While the fraction of combustion irreversibility in the total
availability increases slightly with EGR at k = 0.9, it increases by
3.6% with EGR replacing the fuel enrichment. At k = 0.9,EGR reduces the flame propagation speed and lowers the combustion
temperature, thus increasing the combustion irreversibility. With
eliminati on of the fuel enrichment, the fraction of burned fuel increases, resulting in the increased fraction of combustion irreversibility. One may note that the fraction of indicated work in the total
availability is smaller than the fraction of brake work in the total
energy. This may be explained by the two facts:(1)as shown in
Fig. 5b the mechanical loss is very small,owing to the full open
throttle operation as well as the aggressive intake boosting;(2)
the total availability is larger than the total energy.Another note-
worthy is that both the fractions of heat transfer and exhaust gas in
the total availability are smaller than those in the total energy.
These results demonstrate the necessity of the second law analysis
when considering heat recovery as a strategy to maximize the
overall fuel conversion efficiency of internal combustion engines.