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Charlescrown wrote:This helps make sense of what happens. http://www.omnagen.com/nox-emissions.html

that article states 1500 degrees c most combustion chambers run at 550-700 degrees c NOx the ones the manufactures are concerned about can be produced from 300-800 degrees c. 1500 c would be a serious failure pistons and cylinder heads would go soft (melt so to speak) and fail below that temp I can melt alloy engine parts at 1200-1300c for casting.

Your looking at exhaust temperatures. Hey if you produce NOx at 300 degrees how the hell can you reduce it with a EGR valve? Have a look at this chart http://www.alentecinc.com/papers/NOx/Th ... %20NOx.htm

Charlescrown wrote:Your looking at exhaust temperatures. Hey if you produce NOx at 300 degrees how the hell can you reduce it with a EGR valve?

Because you are mixing in exhaust that doesn't contain any "free" oxygen and displacing intake air/fuel mix that does.

MAGP wrote:

Charlescrown wrote:Your looking at exhaust temperatures. Hey if you produce NOx at 300 degrees how the hell can you reduce it with a EGR valve?

Because you are mixing in exhaust that doesn't contain any "free" oxygen and displacing intake air/fuel mix that does.

MAGP nailed it the oxygen that is combusted becomes carbon monoxide and carbon dioxide it is the free oxygen that is the problem so it is displaced with exhaust gas. think of it this way you have 14 pars air 1 fuel to make x amount of power being demanded from the user that is 15 equal parts your chamber may be able to hold 20 of these parts so you add 5 parts of exhaust gas to limit the chance of NOx being produced. this is in a perfect world where all things are perfect but you get the intention.

Looks like we can't agree on the role of the EGR valve so I have no problems with that. I know its there to pull down the peak and I say peak temperatures in the combustion process and in doing so reducing the amount of NOx produced. We are talking well over 1000 deg C. Displacing oxygen simply means we need to push a little harder on the accelerator pedal to maintain the same speed. Nothing gained there.

I agree that EGR is to reduce combustion temperature and in turn reduce NOx production.
A charge consisting of gas with 21% oxygen, 78% nitrogen, a small amount of inert gas and an amount of fuel to make it stoichiometric will burn faster and hotter and create more NOx than a mixture with say 18% oxygen, 60% nitrogen, 20% inert exhaust gas.
A charge with EGR may still produce NOx at 300 degrees but peak temperature will be lower, NOx will be much lower, and the NOx that is created will be dealt with by the catalytic converter.

The problem with a car is the higher levels of NOx are produced it high temperatures. The amount produced at low temperatures is negligible. Manufacturers have been putting these things in since 1976 and it is the high temperatures they have been concerned with. As I said in my first post a good 3 way cat (I didn't add 14.7:1 fuel mix) will be more than whats required. Exhaust gas is around 700 deg C so it makes no sense putting it back into the combustion chamber if your looking at 300 deg.

Charlescrown wrote:The problem with a car is the higher levels of NOx are produced it high temperatures. The amount produced at low temperatures is negligible. Manufacturers have been putting these things in since 1976 and it is the high temperatures they have been concerned with. As I said in my first post a good 3 way cat (I didn't add 14.7:1 fuel mix) will be more than whats required. Exhaust gas is around 700 deg C so it makes no sense putting it back into the combustion chamber if your looking at 300 deg.

You have totally missed the point. By having an EGR the available "free" oxygen is less than with no EGR thus the amount of NOx produced is also less. The fact that NOx can be produced with as little as 300 degrees C is really neither here nor there the fact that the available oxygen is less is the big thing.

The reduction of combustion temps helps in other ways like reducing part throttle detonation. This was found when octane ratings were reduced while compression ratios were still a bit high.

Also your history of EGR is out by a few years. In the US EGRs, along with ULP, was being used by at least 1973.

don't forget about the N2, since exhaust gas also has some of the N bound up in NO2 thats reintroduced it would split and that O2 is freed up again to combine with hydro carbons to produce heat energy, CO2, H2O and free N2 with less free O2 that before. So there will be a equilibrium where the net NO2 is less in the exhaust stream. That is one path NO2 reduction would take as well as displacing fresh air already discussed.

I would be interested to put a vehicle on a gas analyser and compare EGR operating with it not operating to see not only NOx levels but O2 as well