Performance of the combustor under normal temperature and
pressure was previously investigated [18]. These results are used
here for the baseline case for the purposes of comparison of the results
at other operational conditions examined here. Fig. 3 shows
the emission of NO and CO from the combustor under non-premixed
conditions. This exit arrangement (ATF1), demonstrated ultra
low NO emission with values of 6.4, 3.4, 1.5 PPM of NO for U
= 0.8, 0.7 and 0.6, respectively. Also this arrangement gave low
CO emissions, for instance, at U = 0.7, CO emission was found to
be 70 PPM. Such low CO emission, while having such a high heat
release intensity, can be explained by the higher residence time
available for the burned gases leading to higher CO conversion (increased
combustion efficiency), as the gases have to travel a longer
path before exiting from the combustor. These results provide a direct
role of better fuel-air preparation on NO and CO emission and
outline the importance of residence time for complete combustion
to occur in the combustor. In all cases the focus is not to allow themixture to ignite until the mixture is diluted and uniformly distributed
in the entire combustion chamber.
Fig. 4 shows the results obtained for NO and CO emissions
under premixed combustion condition. The results show even
low pollutant emissions for this combustor design. For example,
at U = 0.7, NO and CO were found to be 2 PPM and 50 PPM,
respectively.
The OH chemiluminescence intensity distribution images for
cases ATF1 and ATP showed increased reaction zone distribution
with the extended product gas exit tube inside the combustor
(see, Fig. 5). The resulting reaction zone formed a crescent opposite
to the fuel injection location. For premixed combustion, the reaction
zone is distributed along the combustor, with the highest
intensity located opposite to the injection location of air/fuel.
Images of OH chemiluminescence intensity show a decrease in
intensity with decrease in equivalence ratio for both the premixed
and non-premixed cases. This is to be expected as OH intensity increases
as one approached close to stoichiometric conditions.