Abstract:
A combustor assembly includes a combustor chamber having a primary and intermediate zone that provides for reduced flame temperatures. The combustor assembly includes first and second pluralities of injectors. The first plurality of injectors introduces fuel to a primary zone. A second plurality of injectors introduces fuel to an intermediate zone. During operation between initial start up and before the introduction of engine load, fuel is introduced into the primary zone only by the first plurality of injectors. Once engine load is applied to the engine, fuel is introduced into the intermediate zone by the second plurality of injectors. Introduction of additional volume of fuel allows the fuel-air ratio to remain constant regardless of engine operating conditions. The constant fuel-air ratio is maintained at a desired rate to lower flame temperatures and reduce nitrous oxide emissions.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to a combustor and specifically to a combustor including features reducing nitrous oxide (NO x ) emissions. 
   Conventional gas turbine engines include a combustor for mixing and burning a fuel air mixture to produce an exhaust gas stream that turns a turbine. Conventional combustors operate near stoichiometric conditions in the primary zone. Such conditions produce higher than desired combustor temperatures. The high combustor temperatures produce greater than desired amounts of nitrous oxide. Environmental concerns and regulation have created the demand for gas turbine engines with reduced nitrous oxide emissions. 
   Current combustors utilize many different configurations to optimize burning of fuel within the combustor. Many of these configurations include devices for initiating swirl of the fuel and air mixture within the combustor. Such devices improve the efficiency of fuel burning within the combustor. However, each of these devices requires a compromise of the two desirable conditions. That is, during the starting condition the fuel-air ratio is not exactly as would otherwise be desired because of the performance requirements required of the gas turbine engine under full load conditions. As appreciated, the compromise between optimal starting conditions and optimal engine operating conditions results in sacrifices being made for each engine operating condition. 
   Accordingly, it is desirable to develop a combustor that operates at a reduced temperature to reduce nitrous oxide emissions while providing desired starting and operating performance. 
   SUMMARY OF THE INVENTION 
   This invention is a combustor that includes first and second plurality of independently operable injectors that introduce fuel to select portions of the combustor. 
   The combustor of this invention includes a reverse-flow annular chamber that includes features that encourage complete fuel-air mixture. The combustion chamber includes a primary zone and an intermediate zone. In the primary zone, fuel and air is introduced through a first plurality of injectors. This first plurality of injectors includes dual orifice injectors that provide fuel-air mixture to the primary zone. During initial start up operations of the gas turbine engine the first plurality of injectors introduces the fuel-air mixture only into the primary zone. An igniter disposed within the primary zone ignites the fuel-air mixture. 
   Fuel is introduced into the intermediate zone of the combustion chamber by a second plurality of injectors. The second plurality of injectors includes an orifice that is directed to introduce fuel into the intermediate zone. The fuel-air mixture introduced into the primary and intermediate zones are essentially the same to provide a consistent lean fuel-air mixture. The additional quantity of fuel-air mixture into the combustor increases the power output of the engine. The additional fuel-air mixture in the intermediate zone at the same fuel-air ratio as is introduced in the primary zone and provides for the increase of power without increasing the fuel-air ratio or temperature within the combustor. 
   Accordingly, the combustor of this invention provides for optimal operation of a gas turbine engine during starting conditions and during engine load operating conditions without an increase in temperature to therefore reduce nitrous oxide emissions. 
   These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a section of the combustor chamber of this invention. 
       FIG. 2  is a cross-sectional view of the annular combustor chamber of this invention. 
       FIG. 3  is a perspective view of the outside of the combustor and fuel injectors. 
       FIG. 4  is a perspective view of the fuel injectors separate from the combustor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , a gas turbine engine assembly  10  includes a combustor  12  that includes a combustor chamber  14 . The combustor chamber  14  includes an interior portion  18  and an outlet portion  20 . Within the interior portion  18  is a primary zone  30 . Adjacent the outlet portion  20  is an intermediate zone  32 . The combustor chamber  14  illustrated is of a reverse annular configuration. A worker with the benefit of this disclosure would understand the application of this invention to combustors of other designs and configurations. 
