Low-Emission, Fuel-Flexible Combustion of Liquid Fuels - Novel Combustion Concepts for Sustainable Energy Development - page 469

Fig. 17 Effect of total heat
release on CO emissions for
50/50 mixture

for the same conditions as Fig. 16 .NO X emissions peaked to between 8 and 15 ppm
near the wall for all cases. Larger droplets migrating to the combustor periphery and
burning in diffusion mode are responsible for this result. The NO X concentrations
were within 5 ppm at the center of the combustor for all cases. The heat release rate
did not seem to affect the NO X emissions for the cases studied. Note that mea-
surements at the center represent values in a large combustor.

7.3 Effect of Fuel Composition

Figure 18 shows radial pro les of CO emissions for 50/50 and 75/25 glycerol

-
methane fuel compositions. The 0/100 and 25/75 cases were not of interest because
of their low glycerol content. Data were not taken for the 100/0 case because of the
unburned glycerol in the products. CO concentrations for the 50/50 case are around
3,000 ppm near the wall and 50 ppm at the center of the combustor. In comparison,
the 75/25 case results in CO concentrations of around 5,000 ppm near the wall and
300 ppm at the center of the combustor.
The lower methane content produces leaner mixtures with slower reaction rates,
and hence, poor thermal input to evaporate glycerol droplets, which leads to
incomplete combustion. Figure 19 shows the NO X emissions for the same condi-
tions as Fig. 18 . The NO X concentrations were generally higher for the 75/25 case.
The peak NO X emissions (near the wall) for the 75/25 case were around 20 ppm
while those for the 50/50 case were about 10 ppm. The smaller methane content for
the 75/25 case resulted in longer evaporation time for the glycerol spray, which led
to more droplets burning in diffusion mode to produce higher

fl ame temperatures or

thermal NO X .