Abstract:
A fuel system having an ecology valve controlling liquid flow through a retention passage when pressurized liquid is passed through the valve is presented. The retention passage winds between the valve outlet and a cavity such that no matter which way the valve is oriented gravity alone is unable to drain liquid from the cavity to the outlet. The ecology valve serves to suction fuel from fuel nozzle passages upon engine shutdown. Fuel is temporarily stored in the cavity and the retention passage. The ecology valve also provides a fuel splitting function for providing a port geometry determined split between fuel nozzles in the fuel system.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to fuel delivery systems for engines and more particularly to ecology and fuel flow splitting functions for such fuel delivery systems. 
   BACKGROUND OF THE INVENTION 
   In many gas turbine engines, the fuel system for regulating the flow of fuel to the combustion chamber consists of one or more fuel nozzles arranged in the combustion chamber, a fuel pump for pressurizing fuel from the fuel supply, a fuel metering unit for controlling the flow of fuel to the fuel nozzles and one or more fuel manifolds fluidically connecting the fuel metering unit to the fuel nozzles. 
   During engine start-up, fuel is pumped from the fuel supply to the fuel metering unit by the fuel pump and, once a sufficient start-up pressure is attained, the pressurizing valve of the fuel metering unit opens and fuel is supplied to the fuel nozzles via the fuel manifold. Thereafter, the metering valve of the fuel metering unit modulates the rate of fuel flow from the fuel supply to the nozzles. As such, a single, continuous flow path exists from the fuel metering unit, through the fuel manifold, to the fuel nozzles. 
   In more advanced gas turbine aircraft engines, however, the fuel system includes additional components and has multiple flow paths. For example, a dual flow path fuel system may include multiple sets of fuel nozzles (i.e., a primary fuel nozzle and a secondary fuel nozzle), two fuel manifolds (i.e., a primary manifold and a secondary manifold), and a flow divider valve arranged downstream of the fuel metering unit. In such systems, the flow divider valve splits the flow of fuel from the fuel metering unit into two distinct flow paths, namely a primary flow path and a secondary flow path. 
   In dual flow path fuel systems, fuel is delivered to the primary and secondary nozzles in a predetermined and scheduled manner. For instance, during engine start-up, fuel is initially supplied only to the primary fuel nozzles. However, once the fuel from the primary fuel nozzles is burning in a steady and satisfactory manner, fuel is thereafter supplied to the secondary nozzles. Put another way, the primary flow path provides a pilot flow, or a flow which initiates the combustion process, while the secondary flow path provides a main flow, or a flow which supplements and intensifies the combustion process once the pilot flow is burning steadily. 
   Fuel systems for some gas turbine engines require an ecology function that removes a set amount of fuel from the fuel nozzles and manifolds upon cessation of engine operation. The removal of fuel serves two purposes. It prevents the fuel from trickling into the still hot combustion chamber, which causes the fuel nozzles in the engine to coke and/or the engine to smoke. This hinders engine performance and leads to premature failure of the nozzle. The removal of fuel also keeps the fuel from vaporizing into the atmosphere, which is not acceptable from an environmental standpoint. 
   Prior fuel systems such as disclosed in U.S. Pat. No. 5,809,771 to Wernberg use one ecology valve and one flow divider valve for all the nozzles when the fuel manifolds are small in diameter and there are relatively few nozzles. However, using one flow divider valve to split flow between multiple nozzle assemblies results in the addition of a second flow manifold. For small engines this is only a small weight and cost penalty. Larger engines utilizing many nozzle assemblies require proportionately larger and heavier ecology and flow divider valves as well as an additional large and heavy fuel manifold. To avoid this additional manifold some larger engines have small flow divider valves at each nozzle assembly. However, these flow divider valves do not provide the ecology function. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention provides an ecology valve in a fuel system that also serves to divide fuel flow between nozzles. The ecology valve controls liquid flow through retention passages when pressurized liquid is passed through the valve such that no matter which way the valve is oriented gravity alone is unable to drain liquid from the valve inlet to the outlet. The retention passages includes grooves formed into either the valve body or in a sleeve that is inserted into the structure enclosing the retention passages. 
