[mwebb]

Originally Posted by serialk11r

Sorry, I probably should've said "pre-ignition temperature". EGR increases the mass of gas in the cylinder, which increases the pressure and temperature before ignition occurs. That's not saying that it helps combustion at all, or that it increases combustion temperature, etc. Well, the charge certainly starts at a higher temperature but since it's diluted it ends at a lower temperature most likely.

EGR when active does not change the mass of the contents of the combustion chamber .

EGR dilutes the air fuel mixture with an INert gas, exhaust , total mass of the gas in the combustion chamber is UN changed or very slightly DEcreased
Temperature and therefore pressure are DECREASED (in the combustion chamber) when EGR is active

because EGR dilutes / displaces some the air fuel mixture
EGR effectively
DECREASE the volume of the combustion chamber which also
DECREASES engine displacement at the time by the percentage of EGR gas in the combustion chamber

so
the use of EGR is one very simple easy and currently used method of
creating
a

Variable Displacement Engine , which just happens to be
the topic of this thread