Fig. 4 shows CO emissions as a function of load for standard
diesel and the other four blends. It is clearly seen from the figure
that CO emissions increase by increasing ethanol and methanol
concentrations. This is perhaps due to lower cetane numbers of
alcohol fuels, which increase the ignition delay, leading to incomplete
combustion, which increases CO emission. Another observation
indicates that biodieseleethanolediesel blends result in higher
CO emissions than biodieselemethanolediesel. As compared to
diesel fuel, ethanol blended fuels produce higher CO emissions and
methanol blended fuels show lower CO emissions. However, it
is expected that if methanol concentration in biodiesele
methanolediesel is higher than 20%, biodieselemethanolediesel
blends might result in higher CO emission than diesel. This would
be because adding a small amount of methanol improves oxygen
content of blends, which leads to better combustion and lower CO.
But, as the methanol concentration increases, the cooling effects of
methanol reduce the gas temperature and leads to higher CO
emission. Thus, fuel blend ratio and operating conditions play
important roles in the change of CO emissions