Abstract:
A fuel valve for a gas turbine engine includes a passageway configured to direct a fuel to the engine and a flow restriction positioned in the passageway. The fuel valve may also include a first pressure sensor coupled to the passageway upstream of the restriction through an upstream port, and a second pressure sensor coupled to the passageway downstream of the restriction through a downstream port. The fuel valve may further include a third pressure sensor coupled to the upstream port through a first branch port, and a fourth pressure sensor coupled to the downstream port through a second branch port.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to fuel control system for a gas turbine engine, and particularly to fuel valve with backup flow measurement capability. 
       BACKGROUND 
       [0002]    In a typical gas turbine engine, fuel is combusted in a combustion chamber (called combustor) to produce high pressure combustion gases. These high pressure gases are then used to spin the rotors of a turbine to produce power. Various types of fuel, such as natural gas or diesel fuel, may be combusted in a gas turbine engine to produce power. To control the amount of power produced by the turbine engine, the quantity of fuel directed to the gas turbine engine is controlled. For efficient operation of the turbine engine it is desirable to know the amount of fuel directed to the turbine engine at any time. Methods of determining fuel flow to a gas turbine engine are known in the art. For example, U.S. Pat. No. 7,069,137 describes an exemplary fuel flow measurement method for a gas turbine engine. The method of the &#39;137 patent includes using a variable flow metering device including a plurality of sensors to determine the fuel flow to the turbine engine. 
       SUMMARY 
       [0003]    In one aspect, a fuel valve for a gas turbine engine is disclosed. The fuel valve includes a passageway configured to direct a fuel to the engine and a flow restriction positioned in the passageway. The fuel valve may also include a first pressure sensor coupled to the passageway upstream of the restriction through an upstream port, and a second pressure sensor coupled to the passageway downstream of the restriction through a downstream port. The fuel valve may further include a third pressure sensor coupled to the upstream port through a first branch port, and a fourth pressure sensor coupled to the downstream port through a second branch port. 
         [0004]    In another aspect, a method of measuring a quantity of fuel flowing to a gas turbine engine is disclosed. The method includes directing the fuel to the engine through a flow restriction positioned in a passageway and measuring the quantity of fuel flowing through the passageway based on measurements of a first pressure sensor and a second pressure sensor. The first pressure sensor may be coupled to the passageway upstream of the restriction through an upstream port and the second pressure sensor may be coupled to the passageway downstream of the restriction through a downstream port. The method may also include independently measuring the quantity of fuel flowing through the passageway based on measurements of a third pressure sensor coupled to the upstream port through a first branch port, and a fourth pressure sensor coupled to the downstream port through a second branch port. 
         [0005]    In yet another aspect, a fuel control system for a gas turbine engine is disclosed. The control system may include a conduit configured to direct a fuel to a combustor of the gas turbine engine, and a flow valve including a flow restriction. The flow valve may include a first pressure sensor configured to measure a pressure upstream of the restriction, a second pressure sensor configured to measure a pressure downstream of the restriction, and an electronics module configured to measure a quantity of fuel flowing in the conduit based on the measurements of the first and the second pressure sensor. The control system may also include a third pressure sensor configured to measure the pressure upstream of the restriction independent of the first pressure sensor, and a fourth pressure sensor configured to measure the pressure downstream of the restriction independent of the second pressure sensor. The control system may be configured to receive a value indicative of the measured quantity of fuel from the electronics system, and independently determine the quantity of the fuel flowing in the conduit based on the measurements of the third and the fourth pressure sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cutaway-view illustration of an exemplary disclosed gas turbine engine; 
           [0007]      FIG. 2  is a schematic illustration of an exemplary control system of the gas turbine engine of  FIG. 1 ; 
           [0008]      FIG. 3A  is a schematic illustration of an exemplary fuel valve of the gas turbine engine of  FIG. 1 ; 
           [0009]      FIG. 3B  is a perspective view of an exemplary fuel valve of the gas turbine engine of  FIG. 1 ; and 
           [0010]      FIG. 4  is a flow chart illustrating an exemplary operation of the gas turbine engine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  illustrates an exemplary gas turbine engine  100 . Gas turbine engine  100  may have, among other systems, a compressor system  10 , a combustor system  12 , a turbine system  14 , and an exhaust system  16 . In general, compressor system  10  compresses air to a high pressure and directs the compressed air to combustor system  12 . A gaseous fuel and a liquid fuel are directed to the combustor system  12  through a gaseous fuel pipe  22  and a liquid fuel pipe  24 , respectively. One or more of these fuels are mixed with the compressed air in fuel injectors  30  and combusted in a combustor  18  of the combustor system  12 . Since both a liquid fuel and a gaseous fuel may be selectively directed to combustor  18  through fuel injectors  30 , gas turbine engine  100  is commonly called a dual fuel gas turbine engine, and fuel injectors  30  are commonly called dual fuel injectors. Combustion of the fuel in combustor  18  produces combustion gases at a high pressure, temperature, and velocity. These combustion gases rotate rotors of the turbine system  14  to generate power. The spent combustion gases are then exhausted to the atmosphere through exhaust section  16 . 
