Yes, EGR systems introduce a certain quantity of inert gases in combustion chamber, lowering combustion temperatures and so reducing NOx formation. This effect is comparable to that of water injection, or to the use of a fuel/water emulsion, such as the so called (in Europe) "white Diesel...
Jon
The relationship between inlet (T1) and outlet (T2) temperature is linear:
T2=T1*beta^((k-1)/k)
where beta=p1/p2 is the pressure ratio and k is the politropic coefficient (reasonably constant if the two temperatures are not too different).
For example, if you reduce the inlet temp from...
It depends from the arrangement of the exchanger and flow rates. There are some experimental relations between efficiency and NTU (Number of Transfer Units), for several geometries.
Roughly, for a single pass cross-flow heat exchanger you can assume 0.75/0.85.
