the volume of gas in the combustion chamber does not increase with introduction of EGR
the total volume of gas remains the same only now
some of it is INert EGR gases that can not support combustion
the rest is the same mix of air fuel that was present without EGR
Wrong.
Test this with a vacuum gauge when you manually introduce EGR.
Vacuum drops, which means more mixture in cylinder at BDC on intake stroke, which means more compression at TDC on compression stroke. More in=less vacuum=more compressed=more compression.
Basic physics
The same applies for a vacuum leak introduced by disconnecting any hose from the manifold, except that allows more air into the cylinder instead of more exhaust.
regards
Mech
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