         [0012]    Various types of gaseous and liquid fuels may be directed into combustor  18  through fuel injectors  30 . The gaseous fuel may include, for example, natural gas, landfill gas, bio-gas, syngas, etc. The liquid fuels may include diesel, kerosene, gasoline, or any other type of liquid fuel. In some applications, the gas turbine engine  100  may be operated primarily using a fuel that is cheaply available at the location where the gas turbine engine  100  is operating. For example, in an oil field with an abundant supply of natural gas, the gas turbine engine  100  may operate primarily using natural gas. In such applications, liquid fuel may be reserved for engine operating conditions where a liquid fuel may be more desirable. For instance, a liquid fuel may be directed to gas turbine engine  100  during startup and when combustion instabilities are detected in the combustor  18 . After the gas turbine engine  100  reaches a stable operating condition, the liquid fuel supply to the turbine engine  100  may be turned off, and the gaseous fuel supply turned on. 
         [0013]      FIG. 2  is a schematic illustration of a fuel flow system of gas turbine engine  100 . The fuel flow system may include a control system  60  configured to control the fuel flow to the gas turbine engine  100 . For example, based on power requirements, control system  60  may control the amount of fuel directed to the gas turbine engine  100  through gaseous fuel pipe  22  and liquid fuel pipe  24  to produce the required power in a stable manner. Control system  60  may include a microprocessor  42 , storage memory  44 , and/or other electronic components (not shown) that operate to control the operation of gas turbine engine  100 . In addition to functions normally performed by control systems known in the art, control system  60  may also control the type and quantity of fuel directed to the gas turbine engine  100  based on operating parameters. Gaseous fuel pipe  22  and/or liquid fuel pipe  24  may be fluidly coupled to sensors and measurement devices adapted to measure parameters related to fuel flow. These measurement devices may include, among others, a fuel valve  62  that measures the amount of gaseous fuel directed to turbine engine  100  through gaseous fuel pipe  22 . In some embodiments, liquid fuel pipe  24  may also be fluidly coupled to a fuel valve  64  adapted to measure the amount of liquid fuel directed to turbine engine  100 . In some embodiments, fuel valves  62  and  64  may be a flow control device with embedded flow measurement capability. 
         [0014]    Fuel valve  62  may include any type of measurement device configured to measure one or more parameters indicative of the quantity of fuel flowing through the gaseous fuel pipe  22 . For example, fuel valve  62  may include an electronic fuel metering valve that both measures and controls the amount of fuel flowing through the fuel valve  62 . In other embodiments, these two functions may be performed by separate devices.  FIGS. 3A and 3B  illustrate views of an exemplary fuel valve  62  with embedded flow measurement capability coupled to gaseous fuel pipe  22 .  FIG. 3A  illustrates a schematic view and  FIG. 3B  illustrates a perspective view of the fuel valve  62 . In the discussion that follows, reference will be made to both  FIGS. 3A and 3B . Fuel valve  62  may include a flow metering section  66   a  and a flow measurement section  66   b . Flow metering section  66   a  may include an actuator  54  that activates a poppet valve  56  to control the amount of fuel entering the fuel valve  62  in response to signals from control system  60 . For instance, in response to instructions from control system  60 , actuator  54  may move the poppet valve  56  to increase or decrease the flow of fuel directed to the gas turbine engine  100  through the gaseous fuel pipe  22 . 