   In one embodiment, each retention passage includes a spiral section winding axially about an axis between spiral end portions. A nozzle passage is connected to the one of the spiral end portions and extends axially toward the other spiral end portion to prevent drainage of the liquid from a cavity in the valve that is connected to the other spiral end portions. 
   The ecology/flow divider valve has a pressure actuated piston slidably disposed within the valve body and is movable between a position corresponding to engine shut-down and a second position corresponding to engine operation. Spring means bias the piston toward the shut-down position. The piston forms the cavity as it moves. The cavities are sized such that fluid in a nozzle passage is pulled into a cavity when the piston moves from the operating position to the shut-down position. 
   Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which: 
       FIG. 1   a  is a cross-sectional view of the valve of the present invention with the valve in a deactivated position; 
       FIG. 1   b  is a cross-sectional view of the valve of  FIG. 1   a  taken along line  1   b;    
       FIG. 1   c  is the cross-sectional view of the valve of  FIG. 1   a  rotated 180 degrees along line  1   b;    
       FIGS. 2-4  are cross-sectional views of the valve of the present invention showing the sequential positioning of the piston of the valve as it moves from a deactivated (engine shutdown) position to a fully activated (engine operating) position; 
       FIG. 5  is a cross-sectional view of the valve of the present invention showing a position of the valve as the valve moves from the fully activated position to the deactivated position; 
       FIG. 6  illustrates the valve of the present invention installed at various locations around the circumference of the engine; and 
       FIGS. 7-9  are cross-sectional views of an alternate embodiment of the valve of the present invention showing the sequential positioning of the piston of the valve as it moves from a deactivated position to a fully activated position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning to the drawings, wherein like reference numerals refer to like elements, the invention is illustrated as being implemented in a suitable environment. As illustrated in  FIG. 1   a , the fuel system described herein generally comprises a plurality of fuel nozzles  100  arranged in a combustion chamber  102 , a fuel metering unit  104 , and a fuel manifold  106  disposed therebetween. It will be understood by those skilled in the art that the fuel metering unit  104  includes a pressurizing, shutoff, and drain valve  108  which delivers fuel to the fuel nozzles  100  once a predetermined start-up pressure is attained, and a metering valve (not shown) which modulates the fuel flow rate to the fuel nozzles  100  thereafter. It will also be understood that the fuel manifold  106  comprises any means which provides a fluidic connection between the fuel metering unit  104  and the fuel nozzles  100 . 
   Flow is metered by the fuel control and passes into the engine fuel manifold  106  through the fuel control pressurizing, shutoff, and drain valve  108 . The fuel manifold  106  supplies fuel to many nozzle assemblies. Each nozzle assembly  110  may have multiple nozzle tips. In the description that follows, two nozzle tips  112 ,  114  in the nozzle assembly  110  shall be used to describe the invention. 
   The nozzle assembly  110  has nozzle passages  116 ,  118  that connect the nozzle tips  112 ,  114  to ecology cavities  120 ,  122  via retention passage  124 ,  126  around the flow divider/ecology valve  130 . For clarity, retention passage  124  is illustrated as having sections  124   1  and  124   2  and retention passage  126  is illustrated as having sections  126   1  and  126   2 . The subscript nomenclature (e.g.,  124   1 ,  124   2 ) is merely used to show the grooves.  124   1  and  126   1  are on the near side of sleeve  146  and grooves  124   2  and  126   2  are on the far side of sleeve  146 . In the embodiment shown, retention passage  124 ,  126  is a 360 degree spiral groove. Any other retention passage may be used that is equivalent to the spiral groove (i.e., a geometry that requires the fuel to flow “uphill” to exit the valve  130 ). The flow divider/ecology valve  130  has shut-off and ecology piston  132  and flow divider valve  134  that are held to a closed position via springs  136 ,  138 . Piston  132  acts to shut off fuel to both nozzle tips  112 ,  114  and provides the variable volume ecology cavities for both tips. Valve  134  opens to regulate the flow division or split between the nozzle tips. When the fuel metering unit pressurizing valve  108  is closed and the fuel system is unpressurized, the flow divider/ecology valve  130  will be in the position shown in  FIG. 1   a . The two springs  136 ,  138  in the assembly hold the two flow divider valves  132 ,  134  closed. An elastomeric face seal  140  (i.e., o-ring) prevents leakage from the manifold  106  to either of the nozzle tips  112 ,  114 . Any fuel in the manifold  106  flows to the fuel tank connection  142 . 
