Abstract:
A apparatus and method for improving combustion by improving at least one of temperature distribution in the combustor, pressure distribution around the combustor and combustion noise level in the combustor, by redistributing air around the combustor to modify the structure of the air flow prior to entry into the combustor.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a method and apparatus for improving combustion, and particularly gas turbine engine combustion.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the combustion of fuels in a combustion chamber like that of an industrial gas turbine or an aircraft gas turbine engine, the combustion process can cause instabilities or pressure fluctuations which, under unfavourable conditions, present undesirable combustion noise and a poor dynamic temperature distribution.  
         [0003]     In particular, there is a need to improve temperature distribution and noise level of gas turbine engine combustion, and particularly so in APU for aircraft.  
       SUMMARY OF THE INVENTION  
       [0004]     One object of the present invention is to provide improved combustion, and particularly that which would be beneficial to gas turbine engines.  
         [0005]     In another aspect, the invention provides at least a gas turbine engine comprising: a combustor portion including at least one combustor, the combustor having a plurality, of holes therein for admitting combustion air into the combustor; a casing defining at least one chamber therein, the chamber containing the combustor and a volume of air around at least a portion of the combustor; a compressor portion communicating with the chamber via a compressor outlet for delivering compressed air to the chamber for subsequent admission into the combustor; and a ring extending into the chamber substantially continuously around the chamber so as to extend partially into an air flow exiting the compressor outlet into the chamber, the ring sized and positioned in the chamber to, in use, cause a step change in direction and pressure of at least a portion of the air flow, the step change adapted to effect a redistribution of air around the combustor to thereby achieve at least one of reduced combustion noise and more uniform temperature distribution in the combustor.  
         [0006]     In another aspect, the invention provides at least an apparatus for improving combustion in a gas turbine engine, the gas turbine engine comprising at least a compressor portion, a combustor and a chamber housing the combustor, the compressor portion having an outlet interfacing with the chamber for delivering a flow of compressed air to the chamber, the combustor having holes therein interfacing with the chamber and adapted to permit air in the chamber to enter the combustor for combustion, the apparatus comprising: means positioned fluidly intermediate the outlet and the combustor for aerodynamically tripping the compressed air flow entering the chamber to thereby create a step change in the air flow prior to entry into the combustor, said means adapted to thereby decouple acoustic and hydraulic fluctuation components in the air flow prior to entry of the air flow into the combustor.  
         [0007]     In another aspect, the invention provides at least a gas turbine engine comprising: a gas generator portion including at least a compressor, a combustor and a chamber around the combustor, the gas generator in use having an air flow from the compressor entering the chamber and guided thereby to the combustor; the air flow providing a source of combustion air to the combustor; and at least one trip disposed in the chamber at a location fluidly intermediate the compressor and the combustor, the trip adapted to extend into the air flow and extend substantially transversely relative to an initial direction of the air flow in the chamber, the trip adapted in use to create a predetermined step change increase in pressure drop of the air flow to thereby effect a predetermined air flow redistribution in the chamber, said air flow redistribution predetermined to improve at least one of an air pressure distribution outside the combustor and a fluctuation phase shift in the air flow adapted to reduce combustion noise.  
         [0008]     In another aspect, the invention provides at least a method for improving at least one of a temperature distribution and a combustion noise level in a combustor of a combustion system, the combustion system having an air source for providing a flow of compressed air to a chamber housing the combustor, the combustor having holes therein for admitting the compressed air into the combustor for combustion therein when mixed with fuel and ignited, the method comprising the step of: aerodynamically tripping the flow of compressed air downstream of an entry point for said air into the chamber and before the flow of air enters the combustor, the step of tripping adapted to impart at least a step change in pressure drop of at least a portion of the flow of air, the step change adapted to decouple fluctuation components in the flow of air prior to entry of the air into the combustor.  
         [0009]     In another aspect, the invention provides at least a method of providing a gas turbine engine, the method comprising the steps of: determining a configuration for a compressed air system, a combustor and a casing chamber surrounding the combustor, the configuration including an air flow path from compressed air system through the casing chamber and into the combustor; determining an initial operating air pressure distribution occurring in the compressed air in the chamber around the combustor; determining a desired air pressure redistribution in the compressed air in the chamber around the combustor, the redistribution adapted to provide at least one of reduced combustion noise and improved temperature distribution in the combustor; and introducing an intervention in the casing chamber, the intervention extending into the flow path and adapted to effect the determined air pressure redistribution.  
         [0010]     In another aspect, the invention provides at least a method of improving combustion, the method comprising the steps of: providing a compressed air flow, the compressed air flow having an acoustic and hydrodynamic structure imposed during a compression process; restructuring the acoustic and hydrodynamic structure to provide a preselected second acoustic and hydrodynamic structure, the second structure preselected to cause a acoustic and hydrodynamic phase shift in at least a portion of the compressed air flow, the phase shift being selected adapted to reduce combustion noise; providing the restructured compressed air flow to a combustor for use in combustion.  
