The axial fuel staging (AFS) combustion is applied in
advanced
gas turbines as a result of its advantages in emission reduction and
operation flexibility at engine turndown conditions. In this study,
several chemical reactor network models for AFS combustors were established
to conduct simulation at the operating temperature of 1973 K. The
investigated parameters include the performance of fuel splits between
the primary stage and the secondary injectors, the equivalence ratios
of the injected mixture, and the residence time of vitiated products
in the secondary stage. The NO
x
reburning
mechanisms, which are proven to have a slight effect on total NO
x
emissions, were also considered in this
model. Simulation showed that the AFS combustor had considerable potential
in reducing NO
x
emissions as a result
of the primary stage temperature. Experiments were conducted to compare
the simulation results and further verify the advantages of the AFS
combustor. Given the mixing characteristics in a practical AFS combustor,
the performance of mixing characteristics, including the premixing
characteristics between the secondary injector air/fuel and the mixing
characteristic of jets in cross-flow on NO
x
and CO emissions, was investigated. Results show that the mixing
characteristics, especially the secondary injector mixing performance,
exert a substantial influence on NO
x
and
CO emissions. When the fuel split or the secondary equivalence ratio
increases, the NO
x
emissions decrease
first and then increase because the poor premixing of the secondary
flow exerts an influence. After optimization, the practical AFS combustors
demonstrate an improved NO
x
benefit when
the secondary stage is at the fuel-lean condition, and the “lean–lean”
mode shows a wider tolerance margin for the design of secondary injectors
than the “lean–rich” mode.