   The combustor  12  includes a first plurality of injectors  22 . The combustor  12  further includes a second plurality of injectors  24  (Best shown in  FIG. 3 ). Each of the first and second pluralities of injectors  22 ,  24  are disposed in the combustor  12  at a position adjacent both the primary and intermediate zones  30 ,  32 . 
   The combustor  12  also includes a plurality of effusion openings  40  that communicate high-pressure air into the combustor chamber  14 . The effusion openings  40  are illustrated much larger than actual size to illustrate the configuration of the combustor  12 . The effusion openings  40  are small holes with a diameter of approximately 0.020 inches. Each of the effusion openings  40  is angled relative to the combustor chamber  14  to initiate swirling of combustion gases. Swirling of the combustion gases within the combustor chamber  14  provides for more efficient combustion. The swirling of the air and fuel within the combustor chamber  14  initiates optimal combustion and also produces fire swirling. Further, the swirling of the combustion gases produces a favorable and uniform temperature distribution throughout the combustor chamber  14 . The favorable temperature distribution further optimizes combustion of the fuel-air mixture within the combustor. 
   The effusion openings  40  are disposed about the circumference of the combustor chamber  14  and are angled relative to an inner surface  13  of the combustor  12 . Preferably, the effusion openings  40  are disposed at a swirl angle  42  of between 45° and 90°. The angle  42  is shown schematically for clarity and would be arranged transverse to the axis  15  to initiate rotational swirling within the combustor chamber  14 . The effusion openings  40  include a down angle  43  of between 15° and 45° downstream. The angles  42  and  43  are shown schematically for clarity. Other angles for the effusion openings  40  are within the contemplation of this invention to provide desired swirling and mixing for combustors of differing configurations. 
   The first and second pluralities of injectors  22 ,  24  are actuatable independent of each other. An inlet passage  16  communicates fuel and air to the first and second pluralities of injectors  22 ,  24 . The inlet passage  16  is shown schematically and is not necessarily the only configuration that can be utilized with this invention. 
   The fuel-air mixture within the combustor  12  is ignited by a plurality of igniters  26 . The igniters  26  ignite the fuel-air mixture within the combustor chamber  14  to produce gases that exit as indicated at  34 . These gasses exit the combustor  12  to drive a turbine as is know in the art. 
   During initial start up conditions fuel is injected only into the primary zone  30 . In the primary zone  30  the igniter  26  ignites the fuel-air mixture to produce the exhaust gasses  34 . Initial operating conditions include the starting point to a ready to load condition. Under these conditions it is desirable to enable engine operation and specifically to provide for high altitude starting. 
   The fuel-air ratio within the combustor  12  is preferably regulated within a range of approximately 0.027 to 0.041. Fuel-air ratios are related as a normalized equivalent ratio. The normalized equivalent ratio is a measure known to those skilled in the art for relating desired fuel-air ratios with different fuel grades and compositions. The combustor  12  of this invention operates at an approximate normalized equivalent ratio range between 0.40 and 0.60. The lower equivalent ratio provides more air than fuel. This range of fuel-air mixture minimizes flame temperature. Minimizing flame temperature within the combustor  12  provides for lower nitrous oxide emissions. Lower nitrous oxide emissions are desirable to minimize environmental impact. The fuel-air ratio disclosed is for example purposes and a worker with the benefit of this disclosure would understand that other fuel-air ratios are within the contemplation of this invention. 
   During a starting condition, the gas turbine engine assembly  10  performs optimally at higher fuel-air mixtures within the combustor  12 . The selected fuel-air ratio within the combustor  12  provides improved high altitude starting performance. 
   The same conditions that are desirable for high altitude starting are not desirable for operating the gas turbine engine assembly  10  under full load to provide maximum required amount of power. Increasing the amount of power produced by the gas turbine engine assembly  10  is accomplished by increasing fuel volume within the combustor chamber  14 . The second plurality of injectors  24  for this invention injects fuel into the intermediate zone  32  during ready engine load conditions. The increased volume of fuel-air mixture within the combustor  12  provides the desired increase in engine power. This is accomplished without increasing the flame temperature within the combustor chamber  14  and thereby without an increase in the levels of nitrous oxide emission from the combustor  12 . 