         [0011]     In another aspect, the invention provides at least a method of improving combustion in a gas turbine engine, the method comprising, the steps of: selecting a gas turbine engine, the engine having at least a compressor providing a source of compressed air, a combustor and a chamber surrounding the combustor, the compressor, chamber and combustor in serial fluid communication for transmitting the air from the compressor to the combustor for combustion; and modifying the gas turbine engine by inserting at least one aerodynamic trip into the chambers the trip adapted to effect at least one of a pressure redistribution around the combustor and a phase shift in pressure fluctuations in at least a portion of the air in the chamber, the phase shift adapted to reduce combustion noise. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Having thus generally described the nature of the present invention, reference will now be made to the accompanying drawings, showing by way of illustration the preferred embodiment thereof, in which:  
         [0013]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine incorporating one embodiment of the present invention;  
         [0014]      FIG. 2  is a cross-sectional view of Detail  8  of  FIG. 1 ;  
         [0015]      FIG. 3  is a front elevational view of an aerodynamic trip ring of  FIG. 2 ;  
         [0016]      FIG. 4  is a cross-sectional view taken along Line  4 - 4  of  FIG. 3 ;  
         [0017]      FIG. 4   a  is a cross-sectional view similar to  FIG. 4  or an alternate embodiment;  
         [0018]      FIGS. 5   a  and  5   b  depict another alternate embodiment of the invention;  
         [0019]      FIGS. 6   a  and  6   b  depict a further alternate embodiment of the invention; and  
         [0020]      FIGS. 7   a  and  7   b  depict another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring to  FIG. 1 , a gas turbine engine  10 , which is illustrated as an APU but can be any type of gas turbine engine, includes an embodiment of the present invention. Engine  10  generally comprises a compressor region  12 , a combustor region  14  and a turbine region  16 . The compressor region  12  generally includes a high pressure compressor  18  for providing a high pressure compressor air flow for combustion and for cooling of the engine. A compressor diffuser  20  is positioned downstream of the high pressure compressor  18  and extends into the combustor region  14  for reducing the velocity which increases the pressure of compressor air flow and for delivering the compressor air flow to the combustor region  14 . According to the present invention, a tripping device, in this embodiment preferably an aerodynamic trip ring  22 , is provided in the combustor region  14  for intervening in the compressor air flow before the compressor air flow enters a combustor  24  for combustion, as will be described in detail with reference to  FIG. 2 , below. The turbine region  16  includes high pressure turbine  17  and powering turbine  19 . The combustion gases generated from the combustor region  14  enter the turbine region  16  for powering the respective turbines  17  and  19 .  
         [0022]      FIG. 2 , taken from Detail  8  of  FIG. 1 , depicts the combustor region  14  in greater detail. Generally, the combustor region  14  is defined by a substantially cylindrical casing  26 , preferably surrounding at least a downstream section of the compressor diffuser  20  and the combustor  24 , (which is shown as an annular combustor, though any suitable combustor shape may be used), thereby forming a chamber  28  surrounding a volume of air and the combustor  24 . The combustor  24  has a radially outer side  24   a  and a radially inner side  24   b . The casing serves to help direct the compressor air flow from the compressor diffuser  20  to the combustor, and thereby defines a flow path portion  46  downstream of the compressor diffuser  20  to the combustor  24 . The compressor  24  is supported within the chamber  28  by a suitable support structure  30  which secures the annular combustor  24  to the casing  26 . A plurality of fuel nozzles  32  extend into the combustor  24 . The combustor  24  further includes a plurality of apertures  25  therethrough so that the chamber  28  is in fluid communication with a combustor chamber  34  defined within the combustor  24 . The fuel nozzles  32  inject fuel into the combustion chamber  34  to be mixed with compressor air flow having entered from the chamber  28  into the combustor  24 . The fuel and air mixture is then ignited to generate expanding combustion gases, which then enter the turbine section  16  for driving the high pressure turbine  17  and the power turbine  19 .  
         [0023]     The compressor air flow exiting the compressor region generally carries fluctuation energy which is generated substantially during the air compressing course. The fluctuation energy carried in the compressor air flow includes both acoustic and hydraulic fluctuation components which present a broad band of high and low frequency signals. These high and low frequency signals when being delivered into the combustor  24  by the compressor air flow, will be amplified during the combustion reaction in the combustion chamber  34 , thereby creating a high level of the combustion noise. Furthermore, the fluctuation energy carried and delivered into the combustor  24  by the compressor air flow, adversely affects an even and uniform pressure distribution, which causes the less than optimum mixing of fuel with the compressor air flow within the combustor, thereby resulting in a poor dynamic temperature distribution within the combustion chamber  34 , which in turn exacerbates amplification of the combustion noise level.  
         [0024]     The inventor has found that improvement can be achieved if the acoustic and hydraulic fluctuation components of the compressor air flow are decoupled before entry into the combustor. Hence, in one aspect, the invention presents an aerodynamic trip to effect a decoupling of the acoustic and hydraulic fluctuation components of the compressor air flow, as will now be described in more detail.  
