Abstract:
A gas turbine engine comprising a combustor having a combustor liner assembly and a mounting bracket provided on the combustor liner assembly, a floating collar being slidingly received on the mounting bracket for relative sliding movement in a plane normal to an axis of an igniter opening in the liner assembly. The floating collar includes an annular surface defining a collar opening, and an igniter having an axis concentric with the axis of the collar opening is sealingly engages the annular surface. A plurality of purge openings defined in at least one of the igniter and the floating collar form cooling airflow passages communicating from the plenum to the cavity.

Description:
TECHNICAL FIELD 
       [0001]    The described subject matter relates generally to gas turbine engines and, more particularly, to an igniter assembly for a combustor. 
       BACKGROUND 
       [0002]    In a gas turbine engine, the interaction between the fuel nozzle spray and the spark from the igniter can affect the stability of the combustion process and the altitude re-ignition capability of the combustion system. The igniter tip has to be close enough to the fuel spray to spark the ignition, yet it cannot be too exposed so that it can be burnt and rendered less effective. In existing combustor designs, the igniter is typically buried in a cavity with the igniter tip barely exposed to the hot gas path. As the igniter should not take any mechanical load during the entire flight envelope, there is usually a gap provided between the igniter and the igniter cavity wall to prevent any transient or steady-state interference of the igniter and the cavity wall. However this gap can allow hot gas ingestion into the cavity and eventually burn the igniter and the surrounding panel or combustor liner. 
       SUMMARY 
       [0003]    There is provided a gas turbine engine comprising: a combustor having a combustor liner assembly defining a domed combustion chamber in a plenum of the gas turbine engine, a plurality of fuel nozzles communicating through a dome of the combustor, and an igniter opening defined in the combustor liner assembly downstream from the fuel nozzles relative to a direction of air flow through the combustion chamber; a mounting bracket provided on the combustor liner assembly and including an annular lip at least partially aligned with the igniter opening such as to define a cavity receiving an igniter therein; a floating collar slidingly received on the mounting bracket for relative sliding movement in a plane normal to an axis of the igniter opening, the floating collar including an annular surface defining a collar opening; the igniter having an axis concentric with said axis of the collar opening and sealingly engaging the annular surface ; and a plurality of purge openings defined in at least one of the igniter and the floating collar, the purge openings forming cooling airflow passages communicating from the plenum to the cavity. 
         [0004]    There is also provided a method of minimizing damage to the tip of an igniter in a combustor of a gas turbine engine, the method comprising the steps of: mounting the igniter to a liner of the combustor downstream of one or more fuel nozzles using a floating collar; providing an annular cavity surrounding the igniter tip; forming a plurality of purge openings in at least one of the igniter and the floating collar, the purge openings defining cooling airflow; and directing pressurized air from a plenum surrounding the combustor through the purge openings and into the cavity, the purge openings thereby creating cooling purge air jets. 
         [0005]    Further details of these and other aspects will be apparent from the detailed description and figures included below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Reference is now made to the accompanying figures in which: 
           [0007]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine illustrating the turbofan configuration; 
           [0008]      FIG. 2  is a partly fragmented axial cross-sectional view showing a combustor having an igniter assembly in accordance with one embodiment of the present disclosure; 
           [0009]      FIG. 3  is a fragmentary, perspective, cross-sectional view showing a detail in accordance with an embodiment of the present disclosure; 
           [0010]      FIG. 4   a  is a fragmentary, schematic, enlarged view of a detail in accordance with the embodiment shown in  FIG. 3 ; 
           [0011]      FIG. 4   b  is a fragmentary, schematic, enlarged view of a detail similar to  FIG. 4   a , but in accordance with another embodiment; 
           [0012]      FIG. 5  is a fragmentary, perspective, cross-sectional view showing a detail in accordance with still another embodiment of the present disclosure; 
           [0013]      FIG. 6  is a fragmentary, perspective, cross-sectional view showing a detail in accordance with yet another embodiment of the present disclosure; 
           [0014]      FIG. 7  is a fragmentary, perspective, cross-sectional view showing a detail in accordance with a further embodiment of the present disclosure; 
           [0015]      FIG. 7   a  is a fragmentary, enlarged, schematic view of a detail in  FIG. 7  according to one version of the embodiment therein; and 
           [0016]      FIG. 7   b  is a fragmentary, enlarged, schematic view of a detail in  FIG. 7  according to another version of the embodiment therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication: a fan  12  through which ambient air is propelled; a compressor section  14  for pressurizing the air; a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases; and, a turbine section  18  for extracting energy from the combustion gases. The fan  12 , compressor section  14 , combustor  17  and turbine  18  are all positioned concentrically about a common central longitudinal axis  11  of the gas turbine engine  10 . 
         [0018]    Referring to  FIG. 2 , the combustor  16  is housed within a plenum  17  that is defined and enclosed by a case  19  of the gas generator portion of the engine. The plenum  17  is supplied with compressed air from the compressor  14  located upstream of the combustor and gas generator portion. The combustor  16  comprises an annular combustor shell  20 , typically composed of a radially inner liner  20   a  and a radially outer liner  20   b,  each having a wall  30 ,  32  respectively, defining a combustion chamber  22  within the combustor  16 . A dome panel  23  is provided at the upstream end of the combustor  16 . A plurality of circumferentially spaced-apart fuel nozzles  24  are mounted in the dome panel  23  for delivering a fuel-air mixture into the combustion chamber  22 . 
