water injection & detonation supression

[RABBITT_Andrew at mv8.orbeng.com.au]

>Gentlemen, OEMs use exhaust gas to supress detonation, right? Exhaust 
>gas recirculation systems to be exact, EGR.  This seams superior to 
>water injection. Is it?

EGR is primarily used for NOx control, although it is a variable that 
is sometimes manipulated for knock suppression.  It works by 
increasing the specific heat of the charge, hence reducing the overall 
combustion temperature.  Water injection works in the same way.  EGR 
enters the cylinder in the gas phase (as opposed to liquid), 
displacing air hence reducing the effective volumetric efficiency.
This is OK (beneficial actually) at part-load, but not WOT.