3.3. Low load operation
Fig. 9 shows the effect of EGR on contributions of the influencing factors to the improvement in the brake thermal efficiency at
the low load. With the similar analysis as in Section 3.2 by using
the values in Fig. 9, the sequence in importance of contributions
of the influencing factors to the improvement of fuel economy
when increasing EGR from 0% to 16% at the low load is: /w > gm > -
gth (the c effect) > gglh (adverse effect)> gb (adverse effect).The
reduction in the heat transfer loss /w due to lowered flame temperature plays dominant role in improvement of the brake thermal
efficiency with EGR, and the increased mechanical efficiency gm
owing mainly to the reduced pumping work during the gas
exchanging (or breathing) stroke is of the secondary importance .
Compared to the case at the medium load, another difference lies
in the degree of constant volume heat release gglh that has adverse
effect on the thermal efficiency. At the low load, as shown in