Question -
How is is it that employing EGR on a diesel increases peak combustion pressures (per the new Duramax press releases) when it is an established fact the EGR decreases peak combustion temperature - I thought they went hand-in-hand.
Just wondering.
Thanks in advance,
Jim
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The only thing I can think of is that it allows the fuel injection event to be timed differently so that the pressure peak is higher even though the temperature peak might be lower.
But you also have to remember that things like press releases are written by tech writers who get their information second hand from the real engineers, and sometimes they re-word it incorrectly.
The challenge with newer Diesel emissions standards is to control both NOx emissions as well as particulate emissions. EGR is an effective method to control NOx; Diesels can run more that 30% EGR. But, high EGR rates tend to lead to high particulate emissions. A way to minimize particulates is to run leaner. Uh oh, running leaner reduces engine output. To get the output back while staying leaner and running high EGR means one has to run significantly higher boost levels. And as we all know, higher boost will lead to higher peak cylinder pressures. QED.
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