Abstract:
A dual function rapid shutdown and ecology system for fuel delivery systems for engines, specially aircraft gas turbine engines, is disclosed. The dual function is accomplished in a single module operated by a single electromagnetic solenoid valve commanded by the engine electronic control unit. Upon actuation of the solenoid valve, a large spring loaded piston strokes to the extreme of its travel creating a cavity having a volume sufficient to accommodate all fuel leftover in the fuel manifold and distribution system at shutdown, thus preventing atmospheric pollution or engine damage upon subsequent operation. Simultaneous with actuation of the solenoid valve, fuel pressure differentials cause a small piston to stroke to the extreme of its travel opening fuel passageways and causing all the fuel being delivered to the engine combustion chamber to be bypassed back to pump inlet, thus effectively accomplishing the rapid shutdown function. An alternate embodiment allows for use of the dual function system on engines employing low pressure differentials along the various stages of the fuel control system manifold or where the ecology function is not required.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to fuel delivery systems for engines, especially aircraft gas turbine engines, and, more particularly, to a dual function rapid shutdown and ecology system for such fuel delivery systems, which performs its function upon engine shutdown.  
           [0002]    Two of the functions provided by the fuel control system of a gas turbine engine are fuel shutoff/turn-on and ecology fuel management. The first function, fuel shutoff/turn-on, may be manually commanded from the control system (for instance, by the pilot for aircraft applications), or it may be triggered automatically through an overspeed detection system provided by the engine&#39;s electronic control. In the later case, the response of the system must be extremely fast so as to limit the engine speed excursions above the normal operating range.  
           [0003]    A second function of the fuel control system is ecology management, and requires that the fuel in the manifold be disposed of properly during shutdown and not be allowed to drain into the engine where it will vaporize and/or smoke when in contact with the still-hot combustion chamber, thereby creating atmospheric pollution. Also, after any type of shutdown, it is necessary that fuel remaining in the engine fuel manifold be removed rapidly to keep it from puddling. Fuel left in the manifold can cause hot starts upon subsequent engine operation and will also coke the engine&#39;s fuel nozzles, a condition which hinders nozzle performance, leading to premature failure.  
           [0004]    An examination of prior art shows that there have been many and varied attempts to address one or both of the aforementioned fuel control system functions. Of particular interest in this regard are the following references and examples:  
           [0005]    U.S. Pat. No. 4,206,595 discloses a system to collect fuel left over in the fuel manifold upon engine shutdown and reintroduce it on the next engine start. The system uses two check valves, two springs and two pistons to accomplish this function.  
           [0006]    U.S. Pat. No. 5,809,771 teaches a system which uses flow divider differential pressure to remove fuel from the fuel manifold upon engine shutdown and which temporarily stores the fuel until the engine is subsequently restarted.  
           [0007]    U.S. Pat. No. 6,195,978 B1, assigned to the assignee of this application, involves a system whereby fuel flow is reversed upon engine shutoff by adding one valve to the main fuel control and modifying the main fuel control pressurizing valve to include a pressure switch function. The invention is also directed toward gas turbine engines that include both primary and secondary manifold systems.  
           [0008]    U.S. patent application Ser. No. 09/361,932, also assigned to the assignee of this application, discloses a fuel divider and ecology system adapted for engines requiring three discrete fuel manifolds. The ecology function is accomplished using one single chamber staged valve and modifying the main fuel control pressurizing valve to include a pressure switching function.  
           [0009]    Various other prior art fuel systems have addressed fuel shutoff/turn-on concerns as well as ecology issues and have introduced various other techniques in an effort to control both problems. Examples include: draining fuel overboard after engine shutdown, blowing unburned fuel into and through the engine at shutdown, and draining unburned fuel into a tank that must be manually emptied.  
           [0010]    None of the above cited prior art provide a single, simple, module that accomplishes the dual functions of rapid shutoff (or turn on) of fuel flow as well as ecology management.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention accomplishes the dual function of rapid shutdown and ecology management in a single module operated by a single electromagnetic solenoid valve. In one aspect of the present invention, a cylindrically shaped valve body is provided to house a large spring loaded piston member, which when extended due to pressure differentials caused by actuation of the solenoid valve, provides sufficient volume to accommodate all fuel left over in the fuel manifold and distribution system at shutdown. Simultaneously, a secondary small piston member, which is housed internal to the underside of the large piston member, also actuates causing all fuel being delivered to the engine combustion chamber to be bypassed back to pump inlet.  
