A comprehensive engine cycle simulation incorporating the
second law of thermodynamics was used to perform first and
second law analyses under different injection timings (6.5 and
1.5 aTDC) and EGR levels (0, 15, 30, 45%). Some conclusions can be
made here.
For both conventional (6.5 aTDC) and late injection (1.5
aTDC) timings, case A (0% EGR) shows the highest percentage
(w30%) of exergy destruction during the combustion process. As
the EGR level increases (together with the increase of inlet
temperature and equivalence ratio), the exergy destruction during
combustion decreases, mainly due to the intake charge heating
effect of the EGR and the corresponding increase in combustion
temperatures.
For both conventional and late injection timings, the percentage
of exergy transfer through flows increases as EGR increases, which
is attributed to the retarded ignition by increasing EGR. The
percentage of exergy transfer through heat exchange remains
almost unchanged.
For conventional injection timings, the combustion efficiency
remains constant as EGR level increases while the combustion
efficiency of late injection case decreases as EGR level increases.
The combination of late injection and very high EGR level is seen to
contribute to incomplete combustion.
Comparing to the conventional injection timing cases, the late
injection timing cases show lower percentage of heat transfer
exergy and higher percentage of net flow exergy. This could be
attributed to the longer ignition and the retarded combustion
phasing due to the late injection. This implies more exergy could be
utilized for the exhaust recovery process for the late injection cases