Emissions

[JimX]

There's a lot of talk everywhere about emissions lately, and even the current model MX5 has dropped a bit of power in order to meet some new emissions standard.

What I want to know is, why are emissions so hard to control? Aren't the "emissions" just unburnt fuel? I would have thought that if you improved the ignition and maybe ran a better quality catalytic converter with a good O2 sensor that it shouldn't matter how much power you're running. If all the fuel is burnt you should in theory be able to run mega horsepower and not worry about emissions.

So anyway, it doesn't seem as simple as that or it wouldn't be such a concern. Can someone explain why it's so hard to control them?

[hitnrun]

Hi JimX,

From what I understand, it's not just unburnt fuel. Hydrocarbons, and various other crap are made from the combustion of the engine. Usually unburnt fuel isn't so much of a problem. Also remembe rthat as you car developes more power, you are creating more waste. High fuel usage simply make more crap.

In Japan, emission testing is done at low RPM and load, so even poorly tuned cars can pass. In Australia, the testing of emissions is extremely strict, therefore your car needs to be in good tune before it will pass.

With regards to emissions being hard to control their are, all new engine have (usually) very high levels of compromise (sp?) to accomodate NVH and emissions. They are also much better desinged, so we usually see a better engine anyway.

If you take a look very *very* serious drag cars etc, the will usually modify the engineering extensively, as they have no need for emissions control, road reg etc.

In the end, having a car tuned properly, with a new or clean cat. should pass all emissions.

Some of this stuff is very general, and or slightly wrong, feel free to correct me.

Regards,

Tim

[blind_elk]

Its really about the products of the combustion process. Ideally, when you burn gasoline - which is basically carbon and hydrogen - you should get CO2 and Water as the products. However, if you burn it in the presence of Nitrogen (which is 80% of air), then you get oxides of nitrogen (NOx) which is ultimately responsible for smog. And the spark that ignites the air/fuel mixture can cause the oxygen to convert to ozone.

Other chemical, rather than combustion, reactions occur, producing nasties like benzene.

If the fuel mixture is too rich (not enough oxygen) then you get CO instead of CO2.

Then you add in impurities in the gasoline like sulphur compounds, which undergo changes to produce oxides of sulphur (SOx), which can dissolve in water to produce sulphuric acid ("acid rain").

The catalytic converter is primarily there to chemically alter the NOx and SOx compounds.

So you see, its a lot more complicated than simply controlling the amount of unburnt fuel coming out the exhaust pipe.