   Referring to  FIG. 2 , another cross-sectional view of the gas turbine engine assembly  10  is illustrated. The first plurality of injectors  22  include injectors all having dual orifices  36  ( FIG. 3 ). The orifices  36  are directed both towards the primary zone  30 . The second plurality of injectors  24  includes a single orifice  38  ( FIG. 3 ) directed towards the intermediate zone  32 . During initial starting conditions fuel is emitted into the combustor chamber  14  only by the first plurality of injectors  22  into the primary zone  30 . After the gas turbine engine assembly  10  has attained ready to load conditions, fuel is emitted from the second plurality of injectors  24  into the intermediate zone  32  that is adjacent the outlet portion  20  of the combustor chamber  14 . 
   The increase in fuel-air volume within the combustor  12  provides the desired increases in engine power. Although, engine power is increased, the flame temperature is not increased because a consistent fuel-air mixture ratio is disposed throughout the entire combustor chamber  14 . The only increase is in the volume of fuel-air mixture. The selective actuation of the second plurality of injectors  24  produces increased engine power with out an increase in flame temperatures. Further, the selective actuation of the first and second pluralities of injectors  22 ,  24 , provide for desired operation of the gas turbine engine assembly  10  both at initial starting conditions and during engine load operating conditions. 
   Referring to  FIGS. 3 and 4 , the combustor  12  is shown with the first and second plurality of injectors  22 ,  24  disposed radially about the combustor  12 . The first and second plurality of injectors  22 , 24  are supplied with fuel by fuel lines  25 . Preferably, each of the injectors  22 , 24  is mounted within the combustor  12  between the intermediate and primary zones  30 , 32  as shown in  FIGS. 1 and 2 . Further, the first and second plurality of injectors  22 , 24  are spaced an equal distance about the outer circumference of the combustor  12 . 
   In this exemplary embodiment the first plurality of injectors  22  includes eight injectors each having dual orifices  36 . The second plurality of injectors  24  includes four injectors each including the single orifice  38 . Although, specific numbers and positions of injectors are illustrated a worker with the benefit of this disclosure would understand that different configurations and types of injectors are applicable to this invention. 
   Operation of the gas turbine engine assembly  10  of this invention includes the steps of introducing fuel into the primary zone  30  within the combustor chamber  14  with the first plurality of injectors  22 . Fuel is injected into the primary zone  30  to provide a desired fuel-air ratio that provide favorable and reliable engine starting characteristics at high altitudes. The first plurality of injectors  22  operate alone to introduce fuel into the combustor chamber  14  from initial start up to the beginning of load application on the gas turbine engine assembly  10 . 
   Increased power for the application of load to the gas turbine engine assembly  10  is provided for by actuation of the second plurality of injectors  24 . The second plurality of injectors  22  engages to introduce fuel into the intermediate zone  32  within the combustor chamber  14 . The introduction of fuel into the intermediate zone  32  provides the increase in fuel-air mixture volume that provides the desired engine power output. The increase in volume without increasing the fuel-air mixture ratio provides for the desired power output without increasing the temperature within the combustor  12 . The stable and reduced flame temperature within the combustor  12  produces substantially less nitrous oxide emissions as compared to conventional gas turbine engines. 
   The combustor  12  according to this invention provides optimal operating conditions both during initial start up and during maximum engine loads. This is accomplished by selectively actuating the first and second plurality of injectors  22 ,  24  according to the desired operating conditions. Further, the angled effusion openings  40  swirl air and fuel entering the combustor chamber  14  to provide a consistent uniform pattern factor and flame temperature throughout the entire combustor  12 . The spin of fuel-air mixture within the combustor chamber  14  along with the change in the volume of the fuel-air mixture burned within the combustor chamber  14  optimizes combustor performance. The change of the volume of the fuel-air mixture is independent of the change in the fuel-air ratio that remains consistent during the entire operation from initial start up to maximum engine load. Providing a consistent fuel-air mixture that provides reduced flame temperatures during combustion that in turn decreases in nitrous oxide emissions. 
   Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.