A very slight amount of EGR at light cruise, will simulate a smaller displacement engine, because of the inert gas taking up space in the cylinder, any mileage increase would be hard to chart because the lowering of the cylinder temp by EGR also takes away from the engines thermal efficiency.
Just out of curiosity:
- why does a slight amount of exhaust gas (instead of the same amount of fresh air) simulate a smaller displacement engine? Aside from the lower oxygen content in the cylinder with recirculated exhaust gas.
- why would inert gas increase the gas mileage. Unless the ECU knows (which it might, assuming MAF sensor signal and EGR signal allow an accurate enough oxygen balance calculation) that less oxygen is available and reduces the amount of injected fuel (and power, so not comparing apples with apples) for a fuel savings at reduced power
In this context a really diesel newbie question:
Is the diesel ECU determining (from driver input) the amount of fuel needed, and then calls up (turbo) the required air?
Or the other way around, determines the air requirement (boost, MAF) and then injects the fuel (like on gas engine)?