How is the coolant temperature related to the increase exhaust emission?


http://www.forparts.com/emission1.htm

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...In addition to clogged air filters, defective intake manifold vacuum, throttle position, coolant temperature, inlet air temperature, and mass air flow sensors can increase exhaust emissions.

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1987 MB260E 187K

Because it effects air/fuel mixture & ignition timing.

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2007 C 230 Sport.

In one word, NoX. The higher your engine temperature the more NoX produced. The green house gas is produced when the combustion chamber temperature exceeds 1500 degrees (might be 2500) 25 to 40 degrees F over proper engine temperature will more than likely produce a large amount of NoX gas.

Had a friend that had low flow through the radiator yet it was undetectable on the temperature gauge! Up a steep road could have tipped him off to the problem but not on the flats in Ca. in the winter. Measured aprrox 2100 NoX before radiator was rodded than 500 NoX after...WOW!!!


My .02 fwiw

The higher the coolant temperature the lower the engine out HC. Coolant temperature has little/no effect on NOx or CO.

As the 4500 degree flame front approaches the combustion chamber boundaries it is quenched because the surfaces are cool relative to the flame front, but the higher the boundary temperature the less quenching occurs.

CO formation is primarily dependent on fuel-air ratio, and anything richer than stoichiometric dramatically increases CO in proportion to the excess fuel.

NOx is formed in the 4500 degree flame front. Cooling the peak flame front temperature by either retarding the timing or diluting with fresh charge with inert exhaust gas lowers peak flame front temperature and NOx formation.

Duke

FYI, only carbon dioxide CO2 (or less commonly called "carbonic gas") is called "the green house gas".

Carbon and nitrogen can combine with oxygen to produce various kinds of oxides in gaseous form (at standard conditions of 1 atm and 25 Celcius):

2C + O2 -> 2CO (carbon monoxide)
C + O2 -> CO2 (carbon dioxide)

N2 + O2 -> 2NO (nitric oxide)
N2 + 2O2 -> 2NO2 (nitrogen dioxide)

There is also another oxide of nitrogen called "dinitrogen trioxide". However, dinitrogen trioxide only exists in liquid form at low temperatures and is very unstable (converting back to NO and NO2) at standard conditions. It is formed from the reaction of NO and NO2:

NO(g) + NO2(g) -> N2O3(l)

Actually, there's yet another oxide of nitrogen called dinitrogen pentoxide N2O5 which exists only in solid form. It's also very unstable.

Since N2O3 and N2O5 are usually only produced in laboratory conditions, they have nothing to do with exhaust gas problem.


The reaction between carbon and oxygen is relatively easy to happen (such as coal burning or hydrocarbon combustion in SI or CI engines etc.) However, the reaction between nitrogen and oxygen requires VERY high temperatures to take place. Chemically speaking, nitrogen gas (N2) is a relatively unreactive/inert gas even though it does not belong to the noble/inert gas group (such as helium, neon, argon, krypton etc.)
That chemical inertness explains why nitrogen gas constitutes almost 79% of the current atmosphere (the remaining 20% consists of 20% O2, 0.03% CO2 and tiny amount of other gases)

Nitrogen oxides (NO, NO2) are only created under relatively extreme conditions, such as volcanic eruptions, lightning (high voltage), and very high temperatures in internal engine combustion. When the temperature is not too high, nitric oxide (NO) is produced, but too high temperature (like 4500 degree flame in Duke 2.6's post) will produce nitrogen dioxide (NO2).

In internal combustion process, CO is produced when that the fuel/air mixture ratio is more than the chemically stoichiometric ratio, i.e. not enough oxygen is available to completely convert CO into CO2.

There's a funny difference in oxides of carbon and nitrogen. For oxides of carbon, CO is very toxic because of its extremely high affinity to the main oxygen-absorbing component "hemoglobin" of red blood cells (erythrocytes). From a physico-chemical standpoint, CO's affinity for hemoglobin is 4 times (yes FOUR times) higher than that of oxygen for hemoglobin. Once you are exposed to CO, your blood will suck it in like a leech and it stays attached to hemoglobin for a long time, even when oxygen is available. Therefore, CO is a very dangerous gas while CO2 is not.

However, NO is not dangerous while NO2 is. NO2 affects the throat and lung in a damaging way. Prolonged exposure to high levels of nitrogen dioxide (NO2) can seriously affect the ability of blood to carry oxygen, causing dizziness or even respiratory failure. In Mercedes cars, the EGR device is used to dump a portion of lower temperature exhaust gas back into the combustion chambers to lower the flame front temperature, thus reducing the production of NO2. The catalytic converter also has special catalysts to reduce NO2 to NO, for which the released oxygen is used to convert CO in the exhaust gas into CO2, and burn off the excess hydrocarbon.

Even though NO is not as dangerous as NO2, it can be oxidized further in the atmosphere to produce NO2. Also, both NO and NO2 are major components of photochemical smog (very easily observed in the Los Angeles area). NO2 causes the smog to have the yellowish-brown color of the smog. When combined with water (H2O), NO2 will produce nitric acid (HNO3) - a very strong and extremely corrosive acid.

For these reasons, internal combustion process must be controlled in such a way that limits the production of NO and NO2 to a minimum level. Catalysts can reduce NO2 to NO, but cannot convert nitrogen in NO and NO2 back to its original gaseous form N2, so the EGR must be present to help lower the flame front. By lowering the temperature enough to an appropriate level, very little NO and NO2 will be created.

In order to keep the extremely dangerous carbon monoxide CO to a minimum level, the ECU and its oxygen sensors will constantly monitor the oxygen content of the exhaust gas and automatically adjust the fuel/air intake mixture as well as the timing for more complete combustion. The catalysts in the cat is a car's final line of defense to convert most CO to CO2.

Eric