Patent Publication Number: US-8534041-B2

Title: Apparatus and assembly for a spark igniter having tangential embedded pins

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention relates generally to spark igniters, and more specifically, to an apparatus and assembly for an extended life igniter assembly. 
     At least some known gas turbine engines include a spark igniter to facilitate engine starting and/or running. Such igniters are typically surface gap spark plugs in which a high energy spark discharge occurs between a center electrode and a ground electrode, traveling along the surface of an insulator. The spark discharge in such igniters is of the “high energy type” because of the nature of the ignition system used to cause sparking. The system includes a storage capacitor which is charged as the voltage applied thereto and across the igniter increases; when the applied voltage becomes sufficiently large to cause a spark discharge the electrical energy stored by the capacitor is discharged, flowing across the spark gap. 
     Electrode erosion has been a problem with spark igniters used with turbine engines for jet aircraft, sometimes constituting the limiting condition with respect to igniter life. Problem erosion of both the center electrode and the ground shell electrode occurs in igniters used with turbine engines. Conventional igniter ground electrodes are frequently made from Inconel® or from other conventional nickel alloys because they are relatively inexpensive. However, such electrodes may not provide the required service life in certain environments and duty cycles. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, an igniter includes a shell comprising a base, a tip insulator surface, and a sidewall extending therebetween wherein the sidewall surrounds a cavity within the shell. The igniter also includes a shell bore extending from the tip surface to the cavity and a pin embedded into the tip surface extending substantially tangentially with respect to the bore. 
     In another embodiment, an igniter assembly includes a substantially cylindrical shell including a base, a tip surface, and a sidewall extending therebetween, the sidewall surrounding a cavity within the shell, the shell having a longitudinal axis extending parallel to the sidewall and orthogonally with respect to the tip surface. The igniter assembly also includes a shell bore extending from the tip surface to the cavity, the shell bore concentric with the longitudinal axis, at least one erosion-resistant pin coupled to the tip surface in a substantially tangential orientation with respect to the bore, and an electrode positioned within the shell, the electrode including a distal firing end positioned proximate the bore. 
     In yet another embodiment, a gas turbine engine includes a combustor including a sidewall enclosing a combustion chamber and an igniter assembly extending at least partially through the sidewall such that a tip of the igniter assembly is in flow communication with the combustion chamber, the igniter assembly including a tip surface including a shell bore and at least one erosion-resistant pin coupled to the tip surface in a substantially tangential orientation with respect to the bore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-5  show exemplary embodiments of the apparatus and assembly described herein. 
         FIG. 1  is a schematic illustration of a gas turbine engine assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a perspective view, partially cut away of an igniter assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  is a perspective end view of igniter assembly in accordance with another embodiment of the present invention; 
         FIG. 4  is an end view of igniter assembly in accordance with an embodiment of the present invention; and 
         FIG. 5  is a side view of igniter assembly in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description illustrates embodiments of the invention by way of example and not by way of limitation. It is contemplated that the invention has general application to providing reliable operation and extended igniter component life in industrial, commercial, and residential gas turbine applications. 
     As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
       FIG. 1  is a schematic illustration of a gas turbine engine assembly  8  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, gas turbine engine assembly  8  includes a high bypass, turbofan gas turbine engine  10  having in serial flow communication an inlet  12  for receiving ambient air  14 , a fan  16 , a compressor  18 , a combustor  20 , a high pressure turbine  22 , and a low pressure turbine  24 . High pressure turbine  22  is coupled to compressor  18  using a first shaft  26 , and low pressure turbine  24  is coupled to fan  16  using a second shaft  28 . Gas turbine engine  10  has an axis of symmetry  32  extending from an upstream side  34  of gas turbine engine  10  aft to a downstream side  36  of gas turbine engine  10 . In the exemplary embodiment, gas turbine engine  10  also includes at least one igniter assembly  40  that is coupled proximate to combustor  20 . Gas turbine engine  10  also includes at least one spark detector  42  and at least one pressure transducer  44  that are each coupled to gas turbine engine  10 . In the exemplary embodiment, spark detector  42  is configured to detect a spark that is generated by igniter assembly  40 , and pressure transducer  44  is configured to determine a pressure within combustor  20  approximately adjacent to spark igniter assembly  40 . 
