Power plants – Combustion products used as motive fluid – Combustion products generator
Reexamination Certificate
1999-06-21
2001-09-18
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Combustion products generator
Reexamination Certificate
active
06289676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to gas turbine engines and, more particularly, to a fuel injector for such engines.
2. Description of the Prior Art
Many small gas turbine engines utilize fuel pressure to atomize fuel at the fuel nozzle of an injector to inject fuel into the combustion chamber. At low fuel flows, such as starting conditions, the fuel flow rate is too low to pressurize the fuel to produce adequate droplet size for a particular injector. Such fuel systems are designed for maximum pressure at full engine power. Thus, the smallest flow number possible for a given engine design is determined by the maximum pressure available from the fuel pump at maximum power. At starting conditions and low power, small quantities of fuel are required, thereby developing low pressure drop. This results in inadequate atomization at low power and leads to poor emissions and combustion instability.
Furthermore, since the fuel injector is immersed in a very hot environment of the gas turbine engine, stagnation of the fuel in the delivery passages can be detrimental to the injector in that the heat transfer from the walls of the injector is reduced which can lead to hot spots on the otherwise wetted wall. It has been found that excessive wall temperatures can lead to fuel coking and subsequent injector contamination. Low fuel flows in these regions further aggravate the situation.
In some cases, lack of adequate heat transfer in the stem may lead to unacceptable temperature gradients and attendant stresses in the stem which can affect its fatigue life.
It has been found that by swirling a substantial quantity of air around a nozzle of a fuel injector, an improvement in low power performance can be obtained. However, swirling the air can lead to flow separation around the face of the injector, resulting in carbon growth and overheating of the injector.
Air swirlers have been developed and are described in U.S. Pat. No. 5,579,645, Prociw et al, issued Dec. 3, 1996, and U.S. Pat. No. 6,082,113 for a Gas Turbine Injector by Prociw et al and assigned to Pratt & Whitney Canada Inc. The above-mentioned U.S. Pat. No. 5,579,645 and U.S. Pat. No. 6,082,113 is incorporated herein by reference. These air swirlers reduce flow separation at the injector. However, it is considered that other improvements are required to improve low power performance of the injector by improving fuel atomization at the injector.
The stem of the injector, that is, the elongated stem through which the various fuel conduits are contained, extends from the fuel source across the P
3
air envelope surrounding the combustor wall. The stem is also subjected to high temperatures and, therefore, problems of fuel stagnation that can lead to fuel coking is also possible within the stem.
SUMMARY OF THE INVENTION
It is an aim of the present invention to provide an improved injector wherein low power fuel atomization will be enhanced.
It is a further aim of the present invention to provide an injector that incorporates the advantages of the air swirler as described in U.S. Pat. No. 6,082,113 with an improved fuel injector.
It is a further aim of the present invention to provide an improved simplex pressure injector with improved low power performance.
It is yet a further aim of the present invention to provide an improved duplex pressure injector with improved low power performance.
It is an aim of the present invention to provide a fuel flow path within the stem and the injector tip which follows a circular path. Parts of the stem and the injector tip are provided with annuli which allow a circular and/or spiral path for the fuel.
It is yet a further aim of the present invention to provide an improved fuel flow passage in the stem of the injector. It is known that the velocity of the flow in the annular channels is controlled by appropriately sizing the inlet orifice to produce the correct pressure loss for the heat transfer rate required. According to the present invention, much higher velocities than would occur in conventional designs are attributable to the present method since a large portion of the fuel flow is in the tangential direction and not governed by the mass of fuel.
In the present invention, this control of the flow velocity to produce the correct pressure loss is determined not by a single metering or trim orifice at the inlet to the injector but by providing such metering orifices throughout the stem prior to the fuel entering the injector.
A construction in accordance with the present invention comprises a fuel injector for a combustor in a gas turbine engine, wherein the combustor includes a combustor wall defining a combustion chamber surrounded by pressurized air, the injector comprising an injector tip adapted to protrude, when in use, through the combustor wall into the chamber, the injector tip having an injector body extending along an injector tip axis, a primary fuel nozzle formed in the injector tip concentrically of the injector tip axis and communicating with a primary fuel chamber formed as a cone upstream of the fuel nozzle and coaxial therewith, at least a first annular fuel channel defined in the injector body upstream of the primary fuel chamber concentric with the injector tip axis and communicating with the primary fuel chamber, and means for providing a flow of pressurized fuel to the first annular channel tangentially thereof in order to provide a swirl to the fuel flow in the first annular fuel channel, the primary fuel chamber and thus to the injector tip, thereby atomizing the fuel as it exits the primary fuel nozzle.
More particularly, swirl slots communicate the first annular channel to the primary fuel chamber.
In a more specific embodiment of the present invention, there is provided a secondary fuel delivery arrangement whereby a secondary annular fuel channel is provided concentrically and outwardly of the primary fuel channel, a secondary annular conical fuel swirl chamber is provided concentrically and outwardly of the primary swirl fuel chamber, and a secondary fuel nozzle is provided concentrically and outwardly of the primary fuel nozzle and the injector tip axis, means for providing a flow of pressurized fuel to the secondary annular channel tangential thereof in order to provide a swirl to the fuel flow in the secondary annular fuel channel, the secondary annular fuel channel communicating with the secondary fuel swirl chamber so as to provide a swirl to the fuel whereby the secondary fuel will exit the secondary fuel nozzle in an atomized fashion.
It has been found that when the tangential velocity of the swirling fuel increases as it progresses in the conical primary fuel chamber, external air is entrained back into the primary fuel chamber along the tip axis, resulting in the formation of a thin hollow spinning film of fuel in the primary fuel chamber. As the fuel exits from the nozzle, it forms a thin conical unstable film that breaks down into droplets.
It is a further feature of the present invention to provide the injector with an air swirl member defining first air passages forming an annular array communicating the pressurized air from outside the wall into the combustion chamber, the first air passage being concentric with the primary fuel nozzle and the tip axis whereby the first air passages are arranged to further atomize the fuel emanating from the primary fuel nozzle, and a set of second air passages arranged in annular array in the injector tip spaced radially outwardly from the first air passages whereby the second passages are arranged to shape the spray of the mixture of atomized fuel and air and to add supplemental air to the mixture.
In a further embodiment of an injector in accordance with the present invention including an injector tip that has annular fuel flow passages, there is a stem containing at least one fuel flow passage extending from a stem fuel inlet to a fuel delivery outlet, a first annular fuel flow cavity provided in the stem near the fuel stem inlet, an inlet conduit extending from the f
Prociw Lev Alexander
Sampath Parthasarathy
Shafique Harris
Astle Jeffrey W.
Pratt & Whitney Canada Corp.
Rodriquez William H
Thorpe Timothy S.
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