3.2. Medium load operation
Fig. 6 shows the effect of EGR on contributions of the influencing factors to the improvement in the brake thermal efficiency at
the medium load. With increasing the EGR from 0% to 17%, gth increases
by 0.5%, gb decreases by 1.9%, /w decreases by 3.8%, gglh increases
by 1.5%,and gm almost does not change.Therefore, the
sequence in importance of contributions of the influencing factors
to the improvement of fuel economy by using EGR at the medium
load is: /w > gglh > gth (the c effect) > gm > gb (adverse effect).
Fig. 7 shows the cumulative heat release normalized by its maximum value and the rate of heat release.With increasing EGR,the
combustion phasing CA50 (the crank angle at 50% of the normalized cumulative heat release) is advanced; meanwhile the rate of
heat release becomes slower. The advanced CA50 leads to the increased gglh, while the slower rate of heat release decreases it. As
a balanced result, with increasing EGR from 0% to 17% gglh is increased by up to 1.3%, as can be calculated from the data in