         [0019]    A plurality of circumferentially spaced-apart openings  34  are provided in at least the outer liner  20   b  of the combustor  16 . An igniter assembly  25  is mounted on the liner  20   b,  at each opening  34 , for igniting the fuel air mixture delivered by the fuel nozzles  24  in the chamber  22 . The igniter assembly  25  includes at least an igniter  26  and a floating collar  28 . The floating collar  28  is held to the combustor liner  20   b  by a mounting bracket  36  fixedly attached to the liner  20   b.  As shown in  FIG. 3  and  FIG. 5 , the mounting bracket  36  is provided on the combustor liner  20   b  and includes an annular lip  37  which is at least partially aligned within the opening  34  so as to define a cavity  35 , circumscribed by the opening  34  and the lip  37 , for receiving a tip  27  of the igniter  26 . The floating collar  28  slides laterally on an interface surface  29  formed on the mounting bracket  36 , and therefore the floating collar is able to slide relative to the mounting bracket in a plane normal to the axis of the igniter opening  34 . The collar  28  also includes an annular surface  46  defining a collar opening in which the igniter  26  is mounted. The interface between the annular surface  46  and the igniter  26  may be less than 0.010″ in radius, or within sealing tolerances. The floating collar  28  is therefore mounted between the combustor liner  20   b  and the igniter  26  to provide a seal therebetween, while allowing the igniter  26  to move relative to the combustor liner  20   b . The floating collar  28  and the collar mounting bracket  36  may be advantageously fabricated by metal injection moldings (MIM), although other methods of manufacture may be used to form the floating collar  28  and mounting bracket  36 . The purge bores and slots, to be described, may be formed without resorting to more expensive machining processes. 
         [0020]    In order to prevent the hot gases in the dome region of the combustor chamber  22  from damaging the tip  27  of the igniter  26 , cool air, designated here as purge air, coming from the pressurized plenum  17  is directed to the igniter cavity  35  surrounding the igniter tip  27 . As shown in  FIGS. 3 and 4   a , the purge air flow can flow from the plenum  17  to the cavity  35  by means of a plurality of purge slots  38   a  defined axially on the circumference of the sheath of the igniter  26 . These purge slots may also be impingement slots, in that they may be used be used to direct purge and/or inpingement airflow therethrough. The purge slots  38   a  would preferably be provided on the upstream side of the igniter  26  in a sector not exceeding an arc of 120°. In one specific example, which is exemplary only, seven purge slots  38   a  are provided within an arc of 90°. 
         [0021]    As an option to the configuration shown in  FIGS. 3 and 4   a , the purge slots  38   b  may be alternately provided in the annular surface  46  of the floating collar  28 , as shown in  FIG. 4   b . In both cases, however, the purge slots  38   a  and  38   b  extend axially relative to the igniter  26  such as to provide cooling air flow between the igniter  26  and the surrounding floating collar  28 . 
         [0022]    It is also to be understood that the purge air slots as described herein, which are used to direct cooling purge air into the cavity  35  proximate the tip  27  of the igniter  26 , may comprise bores or slots having a number of cross-sectional profiles, such as circular, semi-circular, rectangular, etc. Regardless, they extend through at least one of the floating collar and the igniter wall surface such as to ensure fully uninterrupted cooling air flow paths in each of the passages formed by these slots and therefore provide cooling airflow communication between the cavity  35  of the igniter tip  27  and the plenum  17  surrounding the combustor  16 . 
         [0023]    According to the alternate embodiment shown in  FIG. 5 , the purge air flow may be introduced to the cavity  35  through a plurality of discrete purge bores  40  provided in the collar  28 . The purge bores  40  are provided on the upstream side of the igniter assembly. These bores  40  may be axial and therefore parallel to the axis of the igniter  26 . The purge bores  40  direct the purge air flow to the cavity  35  formed in the mounting bracket  36  surrounding the igniter tip  27 . In one example, 7 slots were provided in a sector contained by a 90° arc. The sector could be up to an arc of 120° with anywhere from 10 to 20 purge bores  40 . It has also been contemplated to angle the purge bores  40  to between 30° and 55° with the axis of the igniter  26 . The selection of the angle and number of purge bores  40  depends on the amount of purge air available and the area that needs to be protected. 
         [0024]    The embodiment shown in  FIG. 6  shows purge bores  42  defined in the mounting bracket  36 . The radial bores  42  are directed to the cavity  35 , in order to deliver the flow of purge air to this area. A cluster of  10  to  20  purge bores  42  were arranged in a sector covering an arc of 120°, on the upstream side of the igniter  26 . 
         [0025]      FIGS. 7 ,  7   a ,  7   b  illustrate radial purge slots  44  formed between the mounting bracket  36  and the floating collar  28  at the sealing interface  46  between the two parts. As shown in  FIG. 7   a , the purge slots  44   a  are formed in the floating collar  28 . Alternatively, the purge slots  44   b  are provided in the mounting bracket  36  at the interface  46 . 
         [0026]    The purge bores  42  or the purge slots  44  could be arranged at an angle tangential to the periphery of the cavity  35 . This would allow the purge air flow area to cover a larger area. 
         [0027]    The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the described subject matter. For example, the purge openings may be the form of slots defined in one of the igniter and the annular surface of the floating collar at the interface thereof, coaxial with the axis of the opening, for providing the flow of purge air. In another embodiment, the purge openings may be the form of purge bores in the floating collar for passing the flow of purge air from the plenum to the cavity. In all cases the full combustor ΔP causes the purge air flow through the purge openings, which create cooling purge air flow jets through the igniter assembly such as to cool the igniter tip. Modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.