In Fig. 2 it is given the comparison between calculated
and experimental cylinder pressure traces for 0%, 10% and
20% EGR at 1130 rpm engine speed, 100% load using an
injection timing of 91 ATDC. As observed there is a good
coincidence between calculated and measured values for all
EGR rates examined. The simulation manages to capture
the effect of EGR on the cylinder pressure trace, which
results to a small reduction of cylinder pressure during
compression and a more intense one during combustion
and expansion. This results from the increase of charge
specific heat capacity due to the presence of exhaust gas, to
the reduction of O2 availability that has a negative effect on
the combustion rate, and to the dissociation of CO2 and
H2O. It should be mentioned that for the cases examined
(full load) air-fuel ratio (AFR) values are close to their
lowest limit. Thus the presence of recirculated exhaust gas
in the engine intake reduces further oxygen availability,
which in the present case is a dominating factor in the
upcoming combustion event. Due to this, peak cylinder
pressure values are reduced, as the percentage of EGR
inside the engine cylinder increases.