Future Trends in Commercial Aviation Engines’ Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 111

Fig. 2 A typical rich-dome single annular combustor (SAC); adopted from Mongia ( 1997 )

±

corresponding nominal 10 %

Wa 3 variations between the different product engine designs (Mongia et al. 2004a , b ,
c , d , e , f ). Here Wa 3 is the total compressor discharge air

fl flow splits of 30, 40, and 30 %Wa 3 involving usually

flow rate, and part of this
bypasses the combustor (viz. 7 - 23 % Wa 3 ) as bleed, turbine cooling, and secondary
fl

fl

flows with attendant difference between the combustor discharge temperature T 4 and
the HP turbine rotor inlet temperature, T 41 . Therefore, air fl ow rate through the

combustor is given by Wa 3 : 1 ð 0 : 93 0 : 77 Þ Wa 3 . The combustor through fl flow air

Wa 3.1 is used for combustion to achieve essentially 100 % combustion ef ciency;

dilution and trimming for providing the required turbine inlet temperature quality
including pattern factor (PF) and radial pro le; and dome and liner cooling in order

to provide the combustor structure temperature levels and gradients consistent with
the material design capabilities and durability requirements.
The combustion air is usually divided into air injected through a discrete set of
primary/dilution jets, fuel nozzles, and dome-mounted swirlers which in many of the
modern rich-dome engines are combined into one functional hardware, namely fuel/
air mixing devices or simply called mixers, viz. swirl cup (Figs. 3 , 4 and 5 ) and high-
shear injector, Fig. 6 ; the former has been used by GE since the early 1970s and the
latter in the P&W TALON-X. The swirl cup along with the conventionally designed
primary zone (viz. the primary-zone air equivalence ratio

˕ closer to unity, providing

comfortable margins for ignition and flameout) followed by optimally spaced

dilution jets to allow soot burnout, and meet all the requirements of the

fl

rst gen-
eration of GE engines. However, in order to further reduce high-power NO x along
with idle CO and unburned hydrocarbons HC, a new set of design rules emerged for
the resulting GE low-emissions combustors LEC in the middle 1990s starting with