           [0012]    In another aspect of the present invention, separate cylindrically shaped valve bodies are provided to house the large spring loaded piston member and the small piston member. This alternate embodiment is intended for use on fuel control systems employing low pressure differentials along various stages of the fuel control system manifold. The large spring loaded piston member extends at low pressure differentials caused by actuation of the solenoid valve, and provides sufficient volume to accommodate all fuel left over in the fuel manifold and distribution system at shutdown. A small accumulator, or alternatively a check valve, is provided to accommodate a small amount of fuel displaced upon actuation of the large piston member. Simultaneously, with actuation of the solenoid valve, the remotely located small piston member, also actuates causing all fuel being delivered to the engine combustion chamber to be bypassed back to pump inlet.  
           [0013]    These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of embodiments of the invention when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic and partial cross sectional representation of a gas turbine engine fuel control system, including an embodiment of the inventive rapid shutdown and ecology system, shown in its first position during engine operation;  
         [0015]    [0015]FIG. 2 is a similar schematic and partial cross sectional representation of a gas turbine engine fuel control system, including an embodiment of the inventive rapid shutdown and ecology system, shown in its second position at engine shut down;  
         [0016]    [0016]FIG. 3 is a schematic and partial cross sectional representation of a gas turbine engine fuel control system, including an alternate embodiment of the inventive rapid shutdown and ecology system, shown in its first position during engine operation; and  
         [0017]    [0017]FIG. 4 is a similar schematic and partial cross sectional representation of a gas turbine engine fuel control system, including an alternate embodiment of the inventive rapid shutdown and ecology system, shown in its second position at engine shut down. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The following detailed description is for the best currently contemplated methods for carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention.  
         [0019]    In order to fully appreciate this invention, it is best to describe the details of the component parts in connection with the operational modes of the gas turbine engine&#39;s fuel control system. In this light the descriptions that follow address both engine operation and shutdown modes for two embodiments of the inventive rapid shutdown and ecology system.  
         [0020]    In FIG. 1, an illustrative gas turbine engine fuel control system  10  of a mostly conventional configuration known to those skilled in the art includes fuel supply  11  originating from fuel tanks (not shown) entering a low pressure fuel pump  12 , which increases the pressure in line  13  to level Po. Fuel then proceeds to high pressure pump  14 , which further increases fuel pressure to level P1 in line  15 , at which point it enters metering valve  16  for modulating the rate of flow from the fuel supply to the combustor atomizers (not shown). Fuel pressure in line  15 A downstream of metering valve  16  decreases to level P2 (by the setting of bypass valve  18 ) and thereafter further decreases to level P3 in line  22  after passing through pressurizing valve  21 , which controls and establishes a minimum pressure of fuel delivered to the combustor atomizers downstream of flow arrow  23 . The bypass valve  18  returns, via lines  19  and  20 , pump flow in excess of metered flow and also controls fuel pressure such that P1 is always higher than P3, usually about 25 psi or greater. Additionally, at low fuel flow rates, P1 will be additionally higher than P3 by the setting of pressure rising valve  21 . Orifice  19 A is provided on line  19  to create a damping pressure drop to stabilize bypass valve  18 . All functions of the gas turbine engine fuel control system  10  are commanded by the engine electronic control unit (ECU), which is not shown on the drawings, by repositioning the metering valve  16 .  
         [0021]    The inventive rapid shutdown and ecology system  24  communicates with line  22  by means of line  25 , and is positioned to be downstream of pressure rising valve  21  and upstream of the combustor atomizers. It is comprised of a metallic cylindrically shaped valve body  26  internally bored to define valve chamber  27  having an upper end  28  and an a lower end  29  at the longitudinal extremities. A large piston member “B”  30  is movable along the longitudinal axis of the valve chamber  27  between upper end  28  and lower end  29 . The flat surface of large piston member “B”  30  at the upper end  28  is bored to form fuel cavity “B”  31 . The depth and diameter of said fuel cavity “B”  31  are sized to provide a scavenge volume sufficient to accommodate all fuel in the fuel control system  10  downstream of pressure rising valve  21 , when the large piston member “B”  30  has moved to the extreme of its stroke in the direction of lower end  29 . A spirally wound spring  32  is positioned along the axial periphery of fuel cavity “B”  31 , such that when compressed, one end bears on upper end  28  and the other end bears on the base of fuel cavity “B”  31 . Spring  32  is designed to remain fully compressed when fuel pressure Px in fuel cavity “A”  34  is sufficiently greater than P3, the pressure immediately downstream of pressure rising valve  21 . In other words, the difference between Px and P3 times the area of piston B must be greater than the load in spring  32 . O-ring seals  44  are provided at three circumferential levels to prevent fuel flow between the inner surface of valve chamber  27  and the exterior surface of large piston member “B”  30  when the latter strokes along the longitudinal axis of valve chamber  27 .  
