Quote Originally Posted by SubGothius View Post
That's a common misconception; the actual purpose and function of any EGR valve is to lower combustion temperatures by diluting the intake charge with inert (already-combusted) gases without affecting the fuel-oxygen ratio, thereby reducing NOx emissions formed at high combustion temps, which in turn lead to smog.
It can't hurt to also note that the desired effect of the addition of the inert gases is to ensure that ignition occurs at the proper time, thereby reducing the high temps that allow oxides of nitrogen (NOx) to form. The lower temp also prevents detonation and allows for more advanced timing.