         [0015]    Flow measurement section  66   b  may include a flow restriction, such as an orifice plate  68 , adapted to measure the quantity (for example, flow rate) of fuel passing therethrough. Orifice plate  68  is a plate with a hole in the middle, positioned in the path of fuel flowing through fuel valve  62 . When the fuel reaches the orifice plate  68 , the fuel stream converges to pass through the hole. As the fuel converges, its velocity and pressure changes. Although the flow restriction is described as being an orifice plate  68 , this is only exemplary. In general, any type of flow restriction used to measure flow may be used in fuel valve  62 . As is known in the art, by measuring the difference in fluid pressure upstream and downstream of the orifice plate, the volumetric and mass flow rates of the fuel can be obtained using Bernoulli&#39;s equation. Fuel valve  62  may include an electronics module  72  that measures the difference in pressure upstream and downstream of the orifice plate  68  and computes the flow rate (or another parameter indicative of quantity) of fuel flowing through the fuel valve  62 . The electronics module  72  may include sensors, such as pressure sensors, configured to measure the pressure difference across the orifice plate  68 . These sensors may include an upstream pressure sensor  80  fluidly coupled to an upstream region of the orifice plate  68  through an upstream port  74 , and a downstream pressure sensor  82  fluidly coupled to a downstream region of the orifice plate  68  through a downstream port  76 . 
         [0016]    In some embodiments, the upstream pressure sensor  80  and/or the downstream pressure sensor  82  may be a differential pressure sensor. In embodiments where the upstream pressure sensor  80  is a differential pressure sensor, in addition to the upstream port  74  fluidly coupling the pressure sensor  80  to the upstream region of orifice plate  68 , a branch conduit  78  may fluidly couple the downstream port  76  to the pressure sensor  80 . Similarly, in embodiments where the downstream pressure sensor  82  is a differential pressure sensor, the branch conduit  78  may fluidly couple the upstream port  74  to the downstream pressure sensor  82 . Electronics module  72  may be an integral part of the fuel valve  62  and may provide the embedded flow measurement capability of fuel valve  62 . In some embodiments, as illustrated in  FIG. 3 , the integral electronics module  72  may be external to, and attached to, the fuel valve  62 . However, it is also contemplated that in some embodiments, the electronics module  72  may be internal to the fuel valve  62 . The electronics module  72  may also include other sensors  98 , such as temperature sensors, configured to measure other parameters of the fuel flowing through the fuel valve  62 . Based on the measurements of the upstream pressure sensor  80  and the downstream pressure sensor  82  (and in some embodiments, other sensors of electronics module  72 ), the flow rate of fuel flowing through the fuel valve  62  may be determined by electronics module  72 , and communicated to control system  60 . 
         [0017]    Based on the operating conditions and the required power output of gas turbine engine  100 , the control system  60  may activate actuator  54  to control the quantity of fuel directed to the gas turbine engine  100 . Measurement errors associated with one of more of the sensors of electronic module  72  may introduce errors in the fuel flow quantity determined by the electronics module  72 . Such flow measurement errors may lead to improper quantity of fuel being directed to the combustor, and thus lead to inefficient operation of gas turbine engine  100 . To minimize the likelihood of measurement errors from affecting the efficiency of the turbine engine  100 , the fuel valve  62  may be provided with redundant flow measurement capabilities. To provide redundant flow measurement capabilities, secondary pressure sensors  90  and  92  may be fluidly coupled to the upstream and downstream sections of orifice plate  68 . To ensure that fuel pressure of the same region of the fuel valve  62  is being measured by both the upstream pressure sensor  80  and the secondary pressure sensor  90 , a branch conduit  84  may fluidly couple the secondary pressure sensor  90  to the upstream port  74 . Similarly, to ensure that fuel pressure of the same region of the fuel valve  62  is measured by both the downstream pressure sensor  82  and the secondary pressure sensor  92 , a branch conduit  86  may fluidly couple the secondary pressure sensor  92  to the downstream port  76 . It is also contemplated that, in some embodiments, instead of connecting to the upstream and downstream ports  74 ,  76 , the branch conduits  84 ,  86  may connect directly to the upstream and downstream sections of the orifice plate  68 . In such embodiments, the upstream port  74  and the branch conduit  84  may be coupled to the upstream section such that both the upstream pressure sensor  80  and the secondary pressure sensor  90  are exposed to substantially the same fuel pressure. Similarly, the downstream port  76  and the branch conduit  86  may be coupled to the downstream section such that both the downstream pressure sensor  82  and the secondary pressure sensor  92  are exposed to substantially the same fuel pressure. In some embodiments, one or both of the secondary pressure sensors  90 ,  92  may be a differential pressure sensor. In embodiments where secondary pressure sensor  90  is a differential pressure sensor, a branch conduit  88  may fluidly couple branch conduit  86  to secondary pressure sensor  90 . In some embodiments, in addition to secondary pressure sensors  90 ,  92 , other secondary sensors  98  may also be provided for redundant measurement capability of other parameters of the fuel flowing through fuel valve  62 . 
