Passive purge injectors

Abstract

A method of injecting fuel in a gas turbine engine includes injecting gaseous fuel from a gaseous fuel circuit of an injector in a first mode, wherein flow of gaseous fuel from the gaseous fuel circuit constricts air flow from an air circuit. The method includes injecting liquid fuel from a liquid fuel circuit in a second mode, idling flow in the gaseous fuel circuit and flowing air through the air circuit for passive purge to prevent liquid fuel from migrating into the gaseous fuel circuit. The method includes injecting a gaseous fuel that lies within a range of different Wobbe Index values, wherein regardless of where the gaseous fuel falls in the range, it does not prevent operation in the first and second modes as described above.

What is claimed is: 
     
         1 . A method of injecting fuel in a gas turbine engine comprising:
 injecting gaseous fuel from a gaseous fuel circuit of an injector in a first mode, wherein flow of gaseous fuel from the gaseous fuel circuit constricts air flow from an air circuit outboard or inboard of the gaseous fuel circuit in the first mode;   injecting liquid fuel from a liquid fuel circuit in a second mode, wherein the second mode includes idling flow in the gaseous fuel circuit and flowing air through the air circuit for passive purge to prevent liquid fuel from migrating into the gaseous fuel circuit, wherein switching the air circuit between constricted flow in the first mode and unconstricted flow in the second mode is accomplished by activating or idling the gaseous fuel circuit, respectively; and   wherein injecting gaseous fuel includes injecting a gaseous fuel that lies within a range of different Wobbe Index values ranging from a first Wobbe Index value to a second Wobbe Index value, and wherein, wherein regardless of where the gaseous fuel falls in the range of different Wobbe Index values, it does not prevent operation in the first mode constricting air flow from the air circuit in the first mode, and wherein regardless of where the gaseous fuel falls in the range of different Wobbe Index values, it does not prevent operation in the second mode preventing liquid fuel migrating into the gas circuit in the second mode.   
     
     
         2 . The method as recited in  claim 1 , wherein the first Wobbe Index value and the second Wobbe Index value differ by a factor up to 3. 
     
     
         3 . The method as recited in  claim 1 , wherein the first Wobbe Index value and the second Wobbe Index value differ by a factor of 3 or more. 
     
     
         4 . The method as recited in  claim 1 , wherein constricting air flow from the air circuit in the first mode includes flowing gaseous fuel from the gaseous fuel circuit in a flow path that crosses an outlet opening of the air circuit, restricting how much air can flow through the air circuit. 
     
     
         5 . The method as recited in  claim 4 , wherein flowing gaseous fuel in a flow path that crosses the outlet opening of the air circuit includes flowing the gaseous fuel from a converging lip bounding an outlet of the gaseous fuel circuit to a converging lip bounding the outlet opening of the air circuit. 
     
     
         6 . The method as recited in  claim 5 , wherein the converging lip bounding the outlet of the gaseous fuel circuit imparts a momentum vector on gas flowing out of the gaseous fuel circuit to at least partially block off the outlet opening of the air circuit. 
     
     
         7 . The method as recited in  claim 1 , wherein flowing air through the air circuit for passive purge includes impinging air from the air circuit onto an outer surface of a liquid injector inboard of the gaseous fuel circuit. 
     
     
         8 . The method as recited in  claim 7 , wherein impinging air from the air circuit onto the outer surface of the liquid injector includes issuing air from an outlet opening of the air circuit defined between two converging lips of the injector. 
     
     
         9 . The method as recited in  claim 1 , wherein, at least one of back-flowing liquid fuel into a compressor discharge cavity supplying air to the air circuit, migrating liquid fuel into the gaseous fuel circuit, or growing carbon on a conical surface of a liquid injector inboard of the gaseous flow circuit is prevented in the second mode. 
     
     
         10 . The method as recited in  claim 1 , wherein, back-flowing gaseous fuel into a compressor discharge cavity supplying air to the air circuit is prevented in the first mode. 
     
     
         11 . The method as recited in  claim 1 , wherein in the first mode some air is discharged through the constricted air circuit, and wherein gaseous fuel from the gaseous fuel circuit and air from the air circuit both exit the injector through a common exit passage. 
     
     
         12 . The method as recited in  claim 1 , wherein constricting air flow from the air circuit in the first mode includes constricting up to 65% of the air flow through the air circuit compared to air flow through the air circuit in the second mode. 
     
     
         13 . The method as recited in  claim 1 , wherein passive purge to prevent liquid fuel from migrating into the gaseous fuel circuit includes scrubbing liquid fuel from a conical surface of a liquid injector inboard of the gaseous flow circuit with impinging air flow from the air circuit. 
     
     
         14 . A fuel injecting arrangement comprising:
 a body comprising:
 at least one liquid fuel circuit having at least one liquid fuel outlet; 
 at least one air flow circuit having at least one air outlet positioned radially of the liquid fuel outlet; and 
 a gaseous fuel circuit having a gaseous fuel outlet positioned radially of the at least one liquid fuel outlet and radially of the at least one air outlet, 
 the fuel injecting arrangement being configured such that the air flow is constricted from flowing out the at least one air outlet that is immediately radially adjacent to the gaseous fuel outlet when gaseous fuel is flowing out from the gaseous fuel outlet, while also preventing back flow of gaseous fuel into the at least one air outlet that is immediately radially adjacent to the gaseous fuel outlet for a Wobbe Index ranging from a nominal value to a value that is ⅓ to ¼ of the nominal value, 
 the fuel injecting arrangement further being configured such that when liquid fuel is flowing out from the at least one liquid fuel outlet and the gaseous fuel circuit is idle, air flowing from the at least one air outlet that is immediately radially adjacent to the gaseous fuel outlet prevents liquid from settling on the gaseous fuel outlet or back flowing into the gaseous flow circuit through the gaseous fuel outlet. 
   
     
     
         15 . The fuel injector as recited in  claim 14 , wherein a converging lip bounds an outlet of the gaseous fuel circuit forming a conical shape, wherein the converging lip is configured to impart a momentum vector on gas flowing out of the gaseous fuel circuit to at least partially block off the outlet opening of the air circuit in the first mode, such that gaseous fuel flowing through the gaseous fuel circuit is directed at least partially radially inwardly prior to being mixed with air. 
     
     
         16 . A fuel injecting arrangement comprising:
 a body comprising:
 at least one liquid fuel circuit having at least one liquid fuel outlet; 
 at least one air flow circuit having at least one air outlet positioned radially outward of the liquid fuel outlet; and 
 a gaseous fuel circuit having a gaseous fuel outlet positioned radially between the at least one liquid fuel outlet the at least one air outlet, the gaseous fuel outlet having a frustoconical shape such that gaseous fuel flowing out from the gaseous fuel outlet is directed partially radially inwardly prior to being mixed with air.