Abstract:
A fuel injector for a combustor presented either as a simplex or duplex pressurized fuel injector, wherein the fuel is introduced into the injector to provide a swirl to the fuel in a first annular channel which communicates with a coaxial conical fuel swirl chamber and then the primary nozzle. In a duplex version, a secondary annular swirl channel is provided for spinning the fuel and communicating downstream with a conical fuel swirl chamber and eventually an annular nozzle whereby the fuel is atomized as it exits the nozzle. An air swirler is also provided with the fuel injector, and the air swirler includes air passages arranged in an annular array about the fuel injector tip. A second array of auxiliary air passages can be arranged spaced radially from the first array and also to provide an air swirl and to control the spray cone of the fuel air mixture.

Description:
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 &amp; 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 fuel stem inlet to the annular cavity, the inlet conduit being angled to provide a tangential flow direction to the fuel passing through the conduit to the annular cavity, an outlet conduit extending at an acute angle from the first annular cavity to receive the fuel therefrom in a tangential direction, a first linear fuel conduit extending from the outlet conduit and extending axially of the stem and communicating with an injector inlet conduit at the fuel delivery outlet, the injector inlet conduit being angled to direct the fuel flow to a first annular passage in the injector tip in a tangential direction to provide a swirl to the fuel flow entering the annular passage in the injector tip. 
     In a more specific embodiment of the present invention, there is provided a metering of the fuel flow in the various conduits in the stem where alternating fuel flow conduits have differing cross-sectional areas arranged to provide the proper velocity to the fuel flow and result in the pressure loss to enhance the heat transfer rate. 
     As can be seen, throughout the injector tip and the stem, care has been taken to ensure tangential injection into the annular passages, thus maximizing the angular momentum of the fuel flow into the annular channels. The kinetic energy in the flow is dissipated at the stem and injector walls enhancing the heat transfer of the passages. 
     The passage metering and the fuel swirl slots in the injector tip are designed to control injector temperature and to eliminate fuel stagnation wherever possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration, a preferred embodiment thereof, and in which: 
     FIG. 1 is a fragmentary vertical cross-section of an injector in accordance with an embodiment of the present invention; 
     FIG. 2 is a front elevation of the injector in accordance with FIG. 1; 
     FIG. 3 is a fragmentary axial cross-section in accordance with another embodiment of the injector in accordance with the present invention; 
     FIG. 4 is a perspective schematic view showing the flow passages of the injector in accordance with the present invention, including both the injector tip and the stem; 
     FIG. 5 is a schematic view showing the fuel passages within the injector tip of the embodiment shown somewhat in FIG. 1; and 
     FIG. 6 is a perspective schematic view showing the flow passages based on the embodiment shown in FIG. 3 of the injector tip but showing only the secondary fuel flow passages. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present specification describes two embodiments of the present invention. The first embodiment shown in FIGS. 1 and 2 is a simplex injector while the second embodiment shown in FIG. 3 is a duplex injector. 
     Referring to the embodiment shown in FIGS. 1 and 2, the simplex injector is designated by the reference numeral  30 . The injector  30  is shown mounted in an opening in the combustor wall  31 . The injector  30  includes an injector body  32 , an injector face  33 , as shown in FIG. 2, and an injector tip  34 . 
     A tip axis X extends through the tip  34  and the body  32 , as shown in FIG. 1. A stem  40  is connected to the body  32 , and at least a fuel passage  36  is formed in the stem  40  which is also covered by protective sleeve  38 . The body  32  defines cavities, such as annular channels  41 ,  42 , and  44 , that are concentric to the tip axis X. The fuel line  36  communicates with the channel  41  in a somewhat tangential manner in order that the fuel under pressure will be provided a swirl in the annular channel  41 . The annular channels  42  and  44  communicate with each other by means of slots  46  which are defined helically so as to provide a swirl or spin to the fuel as it passes from the annular channel  42  and to channel  44 . 
     A conical fuel swirl chamber  48  is defined downstream of the channel  44 , and slots  49  communicate the channel  44  to the chamber  48 . As the diameter in the conical chamber  48  decreases, the velocity of the spinning fuel increases until it reaches the cylindrical nozzle  50 . It is believed that the spinning fuel flow will create a film on the conical walls of the chamber  48  by centrifugal force, and external air may be drawn into the chamber to flow back along the tip axis X into the chamber  48 . This separation effect results in a thin, hollow, spinning film which develops at the nozzle  50 . As the fuel leaves the nozzle, it forms a thin conical sheet which stabilizes into droplets. 
     An annular air swirl member  52  is connected to the injector tip  34 , as shown in FIGS. 1 and 2. The air swirl member  52  comprises a series of annular spaced-apart passages  54  distributed around the nozzle  50 . As described in U.S. Pat. No. 6,082,113, the air flow from P 3  air into the combustor passes through the holes or passages  54  in such a way as to avoid flow separation and to develop a conical fuel spray pattern within the combustor. 
     A second set of annularly spaced-apart passages  56  may be provided to shape the fuel air cone and to augment the combustion air into the combustor. Both sets of passages  54  and  56  are specifically sized to admit a predetermined quantity of air at the engine design point. 
     Referring now to the embodiment of FIG. 3, the duplex injector  60  is described which includes an injector body  62  and an injector tip  64 . The tip axis X 2  passes through the injector tip  64  as shown. 
     The injector body  62  fits in a stem cavity  74 . In this embodiment, the air swirl member  66  includes a cylindrical portion which has a greater diameter than the injector body  62 . 