         [0018]    The signals from the secondary pressure sensors  90 ,  92  may be directed to control system  60 . The control system  60  may use these received signals to determine the flow rate of fuel through fuel valve  62 , independent of the flow rate communicated to the control system  60  by electronics module  72 . The ability of the control system  60  to independently measure the flow rate enables the flow rate to be measured accurately even when the sensors of the electronic module  72  are non operational or faulty. Thus the secondary pressure sensors  90 ,  92  provide redundant flow measurement capabilities to fuel valve  62 . If the control system  60  detects a difference in the determined and the received values of flow rate (referred to herein as “error”), the control system  60  may take corrective action. 
         [0019]    The corrective action taken by the control system  60  may depend upon the application. For instance, in some embodiments, the control system  60  may shut down the gas turbine engine  100  if the error exceeds a threshold value. In some embodiments, the control system  60  may alert an operator (for example, using an alarm  94  and/or an indicator light  96 ) in response to an error exceeding a threshold value. In embodiments using a dual fuel gas turbine engine  100 , the control system  60  may switch the fuel supply to the gas turbine engine  100  in response to an error in fuel flow measurement. For instance, if an error exceeding a threshold value in the flow rate of gaseous fuel is detected, the control system  60  may turn off the supply of gaseous fuel to the turbine engine  100  and operate the turbine engine  100  using liquid fuel until the error is fixed. It should be noted that the corrective actions described above are only exemplary, and in general, any type of corrective action may be carried out by the control system  60  in response to a detected error. 
         [0020]    In some embodiments, the liquid fuel supply to the gas turbine engine  100  may also be provided with redundant flow measurement capability in a manner described above. It should be noted that although a dual fuel gas turbine engine  100  is described herein, this is only exemplary. That is, in some embodiments, gas turbine engine  100  may be a single fuel gas turbine engine. It should further be noted that, although the novel aspects of the current disclosure are described with reference to a gas turbine engine, this is only exemplary. In general, the disclosed flow control system may be applied to any application. For instance, the flow control system of the current disclosure may be applied to control the fuel flow to another engine, such as, for example, an internal combustion engine, or to measure the flow of a fluid through a pipeline. 
       INDUSTRIAL APPLICABILITY 
       [0021]    The disclosed fuel valve may be applicable to any gas turbine engine in which reliable fuel flow is desired. The disclosed fuel valve may be used to provide redundant fuel flow measurement capability to any gas turbine engine regardless of the type of fuels used. The operation of gas turbine engine  100  will now be explained. 
         [0022]      FIG. 4  is a flow chart that illustrates an exemplary operation of the gas turbine engine  100 . In the exemplary application, the gas turbine engine  100  is operated using a gaseous fuel directed thereto, through gaseous fuel pipe  22  (step  110 ). As the gaseous fuel flows through the gaseous fuel pipe  22 , the fuel valve  62  measures the quantity of fuel (such as, mass flow rate) passing through the gaseous fuel pipe  22  (step  120 ). The value of the measured quantity of fuel is communicated from the fuel valve  62  to the control system  60  (step  130 ). The control system  60  also determines the quantity of fuel passing through the gaseous fuel pipe  22  independently of the value measured by the fuel valve  62 , using pressure data from the secondary pressure sensors  90  and  92  (step  140 ). The control system  60  then determines the difference between the measured and the determined values of the quantity of fuel directed to the gas turbine engine  100  (step  150 ). If the difference between these values is greater than or equal to a threshold (step  160 ), the control system  60  takes corrective action (step  170 ). If the difference between the received and computed values is less than the threshold, the control system continues to monitor the flow through the fuel valve  62 . Incorporating a redundant fuel flow measurement capability to the fuel valve  62  allows the fuel flow to turbine engine  100  to be measured in a reliable manner even when the flow meter is non operational or faulty. 
         [0023]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed fuel valve. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed fuel valve. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.