Environmental Engineering Reference
In-Depth Information
for determining the extent of distribution combustion conditions. Numerical simu-
lations have also been performed to help develop an understanding of the mixing
process for better understanding of ignition and combustion.
Keywords Distributed combustion
Ultra-low emission
High-intensity gas
turbine combustion
Colorless combustion
Green combustion turbine
Uniform
thermal
eld
1 Introduction
Increased concerns about pollutants emission and increased stringent regulations
concerning emissions from all kinds of propulsion and power systems have moti-
vated combustion engineers to develop novel combustion techniques for achieving
ultra-low levels of pollutants emission (such as NO x , CO, unburned hydrocarbons,
and soot) from gas turbine combustors and improve the pattern factor for increased
ef
field uniformity in
contemporary gas turbine combustors is far from adequate as the combustors do
suffer from local burnout, thus causing extensive system downtime as well as
increased emission of NO x, CO, unburned hydrocarbons, and soot. Colorless dis-
tributed combustion (CDC), which shares some similar principles utilized in high-
temperature air combustion (HiTAC) (Tsuji et al. 2003 ), has shown huge reduction
in emissions of NO x , CO, unburned hydrocarbons, and soot, along with improved
thermal
ciency and longer life of the turbine blades. The thermal
field uniformity in the entire combustor (improved pattern factor). Stable
combustion, alleviation of combustion instability, and low noise emission were also
demonstrated under CDC conditions for gas turbine combustion applications. The
fl
flames in distributed combustion do not show any visible
fl
flame signatures so that
the
fl
flame so formed is termed
colorless
due to negligible visible emissions from
the
ames.
Mixture preparation in gas turbine combustors can be by different means, and the
fl
flames as compared to conventional
fl
fl
flow mixture. Swirl provides
hot gas recirculation zone for better mixing of the reactants and increased residence
of the reactants in the toroidal recirculation zone of the combustor with the sub-
sequent result of compact
flame is stabilized using swirlers to radially stretch the
fl
flame stability limits over a wide
range of operating conditions (Gupta et al. 1984 ). A recirculation zone is created
downstream of the swirler, wherein the
fl
ame and enhanced
fl
flow reversal results in mixing of hot
product gases with the incoming fresh stream of reactants. This provides high and
uniform temperatures in the combustion zone in the form of a well-stirred reactor.
This hot mixture provides the ignition energy for the fuel to ignite and stabilize the
fl
fl
flame. In premixed condition, the reaction zone is stabilized in the region of
interaction between the product gases and the fresh stream and is often a very thin
reaction zone of the order of a millimeter. However, in non-premixed condition,
fuel is injected in the shear region formed near the zero streamline boundary and the
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