the cat. If buying a vehicle straight from the factory for race purposes, well, those are generally out of budget for most and I'm sure you can order whatever you want at that point. – Hueco Jun 07 '19 at 16:45

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You don't have to have an catalytic converter, they aren't required for the operation of an engine. Catalytic converters use chemical reactions to reduce the pollution in internal combustion engine exhaust, and are emissions control devices which are required by regulation in many countries. So it's technologically possible to build a car without one, it just may not be legal depending on where you are.

GdD
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    On top of that, electrical cars do not need one (for obvious reasons) and most marine engines also do not always require one – Horkrine Jun 06 '19 at 12:56
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That will depend on the market regulations for the target country ie which country that vehicle will be sold in.

Cars built to be sold in Europe & US have to meet stringent regulations as regards emissions so they are required to have a catalytic converter.

Other countries may not (yet) have that requirement, so a "cat"may not be necessary.

The large car manufacturers have been known to "use" this - when tighter emissions legislation came in in the Eu, some car manufacturers had stocks of engine that were no longer fit for the EU market. These were then sold in other markets...

Solar Mike
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    Of course the other answer to "Can a vehicle from a plant be produced without a cat" can be answered "Yes, an electric vehicle" (or a vehicle such as a racing go-kart) – Steve Matthews Jun 05 '19 at 12:14
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    @SteveMatthews you can fit a cat to an electric vehicle - as an ornament... Are some countries starting to require smaller engines go-karts, lawnmowers etc to meet higher emissions standards? – Solar Mike Jun 05 '19 at 12:15
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    @SolarMike: I know california has strict requirements for small engines, I'm not sure if it expands to requiring cats but their emissions are certainly a factor. – jesse_b Jun 05 '19 at 18:44
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    @SolarMike Even my 25-cc weed whacker has a cat in the US, it's a platinum coated mesh in the muffler. As Jesse_b mentions, it's because California is so sunny, they have photochemical smog problems. – user71659 Jun 05 '19 at 20:52
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    @user71659 And because of the geography of Western California, with mountains on one side and ocean on the other. This means that when photochemicals show up, they don't really have anywhere to go and so tend to accumulate into worse (more dense) smog than you would get in other places. – Mason Wheeler Jun 05 '19 at 21:00
  • This would be improved if you could find examples of regulations which specifically require a catalytic converter. While any particular code might be written such that a catalytic converter is explicitly required, the code would be better written to set maximum emissions requirements, rather than explicitly require any particular technology be used. I suspect that at least a considerable number of laws/regulations take the route of specifying maximum emissions, rather than explicitly stating any particular technology (i.e. a catalytic converter) must be used. – Makyen Jun 08 '19 at 00:41
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Yes, in theory. The government doesn't care how your engine hits the required emissions numbers. As an engine designer, you get a tabula rasa, and are free to build any system that will do the job.

Catalytic converters seem to be a winning choice for most if not all engine builders, because engine building is largely a costing game and cats are the easiest way to hit a price point. A big part of why they hit a price point is that they are already mass produced and readily available both in prototyping and in mass production at scale.

Harper - Reinstate Monica
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    Given their hobby to go against the market mainstream in almost everything, if it were possible to fulfill exhaust gas limits without a catalytic converter, Mazda would already be doing it :) – Pavel Jun 07 '19 at 09:16
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No Telsa has a cat. While you could bolt one to a Tesla it would serve no purpose.

Loren Pechtel
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