         [0022]    Small piston member “A”  33  is placed internal to a close tolerance cylindrically bored cavity  36  located along the longitudinal centerline of large piston member “B”  30  at lower end  29 . Small piston member “A”  33  may be equipped with an o-ring seat  45  to prevent any leakage of metered fuel during normal engine operation. Face plate  35 , secured to large piston member “B”  30 , interlocks small piston member “A”  33  within bored cavity  36 . Two fuel passages extending from bored cavity upper end  36 A provide communication with elements of the fuel control system  10  manifold as follows: Passageway  37  leads to annular cavity  37 A on valve body  26 , and then to line  38 , thus permitting free flow of fuel from downstream of metering valve  16  to small piston member “A”  33  at the bored cavity upper end  36 A. Fuel passageway  39  leads to annular cavity  39 A on valve body  26 , and then via line  40  to line  13  downstream of the low pressure fuel pump  12 . Electro-magnetic solenoid valve  41 , which is commanded by the ECU, connects line  40  with fuel cavity “A” at lower end  29 . On the opposite side of valve body  26 , line  42  connects fuel cavity “A”  34  with line  15 , immediately downstream of high pressure pump  14 . A small orifice  43  is provided on line  42  to establish a pressure drop from P1 to Px when solenoid valve  41  is open. For one embodiment, diameter  46  of large piston member “B”  30  is about 2.5 inches and stroke  47  is about 1.5 inches. Those dimensions will vary as a function of the specific gas turbine engine&#39;s fuel control system configuration.  
         [0023]    Still referring to FIG. 1, the fuel control system is shown in its first position during engine operation. Solenoid valve  41  is closed and pressure in fuel cavity “A”  34 , Px, is equal to P1, which is always higher than P3 (by at least about 25 psi). Accordingly, large piston member “B”  30  is fully stroked toward upper end  28 , and spring  32  is fully compressed. Simultaneously, since Px is higher than P2, small piston member “A”  33  is fully stroked toward bored cavity upper end  36 A, thus preventing fuel flow from line  38  to line  40 . Therefore, during engine operation, the inventive rapid shutdown and ecology system remains inoperative.  
         [0024]    Referring now to FIG. 2, there is shown the same gas turbine engine fuel control system schematic as in FIG. 1 with the exception that the embodiment of the inventive rapid shutdown and ecology system  10  is now shown in its second position at engine shut down. It is at this phase that it accomplishes its intended dual function of rapid shutoff (or turn on) of fuel flow as well as ecology fuel management.  
         [0025]    When the gas turbine engine is shut down either by manual command from the control system (for instance, by the pilot for aircraft applications) or automatically through an overspeed, overtemperature or other fault detection system, the ECU opens solenoid valve  41  and shortly thereafter, when P2 falls below a predetermined level, pressure rising valve  21  closes. Closure of pressure rising valve  21  terminates fuel delivery to the combustor atomizers and opening of solenoid valve  41  immediately establishes a communication path between the upstream and downstream sides of high pressure pump  14  (via line  42 , fuel cavity “A”  34 , solenoid valve  41 , and line  40 ). Due to the pressure drop of orifice  43 , fuel pressure in fuel cavity “A”  34 , Px, thus drops to Po, causing spring  32  to shift large piston member “B”  30  to the extreme of its stroke in the direction of lower end  29 . This action increases the volume of fuel cavity “B”  31  thereby collecting all the fuel in the fuel control system  10  downstream of pressure rising valve  21 , and preventing it from draining into the engine creating atmospheric pollution and/or puddling, causing hot starts upon subsequent engine operation.  
         [0026]    Simultaneously with the reduction of Px to Po, small piston member “A”  33  moves toward lower end  29 , thus establishing an open communication path between passageways  37  and  39 , annular cavity  39 A, and line  40 . In addition, as the pressure in lines  37 ,  38  and  19  fall to the Po level the bypass valve  18  moves toward orifice  19 A. These actions cause all of the fuel being delivered to the chamber atomizers to be immediately bypassed back to the high pressure pump  14  inlet, either through the bypass valve itself or through piston “A” cavity upper end  36 A. The rapid shutoff of fuel flow to the engine has therefore been achieved.  
