Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
2000-09-29
2002-04-02
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06363726
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to gas turbine engine combustors, and more particularly to a combustor including a mixer having multiple injectors.
Fuel and air are mixed and burned in combustors of aircraft engines to heat flowpath gases. The combustors include an outer liner and an inner liner defining an annular combustion chamber in which the fuel and air are mixed and burned. A dome mounted at the upstream end of the combustion chamber includes mixers for mixing fuel and air. Ignitors mounted downstream from the mixers ignite the mixture so it burns in the combustion chamber.
Governmental agencies and industry organizations regulate the emission of nitrogen oxides (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO) from aircraft. These emissions are formed in the combustors and generally fall into two classes, those formed due to high flame temperatures and those formed due to low flame temperatures. In order to minimize emissions, the reactants must be well mixed so that burning will occur evenly throughout the mixture without hot spots which increase NOx emissions or cold spots which increase CO and HC emissions. Thus, there is a need in the industry for combustors having improved mixing and reduced emissions.
Some prior art combustors such as rich dome combustors
10
as shown in
FIG. 1
have mixers
12
which provide a rich fuel-to-air ratio adjacent an upstream end
14
of the combustor. Because additional air is added through dilution holes
16
in the combustor
10
, the fuel-to-air ratio is lean at a downstream end
18
of a combustor opposite the upstream end
14
. In order to improve engine efficiency and reduce fuel consumption, combustor designers have increased the operating pressure ratio of the gas turbine engines. However, as the operating pressure ratios increase, the combustor temperatures increase. Eventually the temperatures and pressures reach a threshold at which the fuel-air reaction occurs much faster than mixing. This results in local hot spots and increased NOx emissions.
Lean dome combustors
20
as shown in
FIG. 2
have the potential to prevent local hot spots. These combustors
20
have two rows of mixers
22
,
24
allowing the combustor to be tuned for operation at different conditions. The outer row of mixers
24
is designed to operate efficiently at idle conditions. At higher power settings such as takeoff and cruise, both rows of mixers
22
,
24
are used, although the majority of fuel and air are supplied to the inner row of mixers. The inner mixers
22
are designed to operate most efficiently with lower NOx emissions at high power settings. Although the inner and outer mixers
22
,
24
are optimally tuned, the regions between the mixers may have cold spots which produce increased HC and CO emissions.
SUMMARY OF THE INVENTION
Among the several features of the present invention may be noted the provision of a mixer assembly for use in a combustion chamber of a gas turbine engine. The assembly includes a pilot mixer and a main mixer. The pilot mixer includes an annular pilot housing having a hollow interior, a pilot fuel nozzle mounted in the housing and adapted for dispensing droplets of fuel to the hollow interior of the pilot housing, and one or more axial swirlers positioned upstream from the pilot fuel nozzle. Each of the pilot mixer swirlers has a plurality of vanes for swirling air traveling through the swirler to mix air and the droplets of fuel dispensed by the pilot fuel nozzle. The main mixer includes a main housing surrounding the pilot housing and defining an annular cavity, an annular fuel injector having a plurality of fuel injection ports arranged in a circular pattern surrounding the pilot housing and mounted inside the annular cavity of the main mixer for releasing droplets of fuel into swirling air downstream from the fuel injector, and one or more axial swirlers positioned upstream from the plurality of fuel injection ports. Each of the main mixer swirlers has a plurality of vanes for swirling air traveling through the swirler to mix air and the droplets of fuel dispensed by the fuel injection ports.
In another aspect, the mixer assembly of the present invention includes a main mixer having a plurality of swirlers positioned upstream from the plurality of fuel injection ports. Each of the main mixer swirlers has a plurality of vanes for swirling air traveling through the respective swirler to mix air and the droplets of fuel dispensed by the fuel injection ports.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.
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U.S. patent application Ser. No. 60/176,379, filed Jan. 14, 2000, entitled, “Method and Apparatus for Decreasing Combustor Emissions.”
U.S. patent application Ser. No. 09/054,794, filed Apr. 3, 1998, entitled, “Anti-Carboning Fuel-Air Mixer for a Gas Turbine Engine Combustor.”
Durbin Mark David
Held Timothy James
Mongia Hukam Chand
Andes William Scott
Freay Charles G.
Gartenberg Ehud
Hess Andrew C.
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