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      06-15-2014, 07:32 AM   #115
TDIwyse
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Drives: 2011 335d
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Quote:
Originally Posted by Jffeijao View Post
You are correct when you consider old technology EGR.
However with all actuators in the engine being controlled by software, EGR can improve the efficiency of combustion engines. Below is how:

1- Reduced throttling losses. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses. (Gasoline engines only as diesels are not throttled)

2- Reduced heat rejection. Lowered peak combustion temperatures not only reduces NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces;

3- Reduced chemical dissociation. The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC (Top Dead-Center), rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.

4- In a closed loop injection system, with EGR open, software is calibrated to inject less fuel in the cylinders

On diesel engines the improvement is smaller then on gas, but also occurs. .

I do not debate that blocking EGR reduces CBU. Therefore I do not judge as irrational your assessment on paying 10 bucks on a blocking plate instead of mantaining a clean intake via other measures. I just think the best economical decision would be buying a PFI gas car instead of a DI. Much cheaper engines and zero CBU!

If you have a solution for the emissions puzzle that eliminates EGR without negative collateral effects, start making money on it. All OEM's are desperate for a cheaper solution and removing parts will help
I'd be interested in reading the papers showing improvements in fuel consumption on a modern light duty common rail diesel engine when using EGR. The papers I've read show just the opposite. For example:

http://www.dieselnet.com/tech/engine_egr.php

The NOx emission benefit of EGR comes at a cost: other measures are usually required to avoid unacceptable increases in fuel consumption, emissions of PM, HC, and CO, engine wear and reductions in engine durability.

Then here is some direct measurements from my 335d operating in a back to back test with and without EGR. It shows quantifiable improvements to efficiency when not using EGR for highway operating conditions.

http://www.bimmerfest.com/forums/sho...0&postcount=60

Just a note on your point #1. Modern diesels do use throttle plates for controlling air flow in balancing the EGR. For example, here's a comparison of the EGR/Throttle behavior on my 335d.

http://www.bimmerfest.com/forums/sho...0&postcount=10

Also, the EGR recall that was performed was not, it seems, done to reduce CBU. Because it actually seemed to increase the use of EGR on my car. This is not helpful for reducing CBU. Here's data showing pre/post EGR recall behavior. Post recall the EGR was basically fully open most of the time... Yuck.

http://www.bimmerfest.com/forums/sho...3&postcount=67

And regarding the impact of NOx:

http://www.sciencedaily.com/releases...1030100022.htm

According to a new paper by Ott and Pickering in the Journal of Geophysical Research, each flash of lightning on average in the several mid-latitude and subtropical thunderstorms studied turned 7 kilograms (15.4 pounds) of nitrogen into chemically reactive NOx. "In other words, you could drive a new car across the United States more than 50 times and still produce less than half as much NOx as an average lightning flash," Ott estimated. The results were published July.
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