Egr

[GlenB]

Can anyone explain the purpose of EGR?

[XtremeModifier]

It has several, the primary being to return incompletely-burned fuel to the intake so it can be burned more completely. Only runs during open loop too iirc (as in non WOT/closed loop).

[GlenB]

The Exhaust Gas Recirculation (EGR) system was created in the early 1970s for the same No. 1 ranking motivation that drives every other engine management system design — to reduce emissions. The EGR valve targets one specific pollutant, oxides of nitrogen (NOx).

Under normal combustion, the oxygen (O2) in the air plus hydrocarbons (HC) in the fuel combine into water (H2O); carbon dioxide (CO2) and the nitrogen remain unchanged. However, when things heat up in the combustion chambers to temperatures around 1,300° C or 2,500° F, all that changes. At those temperatures, oxygen and nitrogen start combining with each other and form NOx. This is a big problem because when the sunlight hits those NOx, they combine with hydrogen in the atmosphere. When that happens, we now have smog. So how do we combat that? By cooling the combustion chambers down to where normal combustion can take place.

There are several ways to lower the combustion chamber temps. Enrichening the fuel mixture, lowering the compression ratio, retarding the ignition timing, lowering the overall temperature of the engine, and reducing the amount of pure air can each lower the temperature in the cylinders. Problem is, all of those except for the last one will also reduce fuel economy. Also, each of those except for one will also raise the HC emissions. “Watering down” the intake air is the best choice. What is surprising though, is that this not only fixes a problem, it also brings efficiency improvements with it. It is a win/win situation.

EGR (Exhaust Gas Recirculation) cools the combustion event down by displacing some of the pure air that does support combustion, with exhaust gases that are inert and therefore do not support combustion.

How can EGR actually help fuel economy?

[XtremeModifier]

Yes, it does. Thus the reason diesel's are getting better and better fuel economy. Look up the BWA PTC website, it'll tell you alot about it.


More to add to your vast tech article on this topic - (since I found this online, I can talk about it in MINIMAL detail):

Additional combustion control, including an even more efficient variable-geometry turbocharging system, cooled (enhanced) Exhaust Gas Recirculation (EGR) and closed crankcase ventilation to reduce NOx
Additional exhaust control, including oxidizing catalyst and new Diesel Particulate Filter (DPF) to reduce soot and particulate matter
Increased-capacity cooling system
New engine control software
Use of low-ash engine oil
Actually, the cooler egr is quite something, since it will help keep your EGT's down. And any diesel owner will tell you (if they know anything about diesels) that EGT's will kill a diesel. I'm going to look up more on SAP once I get back to work, see if we have any detailed press releases on this yet.

Actually, I honestly can't wait to see the next-gen duramaxx's, powerstrokes, and cummins.