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vlt304 is close to the mark.
There are at least 3 maybe 4 different ways NOx is produced and along with these are different temps to produce it. It can be produced with as little as 300 degrees C. The EGR is used to lower the temp and also to displace "free" oxygen.

With regards to a car using more fuel because of the EGR, well ..... manufacturers tune engines with pollution equipment in place. They still tune cruise and low throttle openings at stoichiometric, fitting an EGR to an engine has practically no effect on fuel economy on its own. Why? well because we have O2 sensors and MAFs that determine how much fuel goes into the engine. More oxygen in the exhaust means more fuel is added, the EGR system displaces "free" oxygen and the outcome is less oxygen in the exhaust meaning less fuel is added to bring the engine back to stoichiometric conditions. If we are talking about carby engines that are tuned to gas analyser results then yes that statement would be correct but we aren't.

That is correct that EGR has little effect on AFR as its simply just displaces volume with inert gas. But the point 2 posts back is.... having more throttle and the EGR itself allowing a by pass of the throttle means less pumping losses thus improvement in economy.


Part of the reason diesel engine get such good economy as they have no throttle.

vlad01 wrote:But the point 2 posts back is.... having more throttle and the EGR itself allowing a by pass of the throttle means less pumping losses thus improvement in economy.

I didn't read it that way I read. This is what was written

Charlescrown wrote:They do not enhance fuel economy but increase it due to wider throttle opening required to maintain the same speed. Adding extra fuel under these driving conditions does nothing but cause a richer mixture due to the inert exhaust gas going in. It's up to 20% at it's maximum. Just ask Volkswagen how good they are. Modern engines use VVT to do the same job without clogging up the valve and passages with carbon deposits.

To me it reads the exact opposite of what you just said it reads.

Sorry I was replying to 2 people. You and Charlescrown

Maybe I confused my statement. Yes NOx is inert and all the EGR does is reduce the peak combustion temperature. If you put 600 deg gas into a combustion chamber which is reaching 1000 deg obviously the temperature will drop. I found a plate under an EGR valve with a manufacturers part number on it so I called a mate is spare parts and got him to run the number through the system only to find it didn't exist so manufacturers have been fiddling with the issues associated with EGR valves for a long time.

Ah, ok. I probably should have recognised that. Sorry if I appeared abrupt I'm not good at neutral tones online.

Rereading what you highlighted from Charlescrown has confused me now lol. The later part is exactly what I said but the sentence begins with disagreeing.

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

Charlescrown wrote:Maybe I confused my statement. Yes NOx is inert and all the EGR does is reduce the peak combustion temperature. If you put 600 deg gas into a combustion chamber which is reaching 1000 deg obviously the temperature will drop. I found a plate under an EGR valve with a manufacturers part number on it so I called a mate is spare parts and got him to run the number through the system only to find it didn't exist so manufacturers have been fiddling with the issues associated with EGR valves for a long time.

Some manufacturers, in my experience US GM is a shocker for it, can use more than 1 part number for an item but not stamp both on the item. 1 number is for ordering and the other is an internal number.

vlad01 wrote:Rereading what you highlighted from Charlescrown has confused me now lol. The later part is exactly what I said but the sentence begins with disagreeing.

It's been a long day