EGR gas temperature soot oxidation ceases earlier during
the expansion stroke due to lack of O2. This provides an
explanation for the negative effect of EGR gas temperature
increase on soot emissions. The small variation of NO with
EGR temperature is explained observing the variation of
local zone gas temperature and considering Fig. 5
providing the effect of EGR temperature on the overall
AFR. The small increase of local gas temperature with
increasing EGR temperature has a small positive impact on
NO formation, which is obviously overwhelmed by the
decrease of O2 percentage. The last two mechanisms result
to a very small increase of NO within the EGR temperature
levels examined, which is more pronounced at high EGR
rates.