5. Conclusions
Development of colorless distributed combustion (CDC) for gas
turbine applications requires careful examination on the role of
various operational conditions encountered, such as, preheated inlet
air temperature and elevated combustor pressure so as to simulate
the flow and other operations conditions of a gas turbine
combustor. Different operational conditions have been examined
here at thermal intensities varying between of 36 MW/m3-atm
and 22.5 MW/m3-atm for both premixed and non premixed combustion
regimes. Previous results obtained at normal temperature
and pressure has shown the ability of the current combustor design
to demonstrate very low pollutants emission. Emissions as
low as 3 PPM NO (non-premixed) and 2 PPM NO (premixed) have
been demonstrated.
The experimental results obtained from preheated inlet combustion
air showed a dramatic decrease in CO emission with increase
in air inlet temperature due to the added energy that
helps in the conversion of CO to CO2. The combustor was able to
sustain the flame at lower equivalence ratios with air preheats to
the combustor. However, increase in air inlet temperature led to
an increase in the combustor temperature which furnished the
combustor with more heat to form thermal NOx. This was mitigated
by running the combustor at lower equivalence ratios. Emissions
as low as 10 PPM NO and 21 PPM CO were demonstrated at
an equivalence ratio of 0.6 at a heat release intensity of 27 MW/
m3-atm for the non-premixed case. However, for premixed combustion,
lower emissions were shown (4 PPM NO and 11 PPM
CO). The same behavior was shown when the combustor was operated
at elevated pressure and normal temperature. The increased
pressure had an effect similar to that of increasing inlet air temperature,
wherein CO emissions decreased dramatically, operational
range increased and NO emissions increased. Emissions as low as
15 PPM NO and 8 PPM CO for non-premixed combustion at a heat
release intensity of 27 Mw/m3-atm were demonstrated. Premixed
combustion showed lower emissions of NO and CO as compared
to the non-premixed case.
The combustor exhibited similar behavior when the combustor
was operated with preheated inlet air to the combustor and elevated
combustor pressure. However, the combustor operating under
these conditions allowed one to obtain low NO emissions at
somewhat low equivalence ratios without experiencing incomplete
combustion or high CO emissions. The combustor produced
less than 10 PPM emissions (both NO and CO) at an equivalence ratio
of 0.5 and heat release intensity of 22.5 MW/m3-atm. For premixed
combustion, the combustor produced ultra low emissions
(5 PPM NO and 8 PPM CO) at a higher equivalence ratio of 0.6
and heat release intensity of 27 MW/m3-atm.
The experimental results obtained so far from the combustor
shows great promise to achieve near zero pollutant emissions at
gas turbine operational conditions where even higher pressuresare attributed, which will allow the combustor to sustain flame at
even lower equivalence ratios, where much lower NO (near zero)
emissions are produced without suffering from incomplete combustion
and high CO emissions. Our continued efforts will further
reduce the differences in pollutants emission between premixed
and non-premixed combustion cases by further efforts on modifying
our flowfield with the vision to achieve less (or same) emissions
from non-premixed combustion as compared to premixed
combustion. The global imaging showed no observable unsteadiness
in the flame under different operational conditions reported
here