Mixture Preparation Effects on Distributed Combustion for Gas Turbine Application - Novel Combustion Concepts for Sustainable Energy Development - page 270

Mixture Preparation Effects
on Distributed Combustion for Gas
Turbine Application

Ahmed E.E. Khalil and Ashwani K. Gupta

Abstract Distributed Combustion is now known to provide signi cant improve-

ments to the performance of gas turbine combustors. Key features of distributed
combustion include uniform thermal

field in the entire combustion chamber for

signi cantly improved pattern factor and avoidance of hot-spot regions that promote

thermal NO x emissions, negligible emissions of hydrocarbons and soot, low noise,
and reduced air cooling requirements for turbine blades. Distributed combustion
necessitates controlled mixing between the injected air, fuel, and hot reactive gases
from within the combustor prior to mixture ignition. The mixing process impacts
spontaneous ignition of the mixture to result in improved distributed combustion
reactions. Distributed combustion can be achieved in premixed, partially premixed,
or non-premixed modes of combustor operation with suf cient entrainment of hot

and active species present in the combustion zone and their rapid turbulent mixing
with the reactants. Distributed combustion with swirl is investigated here to further
explore the bene cial aspects of such combustion under relevant gas turbine com-

bustion conditions. The near-term goal is to develop a high-intensity combustor with
ultra-low emissions of NO x and CO and a much improved pattern factor and
eventual goal of near-zero emission combustor. Different fuel injection scenarios are
examined with focus on mixing to achieve distributed reaction conditions and ultra-
low emissions. In all the cases, air was injected tangentially to impart swirl to the
fl

flow inside the combustor. Ultra-low NO x emissions were found for both the pre-
mixed and non-premixed combustion modes for the geometries investigated here.
Results showed very low levels of NO ( 21 PPM) emissions

under non-premixed mode of combustion with air preheats at an equivalence ratio of
0.6 and a moderate heat release intensity of 27 MW/m 3 -atm. Further enhancement of
the mixing process using dilution reduced NO emission to 4.6 PPM which is nearly
equivalent to emissions under premixed combustion mode with reduced CO emis-
sions compared to non-premixed combustion mode. Results are also reported on lean
stability limits and OH* chemiluminescence under different fuel injection scenarios

10 PPM) and CO (