Combustor with fuel preparation chambers

Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature

Reexamination Certificate

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Details

C060S737000

Reexamination Certificate

active

06286300

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to combustors used in gas turbine engine and in particular to a fuel preparation chamber which uniformly mixes fuel and air so as to reduce NOx formed by the ignition of the fuel/air mixture.
BACKGROUND OF THE INVENTION
Air pollution concerns worldwide have led to stricter emissions standards requiring significant reductions in gas turbine pollutant emissions for both industrial and power generation applications and propulsion applications. Nitrous Oxide (NOx), which is a precursor to atmospheric pollution, is generally formed in the high temperature regions of the gas turbine combustor by direct oxidation of atmospheric nitrogen with oxygen. Reductions in gas turbine emissions of NOx have been obtained by the reduction of flame temperatures in the combustor by a variety of techniques including “rich burn, quick quench, lean burn” and “lean premix” combustion.
Many propulsion engines employ annular combustors to burn fuel. The fuel is metered and sprayed into the combustor through a plurality of fuel nozzles along with combustion air having a designated amount of swirl. The prior art, however, does not disclose a nozzle or the dome end of the combustor configured to mix the fuel and air uniformly to reduce the flame temperatures. Accordingly, non-uniformity of the air/fuel mixture causes the flame to be locally hotter; leading to significantly enhanced production of NOx.
In the typical aircraft gas turbine engine, flame stability and variable cycle operation of the engine dominate combustor design requirements. This has in general resulted in combustor designs with the combustion at the dome end of the combustor proceeding at the highest possible temperatures at stoichiometeric conditions, which in turn, leads to large quantities of NOx.
While premixing ducts in the prior art have been utilized in lean burning designs, they have been found to be unsatisfactory due to flashback and auto-ignition considerations for modern propulsion applications. Flashback involves the flame of the combustor being drawn back into the mixing section, which is most often caused by a backflow from the combustor due to compressor instability and transient flows. Auto-ignition of the fuel/air mixture can occur within the premixing duct if the velocity of the airflow is not fast enough, i.e., where there is a local region of high residence time. Flashback and auto-ignition have become serious considerations in the design of mixers for propulsion engines due to increased pressure ratios and operating temperatures.
Accordingly, there is a need for a fuel preparation chamber that provides a more uniform mixture of fuel and air in the combustor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide for a low emissions combustor for use in gas turbine engines.
Another object of the present invention is to provide a method for forming a low emissions gas in a combust.
The present invention achieves this object by providing an annular combustor having fuel preparation chambers mounted in the dome of the combustor. The fuel preparation chamber comprises a cylindrical wall extending axially from an inlet to an exit that defines a mixing chamber. Mounted to the inlet are an air swirler and a fuel atomizer. The air swirler provides swirled air to the mixing chamber while the atomizer provides a fuel spray. On the downstream side of the exit, the fuel preparation chamber has an inwardly extending conical wall that compresses the swirling mixture of fuel and air exiting the mixing chamber.
A method for producing a low emission gas in a combustor is also disclosed. The method includes injecting a fuel spray into a plurality of circumferentially disposed premix chambers, each of which fluidly communicates with a single combustion chamber. Concurrently and concentrically with the fuel spray swirled air is flowed into each of the premix chambers to form a swirling mixture of fuel and air. The swirling mixture is than compressed before entering the combustion chamber. Upon entering the combustion chamber, the swirling mixture is expanded and ignited to form a low emissions gas.


REFERENCES:
patent: 2729062 (1956-01-01), Hennig
patent: 3589127 (1971-06-01), Kenworthy
patent: 3886728 (1975-06-01), Quinn
patent: 3905192 (1975-09-01), Pierce et al.
patent: 4054028 (1977-10-01), Kawaguchi
patent: 4187674 (1980-02-01), Richardson
patent: 4373342 (1983-02-01), Willis et al.
patent: 5251447 (1993-10-01), Joshi et al.
patent: 5450725 (1995-09-01), Takahara et al.
patent: 5638682 (1997-06-01), Joshi et al.

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