Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-08-29
2001-08-14
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S746000, C060S742000, C060S748000, C239S404000, C239S405000
Reexamination Certificate
active
06272840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to fuel injection assemblies for gas turbine engines, and more particularly, but not by way of limitation, to fuel injectors of the general type known as lean direct injectors (LDI) which are designed to reduce nitrous oxide (NOx) emissions.
2. Description of the Prior Art
There is a continuing need, driven by environmental concerns and governmental regulations, for improving the efficiency of and decreasing the emissions from gas turbine engines of the type utilized to power jet aircraft or generate electricity. Particularly, there is a continuing drive to reduce nitrous oxide (NOx) emissions.
Advanced gas turbine combustors must meet these requirements for lower NOx emissions under conditions in which the control of NOx generation is very challenging. For example, the goal for the Advanced Subsonic Technology (AST) gas turbine combustor research being done by NASA is a 50 to 70 percent reduction in NOx emissions and an 8 percent improvement in fuel efficiency compared to ICAO 1996 STANDARDS TECHNOLOGY. Realization of the fuel efficiency objective will require an overall cycle pressure ratio as high as 60 to 1 and a peak cycle temperature of 3000° F. or greater. The severe combustor pressure and temperature conditions required for improved fuel efficiency make the NOx emissions goal much more difficult to achieve.
One approach to achieving low NOx emissions is via a class of fuel injectors known as lean direct injectors (LDI). Lean direct injection designs seek to rapidly mix the fuel and air to a lean stoichiometry after injection into the combustor. If the mixing occurs very rapidly, the opportunity for near stoichiometric burning is limited, resulting in low NOx production.
A general summary of the various types of fuel injectors for gas turbine engines is shown in the text of Lefebvre,
Gas Turbine Combustion
(1983) at Chapter 10 thereof. FIG. 10.61 of the Lefebvre text discloses the basic design features of a piloted airblast atomizer, having a central pilot simplex pressure atomizer surrounded by a main airblast atomizer.
U.S. Pat. No. 5,477,685 to Samuelson et al. discloses a lean burn injector utilizing a ring of radial injection ports, which inject fuel into a chamber where it mixes with swirling air.
U.S. Pat. No. 5,505,045 to Lee et al. discloses a dual airblast injector having first and second concentrically located airblast injectors.
U.S. Pat. No. 5,603,211 to Graves discloses an injector having an axial fuel injector surrounded by three swirlers having different swirl angles.
U.S. Pat. No. 5,816,050 to Sjunnesson et al. discloses a low emission combustion chamber for gas turbine engines having an axial pilot fuel injector having an associated first flow swirler, and having a main fuel injector which injects into an annular chamber divided from the pilot fuel injector by a divider wall.
Smith, et al., Journal of Propulsion and Power, Vol. 11, No. 2, March-April 1995, “Dual-Spray Airblast Fuel Nozzle for Advanced Small Gas Turbine Combustors”, p. 244-251, describes a dual airblast nozzle.
Thus, it is seen that there is a continuing need for improved designs in fuel injector systems, for gas turbine engines and particularly lean direct injector systems, for providing improved combustion efficiencies and reduced emissions of various pollutants, particularly NOx.
SUMMARY OF THE INVENTION
The present invention provides a fuel injection system for a gas turbine engine which includes a pilot fuel injector, a pilot swirler for swirling air past the pilot fuel injector, a main airblast fuel injector, inner and outer main swirlers for swirling air past the main airblast injector, and an air splitter located between the pilot swirler and the inner main swirler. For a dual airblast configuration, there is an additional air swirler radially inside the pilot fuel injector. The air splitter is so arranged and constructed as to divide a pilot air stream exiting the pilot swirler from a main air stream exiting the inner main swirler, whereby a bifurcated recirculation zone is created between the pilot air stream and the main air stream.
No central recirculation zone is created. The pilot fuel stream is either injected (at high fuel pressure drops) or centrifuged (at low fuel pressure drops) into the bifurcated recirculation zone. The pilot flame is aerodynamically anchored and separated from the main flame. This allows the pilot flame to operate in a stable manner on its own during low power operation, thus minimizing problems with lean blowout of the pilot.
A relatively large amount of air is introduced through the main swirlers. This air can effectively prevaporize and partially premix with the main fuel, resulting in a leaner and cooler high power flame which produces less NOx emissions.
Thus, a lean direct injection (LDI) fuel nozzle is provided which can achieve the desired low NOx emission goals while maintaining acceptable lean blowout performance. The radially staged injection of fuel and air between the pilot injector and the main injector is key to this performance. The radial staging accomplishes two important objectives. First, excellent fuel/air distribution resulting in very low NOx is achieved at high power conditions by injecting the fuel in the form of an inner pilot fuel injection and an outer concentric ring. Second, the radial staging of the two fuel injection streams provides good low power operability by allowing operation of only the inner stage at low power conditions such as engine idle conditions. The result is a relatively rich and stable pilot flame at idle conditions.
It is therefore, a general object of the present invention to provide an improved lean direct injector for gas turbine engines.
Another object of the invention is the provision of fuel injectors for gas turbine engines which result in low emissions of pollutants, particularly low NOx emissions, and CO emissions at low power conditions such as idle.
Another object of the present invention is the provision of a fuel injector for a gas turbine engine which has superior lean blowout performance.
Another object is that the fuel injector be designed to operate at the high power conditions of advanced gas turbine engines without thermal damage to the fuel injector itself
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3866413 (1975-02-01), Sturgess et al.
patent: 3937011 (1976-02-01), Caruel et al.
patent: 5224333 (1993-07-01), Bretz et al.
patent: 5256352 (1993-10-01), Snyder
patent: 5477685 (1995-12-01), Samuelson et al.
patent: 5505045 (1996-04-01), Lee et al.
patent: 5603211 (1997-02-01), Graves
patent: 5613363 (1997-03-01), Joshi et al.
patent: 5737921 (1998-04-01), Jones et al.
patent: 5816050 (1998-10-01), Sjunnesson et al.
patent: 5960724 (1999-10-01), Toqan et al.
patent: 5987889 (1999-11-01), Graves et al.
patent: 6189314 (2001-02-01), Yamamoto et al.
A general summary of the various types of fuel injectors for gas turbine engines is shown in the text of Lefebvre,Gas Turbine Combustion(1983) at Chapter 10 thereof.
Smith, et al., Journal of Propulsion and Power, vol. 11, No. 2, Mar-Apr 1995, “Duel-Spray Airblast Fuel Nozzle for Advanced Small Gas Turbine Combustors”, pp. 244-251.
AIAA Paper No. AIAA-87-1826, 1987,entitled “Design and Test Verification of a Combustion System for an Advanced Turbo Fan Engine” by Sanborn et al.
ASME Paper No. 2000-GT-117 entitled “A New Hybrid Airblast Nozzle for Advanced Gas Turbine Combustors”.
ASME Paper No. 2000-GT-0079 “Supression of Dynamic Combustion Instabilities by Passive and Active Means”.
Crocker David S.
Nickolaus Daniel A.
Smith Clifford E.
CFD Research Corporation
Kim Ted
Waddey & Patterson Lucian Wayne Beavers
LandOfFree
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