   The nozzle passages  116 ,  118  are bored in housing  144 . The retention passages  124 ,  126  are formed on the inner wall of the housing  144  or on the outer wall of sleeve  146  inserted into housing  144 . The cavities  120 ,  122  are formed within the sleeve  146 . In the embodiment illustrated in  FIGS. 1-9 , the retention passages are formed on the outer wall of sleeve  146 . 
   Turning now to  FIG. 2 , the valve assembly position during starting is shown. The fuel metering unit pressurizing valve  108  has opened and metered flow is being supplied to the fuel manifold  106  as indicated by arrow  150 . The connection  142  to the fuel tank is blocked by the pressurizing valve  108 . Fuel pressure builds and overcomes the force of the nozzle spring  138  and moves the piston  152  of valve  132  to the right. As the piston  152  translates, fuel that is in ecology cavities  120 ,  122  is displaced from the ecology cavities  120 ,  122  that fills the passages  116 ,  118  leading to the nozzle tips  112 ,  114 . The flow displaced from cavities  120 ,  122  flows through the retention passage  124 ,  126  before filling the nozzle passages  116 ,  118 . This retention passage  124 ,  126  retains fuel in all nozzle locations around the engine circumference. The retention passage  124 ,  126  allows the installation of the same nozzle assembly at any location around the circumference of the engine, thereby reducing cost since only one type of nozzle assembly is manufactured. 
   When the piston  152  moves further to the right as illustrated in  FIG. 3 , port  154  is opened. When port  154  is opened, metered flow is provided to nozzle tip  112 . The nozzle valve  134  remains closed until metered flow is increased by the fuel control and pressure builds. As the piston  152  moves to the right, the volume of ecology cavity  120  diminishes and any fuel in the ecology cavity  120  that is displaced by the movement of piston  152  flows into nozzle passage  116 . 
   Turning now to  FIG. 4 , as fuel flow continues to increase, the fuel control fuel pressure will build until it reaches a point where the divider valve  134  opens. Fuel then flows into cavity  122  and to nozzle  114  via port  158 , retention passage  126  and nozzle passage  118 . Flow division between nozzle  112  and nozzle  114  is determined by the valve port areas, spring forces, and nozzle tip orifice areas. The flow division is known in the art and need not be discussed here. 
   Turning now to  FIG. 5 , as the fuel flow decreases, the fuel pressure lowers. When the pressure gets low enough where the spring force is greater than the pressure force, divider valve  134  closes, leaving only nozzle  112  flow. When fuel is selected off by the operator, the pressurizing valve  108  closes. The closing of the valve  108  shuts off fuel to the manifold  106  and simultaneously connects the fuel manifold  106  to the fuel tank via passage  142 . This allows the nozzle assembly piston  152  to move to the left as a result of the fuel pressure becoming lower than the force of the spring  138 . The movement of the piston  152  to the left creates a suctioning effect that results in fuel being pulled from nozzle passages  116 ,  118  into the two fuel cavities  120 ,  122  as the piston  152  moves towards the closed position. Removal of the fuel from the hot passages  116 ,  118  of each nozzle prevents coking of the fuel in the hot passages  116 ,  118 . 