         [0027]    When solenoid valve  41  is again closed by ECU command, the reverse process takes place. Fuel cavity “A” pressure Px increases to P1 forcing small piston member “A”  33  to move toward bored cavity upper end  36 A, closing passageway  39  and terminating the fuel bypass condition. Large piston “B”  30  also moves toward upper end  28 , compressing spring  32 , and forcing the fuel previously collected in fuel cavity “B”  31  to return to the fuel control system manifold downstream of pressure rising valve  21 . Rapid turn on of fuel flow to the engine has therefore been achieved and atmospheric pollution has been prevented.  
         [0028]    On some gas turbine engine fuel control systems, the setting of bypass valve  18  is quite low and pressure rising valve  21  is referenced to Po rather than P2. Under those conditions, the difference between P1 and P3 is insufficient to compress spring  32  and hold large piston member “B”  30  fully stroked toward upper end  28 , as shown in FIG. 1. To accommodate those conditions and still provide the intended dual function of rapid shut down (or turn on) of fuel flow as well as ecology fuel management, another embodiment of the inventive rapid shut down and ecology system has been devised and is shown on FIGS. 3 and 4.  
         [0029]    In FIG. 3, another embodiment of the inventive rapid shutdown and ecology system is shown in its first position during engine operation. The gas turbine engine fuel control system  10  is the same as that shown of FIGS. 1 and 2, and is comprised of the same conventional components, including low pressure fuel pump  12 , high pressure pump  14 , metering valve  16 , bypass valve  18 , pressurizing valve  21 , and various inter-communicating fuel lines, and all functions are commanded by the engine electronic control unit (ECU).  
         [0030]    The other embodiment is comprised of two separately functioning subsystems, one for the ecology management function  48 A and another for the rapid shutdown function  48 B. The ecology management subsystem is shown to the right of view line A-A, and may be remotely located from the remaining fuel control system. It is comprised of a cylindrically shaped valve body  49  internally bored to define valve chamber  50  having an upper end  52  and an a lower end  53  at the longitudinal extremities. A large piston member “B”  51  is movable along the longitudinal axis of valve chamber  50  between upper end  52  and lower end  53 . The flat surface of large piston member “B”  51  at the upper end  52  is bored to form fuel cavity “B”  54 . The depth and diameter of said fuel cavity “B”  54  are sized to provide a scavenge volume sufficient to accommodate all fuel in the fuel control system  10  downstream of pressure rising valve  21 , when the large piston member “B”  51  has moved to the extreme of its stroke in the direction of lower end  53 . A spirally wound spring  55  is positioned along the axial periphery of fuel cavity “B”  54 , such that when compressed, one end bears on upper end  52  and the other end bears on the base of fuel cavity “B”  54 . Spring  55  is designed to remain fully compressed when fuel pressure Px, in fuel cavity “A”  57 , acting on piston diameter “A”  59  produces a force which is greater that the force produced by pressure P3 acting on the smaller piston diameter “B”  58 .  
         [0031]    When large piston member “B”  51  is in contact with upper end  52  during engine operation, fuel leakage from P3 to Px is prevented by circumferential o-ring seal  56  and annular o-ring seal  60 . Under this condition, the small amount of fuel displaced into large piston annular cavity  66  is routed via fuel port  61  into a small, spring loaded, accumulator valve  62  where it is temporarily stored until engine shut down, at which time the spring load forces its return to fuel cavity “B”  54 . A “witness” drain  63  is provided to collect any inadvertent fuel leakage past accumulator valve  62 . An alternate embodiment involves use of a spring loaded check valve  64  in lieu of accumulator valve  62 . In such a case, the displaced fuel is released via line  65  to any fuel line, such as line  40 , having pressure Po.  
         [0032]    For another embodiment of the ecology management subsystem  48 A, piston diameter “A”  59  is about 2.5 inches and piston diameter “B”  58  is about 2.0 inches, while stroke  51 A is about 1.5 inches. Those dimensions will vary as a function of the specific gas turbine engine&#39;s fuel control system configuration.  
         [0033]    Still referring to FIG. 3, the rapid shutdown subsystem  48 B is comprised of a metallic cylindrically shaped valve body  67  internally bored to define valve chamber  68  and having an upper end  69  and a lower end  70 . A closely fitting cylindrically shaped small piston  71  placed internal to valve body  67  and is movable along the longitudinal axis of valve chamber  68  between the upper end  69  and the lower end  70 . An o-ring seal  72  is fitted along the periphery of small piston  70  to prevent fuel passage between upper  69  and lower  70  ends of valve chamber  68 .  
