Quote:
Originally Posted by mwebb
EGR when active does not change the mass of the contents of the combustion chamber .
EGR dilutes the air fuel mixture with an INert gas, exhaust , total mass of the gas in the combustion chamber is UN changed or very slightly DEcreased
Temperature and therefore pressure are DECREASED (in the combustion chamber) when EGR is active
because EGR dilutes / displaces some the air fuel mixture
EGR effectively
DECREASE the volume of the combustion chamber which also
DECREASES engine displacement at the time by the percentage of EGR gas in the combustion chamber
so
the use of EGR is one very simple easy and currently used method of
creating
a
Variable Displacement Engine , which just happens to be
the topic of this thread
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You have to consider at what time in the cycle. Before ignition, the pressure and temperature are higher because a greater mass (or number of particles or whatever you want) of gases (at approximately the same temperature) has been compressed to the same volume. After ignition, the same amount of heat energy from the fuel is going into a greater mass of gas, so the temperature is lower.