   As previously indicated, the retention passage  124 ,  126  retains fuel in all nozzle locations around the engine circumference, which provides the ability to locate the valve in any position with respect to gravity. For example,  FIG. 1   b  illustrates the valve positioned with respect to gravity such that all the fuel pulled from the nozzle and nozzle passages during engine shutdown as described below is all pulled into the ecology cavities.  FIG. 1   c  illustrates the valve positioned with respect to gravity such that a portion of the fuel pulled from the nozzle and nozzle passages remains in the retention passage when the engine is shut down. 
     FIG. 6  shows a simplified representation of the valve of the invention at four positions around the circumference of combustion chamber  102  with the valves  132 ,  134  in the closed position as represented by block  210 . For purposes of illustration, only ecology cavity  122  and nozzle passage  118  are shown and the direction of gravity is illustrated by arrow  208 . Valve  200  is at a “12 o&#39;clock” position, valve  202  is at a “3 o&#39;clock” position, valve  204  is at a “6 o&#39;clock” position, and valve  206  is at a “9 o&#39;clock” position. With adequate piston translation to pull a small amount of air into each ecology cavity  120 ,  122 , the assembly  100  can be tilted in any position and the fluid in the cavity will have to flow “up hill” through the spiral groove  124 ,  126  to get out of the assembly  110 . The “up-hill” flow prevents fluid from dripping out of the ecology cavities  120 ,  122 . For example, fluid has to travel “up-hill” through section  126   2  in valve  200  before flowing into the chamber  102 . Fluid must travel “up-hill” through section  126   1  in valve  202  before flowing into chamber  102 . In valve  204 , fluid in cavity  122  must flow up to retention passage port  158  before it can flow down to nozzle passage  118  and then it must flow “up-hill” in nozzle passage  118  to reach the combustion chamber  102 . In valve  206 , fluid in cavity  122  must flow up to retention passage port  158  before it can flow down to section  126   1  and then it must flow “up-hill” in section  126   2  before it can reach the combustion chamber  102  via nozzle passage  118 . 
   Turning now to  FIGS. 7-9 , an alternate embodiment of the present invention is illustrated. In this embodiment, two independent pistons  300 ,  302  are used for the ecology function. This design allows each manifold to be filled and drained independently. This has the advantage of keeping nozzle passage  118  empty (i.e., dry) until just before flow is desired in nozzle  114 . When the fuel metering unit pressurizing valve  108  has opened, metered flow is being supplied to the fuel manifold  106  as indicated by arrow  150 . The connection  142  to the fuel tank is blocked by the pressurizing valve  108 . Fuel pressure builds and overcomes the force of the nozzle spring  136  and moves the piston  300  to the right. As the piston  300  translates, fuel that is in ecology cavity  120  is displaced and flows into passage  116  via port  304  of cavity  120 . 
   When the piston  300  moves further to the right as illustrated in  FIG. 8 , piston  300  will eventually reach the fully actuated position and port  304  will close and port  306  will open. When port  306  is opened, metered flow is provided to nozzle tip  112 . Piston  302  remains closed until metered flow is increased by the fuel control and pressure builds. When pressure is high enough to overcome the force of spring  138 , piston  302  will begin to move to the right and fuel in cavity  122  will flow through port  308  and into the retention passage  126  via port  158 . 
   Turning now to  FIG. 9 , as fuel flow continues to increase, the fuel pressure will build until it reaches a point where the port  310  opens. Fuel then flows into retention passage  126  and to nozzle  114  via port  310  and port  156 . Upon shutdown, the system works similar to the first system described. As the fluid pressure decreases, the force of the springs  136 ,  138  will eventually be higher than the fluid pressure and the pistons  300 ,  302  will move to the left. The movement of the piston  300 ,  302  to the left creates a suctioning effect that results in fuel being pulled from nozzle passages  116 ,  118  into the two fuel cavities  120 ,  122  via ports  304 ,  308  as the pistons  300 ,  302  move towards the closed position. The springs may be sized such that one of the pistons  300 ,  302  begins to move towards the closed position before the other piston. 
   The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
   Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.