Turbine engine having acoustically tuned fuel nozzle

Abstract

A fuel nozzle for a turbine engine having a combustion chamber is disclosed. The fuel nozzle has a common axis, a body member, and a barrel member. The fuel nozzle also has a mixing duct and an air inlet duct, each with predetermined lengths. The fuel nozzle additionally has a main fuel injection device located between the air inlet duct and the mixing duct. The main fuel injection device is configured to introduce a flow of fuel into the barrel member at a predetermine axial fuel introduction location. The predetermined axial fuel introduction location and the predetermined length of at least one of the mixing duct and the air inlet duct are such that a time-varying fuel to air equivalence ratio at a flame front downstream of an exit of the mixing duct is less than a time-averaged fuel to air equivalence ratio when a naturally-occurring time-varying pressure at the flame front is at a maximum.

1 . A fuel nozzle for a turbine engine having a combustion chamber, comprising: 
 a common axis;    a body member disposed about the common axis;    a barrel member located radially outward from the body member;    a mixing duct fluidly communicating the barrel member and the combustion chamber, and having a predetermined length;    an air inlet duct disposed upstream of the barrel member, having a predetermined length, and being configured to introduce a flow of air into the barrel member; and    a main fuel injection device located between the air inlet duct and the mixing duct, the main fuel injection device configured to introduce a flow of fuel into the barrel member at a predetermine axial fuel introduction location,    wherein the predetermined axial fuel introduction location and the predetermined length of at least one of the mixing duct and the air inlet duct are such that a time-varying fuel to air equivalence ratio at a flame front downstream of an exit of the mixing duct is less than a time-averaged fuel to air equivalence ratio when a naturally-occurring time-varying pressure at the flame front is at a maximum.    
   
   
       2 . The fuel nozzle of  claim 1 , wherein the predetermined axial fuel introduction location and the predetermined length of the at least one of the mixing duct and the air inlet duct are also such that the time-varying fuel to air equivalence ratio at the flame front is greater than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at a minimum.  
   
   
       3 . The fuel nozzle of  claim 2 , wherein the predetermined lengths of both the mixing duct and air inlet duct are set such that the time-varying fuel to air equivalence ratio is greater than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at the minimum and less than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at the maximum.  
   
   
       4 . The fuel nozzle of  claim 1 , wherein the flow of air introduced to the barrel member is a time-varying flow and the fuel nozzle further includes at least one air injection port configured to inject compressed air into the barrel member at a predetermined axial location approximately 180 degrees out of phase with the time-varying flow of air such that attenuation of a pressure wave traveling from the air inlet duct toward the mixing duct occurs.  
   
   
       5 . The fuel nozzle of  claim 4 , wherein the at least one air injection port is a first air injection port and the fuel nozzle further includes at least a second air injection port axially aligned with the first air injection port.  
   
   
       6 . The fuel nozzle of  claim 4 , wherein the air inlet duct introduces a greater amount of air into the fuel nozzle than the at least one air injection port.  
   
   
       7 . The fuel nozzle of  claim 4 , further including a flow restrictor located proximal the air inlet duct, the flow restrictor configured to divert a predetermined portion of the compressed air from the air inlet duct toward the at least one air injection port.  
   
   
       8 . The fuel nozzle of  claim 1 , wherein the air inlet duct is substantially straight.  
   
   
       9 . The fuel nozzle of  claim 1 , wherein the mixing duct is substantially straight.  
   
   
       10 . The fuel nozzle of  claim 1 , wherein the length of the inlet air duct is such that an axial location of the introduction of the flow of air is substantially coterminous with the predetermined axial fuel introduction location.  
   
   
       11 . A method of operating a turbine engine, the method comprising: 
 directing compressed air into the turbine engine via an inlet duct having a predetermined length;    introducing fuel into the turbine engine at a predetermined axial position downstream of the inlet duct;    mixing the fuel and air within a mixing duct having a predetermined length; and    directing the fuel and air mixture to a combustion chamber,    wherein the predetermined axial fuel introduction location and the predetermined length of at least one of the mixing duct and the inlet duct are such that a time-varying fuel to air equivalence ratio at a flame front downstream of an exit of the mixing duct is less than a time-averaged fuel to air equivalence ratio when a naturally-occurring time-varying pressure at the flame front is at a maximum.    
   
   
       12 . The method of  claim 11 , wherein the predetermined axial fuel introduction location and the predetermined length of at the least one of the mixing duct and the inlet duct are also such that the time-varying fuel to air equivalence ratio at the flame front is greater than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at a minimum.  
   
   
       13 . The method of  claim 11 , wherein the predetermined lengths of both the mixing duct and inlet duct are set such that the time-varying fuel to air equivalence ratio is greater than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at the minimum and less than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at the maximum.  
   
   
       14 . The method of  claim 11 , wherein the air directed in to the turbine engine has a time-varying flow characteristic and the method further includes injecting compressed air into the turbine engine at a predetermined axial location approximately 180 degrees out of phase with the time-varying flow of air such that attenuation occurs.  
   
   
       15 . The method of  claim 14 , wherein the flow rate of compressed air through the inlet duct is greater than the flow rate of air injected at the predetermined axial location within the turbine engine.  
   
   
       16 . The method of  claim 11 , further including diverting compressed air from upstream of the inlet duct around the inlet duct to an injection location downstream of the inlet duct.  
   
   
       17 . A turbine engine, comprising: 
 a compressor section configured to pressurize inlet air;    a combustion chamber configured to receive the pressurized air; and    a fuel nozzle configured to direct fuel into the combustion chamber, the fuel nozzle having: 
 a common axis;  
 a body member disposed about the common axis;  
 a barrel member located radially outward from the body member;  
 a mixing duct fluidly communicating the barrel member and the combustion chamber, and having a predetermined length;  
 an air inlet duct disposed upstream of the barrel member, having a predetermined length, and being configured to introduce a flow of air into the barrel member; and  
 a main fuel injection device located between the air inlet duct and the mixing duct, the main fuel injection device configured to introduce a flow of fuel into the barrel member at a predetermine axial fuel introduction location,  
 wherein the predetermined axial fuel introduction location and the predetermined lengths of the mixing duct and the air inlet duct are such that a time-varying fuel to air equivalence ratio is greater than a time-averaged fuel to air equivalence ratio when a time-varying pressure at a flame front downstream of an exit of the mixing duct is at a minimum and less than the time-averaged fuel to air equivalence ratio when the time-varying pressure at the flame front is at a maximum.  
   
   
   
       18 . The turbine engine of  claim 17 , wherein the flow of air introduced to the barrel member is a time-varying flow and the fuel nozzle further includes a plurality of axially aligned air injection ports configured to inject compressed air into the barrel member at a predetermined axial location approximately 180 degrees out of phase with the time-varying flow of air such that attenuation of a pressure wave traveling from the air inlet duct toward the mixing duct occurs.  
   
   
       19 . The turbine engine of  claim 17 , wherein the air inlet duct introduces a greater amount of air into the fuel nozzle than the at least one air injection port.  
   
   
       20 . The turbine engine of  claim 17 , further including a flow restrictor located proximal the air inlet duct, the flow restrictor configured to divert a predetermined portion of the compressed air from the air inlet duct toward the at least one air injection port.  
   
   
       21 . The turbine engine of  claim 17 , wherein the air inlet and mixing ducts are both substantially straight.