jcnel_evo8

iTrader: (2)

Hi all,

In the small valley where I live, there is a big push to clean up our cars, and one of the ways is through emissions testing. My understanding is the most harmful substance in emissions are Nitrogen Oxides called NOx.

Being that the EVO is eventually very shortly going to be modified, this is a definately worry. I'm seeking more information on this emissions equation.

It is my understanding NOxes are formed when combustion temperatures rise above about 2500degF, and all the oxygen is not burned by the gas. This happens when the engine is run close too the magic 14.7:1 air/fuel mixture as the some oxygen is not burned with the fuel, it gets linked with the Nitrogen gas in the air, making NOx.

Modern day cars, including the EVO, have a three way catalytic converter that if in its "operating temperature range" will strip the Oxygen from the Nitrogen and make relatively harmful N2 and O2.

At idle, the combustion becomes cooler, and the NOxes also go away, which is good.

Does the catalytic converter also stay within its operating temperature range at idle?

Thanks in advance for any answers.

jcnel.

jcnel_evo8

iTrader: (2)

bump

xtnct

iTrader: (33)

Yes, catalitic converters also work at idle, once they reach their operating temp.

MalibuJack

iTrader: (5)

Yep.. Catalytic converters do work at idle, and are designed to accomodate the flow it would see during daily driving in closed loop operation.. As soon as the flow of exhaust exceeds that, the emissions go up (Thats why alot of emission testing uses that rolling road test on the dyno) and so do the ratios of fuel, and air, and therefore the different emissions change... Fortunately most cars don't spend most of their time at WOT where a Cat would have pretty much no affect and it just becomes a restriction.

Most people don't realize that increasing the size of your cat and lowering restrictions, results in raising emissions at idle and daily driving unless there's adequate backpressure to allow the gasses to permeate into the converter and not just pass through it.

The good news is that as long as your car is running well and tuned properly, and closed loop operation is working, You could likely pass an emission test in most states even without a catalytic converter (besides being visually checked) The exception is cars with larger cams that have a pretty significant overlap since you get unburned fuel into the exhaust charge which would end up raising your EGT's increasing NOx emissions.

Nothing like a little science to throw a monkeywrench into things eh?

Creating power is about using energy efficiently, and being clean is also about being efficient.. So you can have power with being clean, its just something that takes a little more time since you do have to take these things into account.

mifesto

iTrader: (58)

so in another words.. its good to go abit lean for NOx testing hehe

jcnel_evo8

iTrader: (2)

Actually no ... its not good to go lean for NOx, the leaner the mixture the potentially hotter the combustion becomes, and that produces NOx. Nitrogen doesn't want to easily combine with Oxygen, which is one reason we can run our internal combustion engines. Combustion of Gasoline and Oxygen is a lot lower in temperature. However, once the combustion reaches a high temperature, and is lean, that means there are no more hydrocarbons to combine with the Oxygen, the Nitrogen is the next likely canadate, and that's why we get NOx emissions.

As far as catalytic converters go ... I spoke with a professor that is the chair of urban development, and does smog type work for OEM manufactures, and he said (without being able to give me anything to look up) catalytic converters do cool off significantly enough at idle to pump out a significantly higher amount of NOx when you start off the line again, than if you were driving steady state.

This is a call for me to whip out my thermocouples and try to empirically characterize the temperature of a cat. The optimum would be to place a probe on the catalyzing element(s) itself, but drilling my cat might be hard to put a plug in to keep gasses from wanting to exit there, and later bring the cat back to stock. If I'm careful, I might be able to weld a bung, like an O2 sensor bung, and screw in a probe ... but what I really want to do is put the probe on the element itself and see its temperature profile.

Thanks all, for the insight.

Cheers,

jcnel.