         [0034]    The rapid shutdown subsystem  48 B communicates with the ecology subsystem  48 A and other elements of the fuel control system  10  by means of the following fuel lines: Line  73  is connected to line  15  downstream of high pressure pump  14  and leads to solenoid valve  74  (which is commanded by the ECU) and then to fuel cavity “A”  57  of the ecology subsystem  48 A. An orifice  75  is provided to create a pressure drop from P1 to PX when the solenoid valve  74  is open. Line  76  connects line  73  to valve body  67 , thus exposing the lower end  70  of small piston  71  to pressure P1. Line  77  connects to line  15 A and exposes the upper end  69  of small piston  71  to pressure P2, which is lower than P1. Finally, line  79  communicates between the upper end  69  of valve body  67  and line  13 , immediately downstream of low pressure pump  12 , which is at pressure Po, and line  78  connects line  79  to solenoid valve  74 .  
         [0035]    The fuel control system as shown in FIG. 3 is in its first position during engine operation. Solenoid valve  74  is closed and pressure in fuel cavity “A”  57 , Px, is equal to P1 by virtue of fuel flow through line  73 . Accordingly, large piston member “B”  51  is fully stroked toward upper end  52 , and spring  55  is fully compressed. Simultaneously, since Px is higher than P2, small piston  71  is fully stroked toward the upper end  69 , thus preventing fuel flow from line  77  (pressure P2) to line  79  (pressure Po). Therefore, during engine operation, the other embodiment of the inventive rapid shutdown and ecology system remains inoperative.  
         [0036]    Referring now to FIG. 4, there is shown the same gas turbine engine fuel control system schematic as in FIG. 3 with the exception that the other embodiment of the inventive rapid shutdown and ecology system  10  is now shown in its second position at engine shut down. It is at this phase that it accomplishes its intended dual function of rapid shutoff (or turn on) of fuel flow as well as ecology fuel management.  
         [0037]    When the gas turbine engine is shut down either by manual command from the control system (for instance, by the pilot for aircraft applications) or automatically through an overspeed, overtemperature or other fault detection system, the ECU opens solenoid valve  74  and shortly thereafter, when P2 falls below a predetermined level, pressure rising valve  21  closes. Closure of pressure rising valve  21  terminates fuel delivery to the combustor atomizers and opening of solenoid valve  74  immediately establishes a communication path between the upstream and downstream sides of high pressure pump  14  (via line  73 , solenoid valve  74 , and lines  78  and  79 ). Fuel pressure in fuel cavity “A”  57 , Px, thus drops to Po, causing spring  55  to shift large piston member “B”  51  to the extreme of its stroke in the direction of lower end  53 . This action increases the volume of fuel cavity “B”  54  thereby collecting all the fuel in the fuel control system  10  downstream of pressure rising valve  21 , and preventing it from draining into the engine creating atmospheric pollution and/or puddling, causing hot starts upon subsequent engine operation.  
         [0038]    Simultaneously, at rapid shutdown subsystem  48 B, with the reduction of Px to Po, small piston  71  moves toward lower end  70 , thus establishing an open communication path between line  77  and line  79 . In addition, as the pressure in lines  77  and  19  fall to the P0 level the bypass valve  18  moves toward orifice  19 A. These actions causes all of the fuel being delivered to the chamber atomizers to be immediately bypassed back to the high pressure pump  14  inlet, either through the bypass valve itself or through piston “A” cavity upper end  69 . The rapid shutoff of fuel flow to the engine has therefore been achieved.  
         [0039]    When solenoid valve  74  is again closed by ECU command, the reverse process takes place. Fuel cavity “A”  57  pressure Px increases to P1 forcing small piston  71  to move toward upper end  69 , stopping flow through line  77  thus terminating the fuel bypass condition. On the ecology management subsystem,  48 A, large piston member “B”  51  also moves toward upper end  52 , compressing spring  55 , and forcing the fuel previously collected in fuel cavity “B”  54  to return to the fuel control system manifold downstream of pressure rising valve  21 . Rapid turn on of fuel flow to the engine has therefore been achieved and atmospheric pollution has been prevented.  
         [0040]    The other embodiment also has the advantage that the ecology and rapid shutdown features can be separated, along line A-A of FIGS. 3 and 4, in the event the ecology function is not required, such as on military engines.  
         [0041]    Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained therein.