As emission standards become more stringent, many studies have
been carried out to understand and reduce the emissions from diesel
combustion engines, among which nitric oxide (NO) emissions and
soot are known to have the trade-off relation during combustion
processes. One aspect of this trade-off is manifested by the role
radiation heat transfer plays on post-flame gas temperature, thus
affecting NO formation. For example, a decrease in in-cylinder soot
decreases radiation heat transfer causing an increase in post-flame
gas temperature and partially contributing to the corresponding
soot-NO relationship with an increase in NO formation.
This topic has re-emerged with the increased use of biodiesel; a
potential explanation for the so-called "biodiesel
NOx penalty" is biodiesel's inherently reduced
in-cylinder soot. In order to assess how much radiation heat
transfer may affect NO formation, this study seeks to isolate and
control the soot formation of petroleum diesel through the use of
barium additive. To further assist the analysis of the experimental
results, a two-stage model that is capable of predicting
in-cylinder NO formation is used.
The experimental results show that soot concentrations decrease
with an increase in the barium additive. The expected result of a
corresponding increase in NO concentration with the soot
concentration, however, could not be statistically observed. The
behavior of the NO concentrations, for example, is better explained
by the changes in ambient temperature than by changes in soot
concentration.