The smoke density decreases as the amount of biodiesel in the
blends increases as shown in Fig. 10. This is due to the cleaner
complete combustion happening in the engine. The unburned
hydrocarbon emissions of blended fuels are lesser than pure diesel.
This is shown in Fig. 11. This shows that use of biodiesel results in
more complete and cleaner combustion. The carbon monoxide
emissions decrease with increase in the amount of biodiesel. This
is shown in Fig. 12. This could be because biodiesel has low carbon
content and the more complete combustion results in CO2 rather
than CO. However, the biodiesel blends did not show significant
difference. Fig. 13 shows that CO2 emissions increase with increase
in biodiesel at higher loads. Some researchers (An et al., 2013) had
claimed that biodiesel emitted higher CO2 emissions because biodiesel
gave a more complete combustion and hence more CO
was transformed into CO2 [26]. But the opposite trend was also
reported by other researchers stating that biodiesel was a lower
carbon fuel compared to diesel due to the presence of oxygen atom
and biodiesel had a lower carbon to hydrogen ratio, so the total CO
emission was found to be lower with the use of biodiesel. The NO
emissions increase with increase in the biodiesel blend ratio as
shown in Fig. 14. This is due to the higher temperature of combustion
and also due to the higher amount of oxygen in the fuel. However,
some researchers (An et al., 2013) had reported reduced NOx
emissions or no regularity observed with the increase of biodiesel
blend ratio [26]. The exhaust gas temperature increases greatly
with the increase in biodiesel blend ratio due to the higher temperature
of combustion in the engine and is shown in Fig. 15.