     During operation, airflow enters gas turbine engine  10  through inlet  12  and is compressed utilizing compressor  18 . The compressed air is channeled downstream at an increased pressure and temperature to combustor  20 . Fuel is introduced into combustor  20  wherein the air and fuel are mixed and ignited within combustor  20  to generate hot combustion gases. Specifically, pressurized air from compressor  18  is mixed with fuel in combustor  20  and ignited utilizing igniter assembly  40 , thereby generating combustion gases. Such combustion gases are then utilized to drive high pressure turbine  22  which drives compressor  18  and to drive low pressure turbine  24  which drives fan  16 . 
       FIG. 2  is a perspective view, partially cut away of an igniter assembly  40  in accordance with an exemplary embodiment of the present invention. In the exemplary embodiment, igniter assembly  40  includes a shell  200  including a base (not shown in  FIG. 2 ), a tip surface  202 , and a sidewall  204  extending therebetween. Sidewall  204  surrounds a cavity  206  within shell  200 . Shell  200  includes a shell bore  208  extending from tip surface  202  to cavity  206 . In the exemplary embodiment, a pin  210  is embedded into tip surface  202  and extends substantially tangentially with respect to shell bore  208 . In various embodiments, pin  210  includes an at least one of a circular cross-section, a partially circular cross-section, a polygonal cross-section, and an arcuate cross-section. Pin  210  may be coupled to tip surface  202  using a braze joint, a weld joint, a friction fit, an interference fit, or a combination thereof. Moreover, in another embodiment, pin  210  includes a width  209  and tip surface  202  includes a slot  211  having an opening  213  in tip surface  202 . Slot  211  is configured to receive pin  210 , wherein width  209  of slot opening  213  is less than width  209  of pin  210  providing an interference fit for pin  210 . In various embodiments, tip surface  202  includes a plurality of pins, at least one of which is oriented tangentially with respect to shell bore  208 . Also, in various embodiments, slot  211  may be at least partially open to shell bore  208 . Pins  210  are intended to increase a life of igniter assembly  40  by being resistant to erosion of tip surface  202 . In the exemplary embodiment, pins  210  comprise Iridium (Ir), Tungsten (W), Platinum (Pt), Rhodium (Rh), Ruthenium (Ru), Osmium (Os), or an alloy thereof. 
     Igniter assembly  40  further includes an electrode  212  positioned within shell  200 . In the exemplary embodiment, electrode  212  includes a distal firing end  214  positioned proximate shell bore  208  and spaced apart from tip surface  202  by a spark gap  215 . 
     An insulator  216  is positioned within shell  200  between shell  200  and electrode  212 . Insulator  216  includes an insulator bore in substantial axial alignment with shell bore  208 . In the exemplary embodiment, shell  200 , insulator  216 , and electrode  212  are substantially concentrically aligned with shell bore  208  and insulator bore  218 . In various embodiments, shell  200 , insulator  216 , electrode  212 , shell bore  208 , and insulator bore  218  are aligned differently with respect to each other. 
       FIG. 3  is a perspective end view of igniter assembly  40  in accordance with another embodiment of the present invention. In this embodiment, three pins  210  are used in an orientation wherein all three pins  210  are aligned substantially tangentially with respect to shell bore  208 . 
       FIG. 4  is an end view of igniter assembly  40  in accordance with an embodiment of the present invention. In the exemplary embodiment, igniter assembly  40  includes a rectangular or square cross-section  400  that may be machined to a circular cross-section  402  during fabrication. Four pins  210  are embedded in tip surface  202  and circumscribe shell bore  208  tangentially. 
       FIG. 5  is a side view of igniter assembly  40  in accordance with an embodiment of the present invention. 
     The above-described embodiments of an apparatus and assembly for a spark igniter provide a cost-effective and reliable means for extending a life of engine ignition components. More specifically, the apparatus and assembly described herein facilitate reducing wear of igniter components during use. As a result, the apparatus and assembly described herein facilitate increasing time between maintenance activities in a cost-effective and reliable manner. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.