     The injector body  62  defines, with the cavity  74  of the stem  72 , a primary fuel channel  68 . The fuel channel  68  is annular because of the valve device  73  within the cavity so formed. The fuel annular channel  68  communicates with the primary fuel line  86  which is arranged to deliver the pressurized fuel tangentially of the channel  68  so as to create a fuel swirl within the primary fuel channel  68 . 
     A primary fuel swirl chamber  70  is defined as a conical chamber downstream of the channel  68  and communicates with the nozzle  71 . Slots  75  are defined between the valve  73  and the conical wall of the chamber  70 . These slots are designed to enhance the spinning effect of the primary fuel from the primary fuel channel to the primary fuel chamber  70  and ultimately through the nozzle  71 . 
     A secondary fuel channel  76  is formed between the injector body  62  and the cylindrical portion  67  of the air swirl member  66 . Passages are provided in the cylindrical member  67  to communicate with the secondary fuel line  88  in the stem  72 . The fuel line and the passages will provide a swirl to the secondary fuel as it enters the secondary annular channels  76 . The annular channel  76  communicates with the downstream annular secondary fuel channel  78  by means of slots  80  which are designed to enhance the swirl of the secondary fuel. A conical secondary fuel chamber  82  is also provided which is annular to the axis X 2  and the primary fuel chamber  70 . The secondary fuel chamber  82  has the same effect on the secondary swirling fuel as has the primary chamber  70 . An annular nozzle  84  is also provided in order to allow the secondary fuel to form a conical spray with the primary fuel in the combustion chamber defined by combustor wall  94 . 
     The air swirl member  66  is provided with air swirl passages  90  so as to focus the air flow from the P 3  air into the combustion chamber just outside the fuel injector face. Auxiliary air passages  92  are also provided in the swirl component  66  and have a similar effect to those described with the simplex injector  30 . 
     It is noted that another difference between the duplex injector  60  and the prior art is the absence of core air passages and the primary injector heat shield. The elimination of these elements reduces the manufacturing complexity as well as its cost. A duplex injector  60  is more compact for a given fuel flow rate. This injector does not have to be concerned with the heat transfer problems arising from the presence of core air in the interior passage of the injector. The integration of the air swirler component  66  with the fuel nozzles  71  and  84  helps reduce the overall size of the injector tip  64 . The swirl component  66  design with the duplex injector  60  aids atomization particularly at low power when the fuel pressure in the secondary annular channel is too low to generate the thin film required for adequate atomization. 
     Referring now to FIG. 4, the stem  172  is shown generally in dotted lines. However, primary passage  174  and secondary passage  176  are illustrated in this drawing. The injector  160  is a duplex injector similar to that described in relation to FIG.  3 . Thus, the injector tip  160  includes a primary fuel channel  168  and a secondary fuel channel  175 . 
     The remote end of the stem is provided with a primary fuel inlet  140  which communicates with a circular cylindrical primary fuel chamber  142  by means of the inlet conduit  144 . As noted in the drawings, the conduit  144  is angled so that it delivers the fuel in a tangential direction within the cylindrical primary fuel chamber  142 . The primary fuel chamber  142  is shaped to allow the primary fuel to flow to swirl therein and exit through an outlet conduit  146  which is of somewhat smaller diameter than the chamber in order to provide a first metering passage. The conduit  146  communicates with a linear conduit  148  which has a larger cross-sectional area than the conduit  146 . 
     The linear conduit  148  communicates with a delivery conduit  186  which is angled to deliver the primary fuel into the annular channel  168  tangentially. The delivery conduit  186  is also of a smaller cross-sectional area than the conduit  148  in order to meter the fuel flow into the channel  168 . 
     The secondary fuel passage  175  of the stem  172  has a secondary fuel inlet conduit  150  which is angled to deliver the fuel to the annular channel  152  at the entry end of the stem  172 . An outlet conduit  154  delivers the fuel flow from the annular channel  152  at a somewhat tangential angle to deliver the fuel to the linear conduit  156  which is of a larger cross-sectional area than the conduit  154 . At the injector end of the stem, an angled two-part delivery conduit  188  is provided for delivering the fuel to the annular channel  175  in a tangential direction so as to provide a swirl to the fuel flow within the annular channel  175 . 
     FIGS. 5 and 6 correspond generally with the injector tip of FIG. 1, and although there are some constructional differences, they do resemble each other in principle. 
     Thus, the reference numerals used in FIG. 5 will correspond to the reference numerals used in FIG. 1 but have been raised by 200. 
     Thus, the fuel is delivered by means of the delivery conduit  236  into the annular channel  241 . The slots  246  are all angled to deliver the fuel from the channels  241  and  242  into the annular channel  244 . Angled slots  249  deliver the fuel tangentially to the chamber  248 . 
     The schematic depiction of the fuel flow passages shown in FIG. 6 resembles the duplex injector shown in FIG.  3 . The drawing represents the secondary fuel distribution in the injector tip (the primary flow is not shown) and that will now be described with similar reference numerals to those used in FIG. 3 but raised by 300. 
     Thus, the delivery conduit  388  is shown here with its two components  388   a  and  388   b . As noted, the cross-sectional diameter of the conduit portion  388   a  is larger than the cross-sectional diameter of the portion  388   b , thereby providing the metering effect mentioned previously in order to provide the proper pressure drop. 
     The delivery conduits  388   a  and  388   b  are so arranged in the stem that the portion  388   b  is directed tangentially to the annular channel  375  or  376 . The so-called angular slots  380  are, in fact, as shown in FIG. 6, in two parts, one being a first outlet portion  380   a  delivering the fuel from the channel  376 , and the second part  380   b  is of a smaller diameter and is angled to provide the fuel flow tangentially to the conical fuel swirl chamber  382 .