[mwebb]

..."EGR is for reducing the combustion temperature
(less O2=less NoX produced) and it has the side advantage of reducing power losses from the engine having to work to make a vacuum in the intake. All of this has been trumped by variable valve timing, which adjusts the effective compression ratio per the currents needs of the engine by adjusting the timing and duration of the valves opening and closing. "...

EGR does reduce combustion temperature
because
the INert gases take up space in the combustion chamber and act like a cushion
reducing
COMBUSTION PRESSURE which ultimately is what actually reduces
COMBUSTION TEMPERATURE and since NOX does not form below a certain temperature
the formation of NOX is reduced by reduction in combustion temperature which was reduced by reduction in
COMBUSTION PRESSURE which was reduced by the addition of an INert gas to the combustion event
by
Exhaust gas recirculation , EGR .

variable cam timing changes Exhaust ValveOpen and Exhaust Valve Close and Intake Valve Oepn and Intake Valve Close
timing relative to the Crankshaft position
so that the exhaust valve closes before all of the exhaust can escape the combustion chamber from the previous combustion event
thus
trapping some INert exhaust gases in the combustion chamber for the next combustion event
one drawback of this method is that the exhaust gases trapped are much hotter than EGR routed from an EGR valve through external plumbing .

EGR percentage can be very high depending on the application and the engine size measured by displacement
is reduced by the percentage of EGR gases introduced at the time .
a 2 liter engine becomes a 1.5 liter engine with 25% EGR

VW diesels use up to 45% a toyota prius uses up to 30% egr .

smaller displacement engines use less fuel than bigger displacement engines

KISS version s

carry on