         [0025]     The aerodynamic trip ring  22  more clearly shown in  FIGS. 3 and 4 , is made of, for example, a suitable metal material or any other material suitable for the application and subject operating conditions, and includes a mounting portion including an axial section  36  and an outer radial section  38 , and an inner radial trip section  40 . The outer radial section  38  extends radially outwardly from the axial section  36  at one side thereof, and the inner radial section  40  extends radially inwardly from the axial section  36  at the other side thereof. A plurality of mounting openings  42  are provided in the outer radial section  38  in a circumferentially spaced apart relationship. The inner radial section  40  preferably includes an inner periphery  44  beveled at the outer side thereof.  
         [0026]     Referring to  FIGS. 2-4 , the casing  26  of a gas turbine engine is configured with an upstream section  46  and a downstream section  48  which are bolted together by a flange connection  50 . In such a situation, the aerodynamic trip ring  22  is preferably secured to the inner side of the casing  26  by positioning the outer radial section  38  between the upstream and the downstream sections  47 ,  48  of the casing  26 , and by receiving the flange connection bolts (not indicated) extending through the mounting openings  42 . The axial section  36  of the aerodynamic trip ring  22  preferably has a radial dimension appropriate for abutting the inner side of the casing  26  in order to prevent the aerodynamic trip ring  22  from possible vibration caused by the effects of the fluctuation energy carried by the compressor air flow. The inner radial section  40  of the aerodynamic trip ring  22  extends into the flow path  46  of the compressor air flow within the chamber  28  downstream of the compressor diffuser  20 . The beveled inner periphery  44  faces the compressor diffuser  20  when the aerodynamic trip ring  22  is mounted within the chamber  28 .  
         [0027]     In use, the aerodynamic trip ring  22  surrounding the annular combustor  24  imparts a perpendicular directional component to the compressor flow exiting the compressor and passing by the trip ring  22 . The interaction of the air flow and the trip ring  22  creates a step change in the direction and pressure of the compressor air flow prior to entry of the air flow into the combustor  24 , which beneficially improves both temperature distribution in the combustion and combustion noise levels in the combustor.  
         [0028]     The trip creates a step change in a direction of at least a portion of the compressor air flow which is believed to thereby diffuse the hydraulic fluctuation energy in the compressor air flow. Diffusion of this energy promotes redistribution of compressor air around the combustor  24  promotes better air distribution uniformity inside the combustion chamber  34 , thereby resulting in better a mixing of the air and the fuel. Thus, the overall temperature distribution factor (OTDF) of the gas turbine engine combustion can be improved. The trip also causes a step change increase in the pressure drop in the air flow which, together with the direction change, results in an energy dissipation which is useful, when controlled according to the present teachings, in attenuating combustion noise. In general terms, the longer at least a portion of the compressor air flow remains in the chamber  28  before entering the combustor, the better decoupling of the acoustic and hydraulic fluctuation components of the compressor air flow can be achieved as a result of a time delay and phase shift on all frequency ranges in the air flow. The local pressure drop around the combustor may therefore be beneficially redistributed, and the duration the compressor air flow resides within the chamber outside the combustor may be beneficially altered to permit the fluctuation components of the compressor air flow to be decoupled so that a subtractive cancelling effect on combustion noise is achieved in the combustor. The present invention therefore achieves a beneficial decoupling of compressor acoustic and hydrodynamic fluctuations prior to entry into the combustor.  
         [0029]     The step change in direction is achieved by a redirecting function performed by the trip. The step change pressure drop is achieved by one or more of a flow restricting function, a turbulence intensity increasing function and flow separation function of the trip. All elements contribute to an energy dissipation in the flow, and a corresponding frequency shift in the flow&#39;s acoustic and hydraulic components. It will be understood that a step change is not a continuous change over a distance travelled by the air flow, but rather a discontinuity in direction and or pressure drop.  
         [0030]     The configuration, size and location of the trip can be determined depending on the desired direction change and desired pressure drop to achieve the desired percentage of air redistribution around the combustor. The redistribution preferably occurs upstream of air entry into the combustor and downstream of the inlet into the chamber. The trip is preferably placed at a reasonable distance, downstream so as not to cause choking, etc. The trip is preferably located close to the compressor outlet relative to the size of the chamber  28 . The trip is placed relative to the compressor outlet to restructure the flow exiting the compressor before that flow enters the combustor. For example, referring to  FIG. 2 , trip  22  nay be designed to cause 10% more air to be redistributed towards the inner wall of the annular combustor (i.e. the lower wall, as depicted in  FIG. 2 ), which may thereby achieve a better pressure distribution about the combustor, achieve a desired frequency shift in the flow, etc.  
         [0031]     Fuel or partial redistribution of air flow velocity and pressure and diffusion of fluctuation energy in the air flow are thus both achieved by introducing a step change in velocity and pressure to the air flow. The hydrodynamic and acoustic structure imposed by the compressor on the air flow can be restructured according to the designer&#39;s preference prior to delivery to the combustor for combustion. The invention therefore permits combustor noise and combustion performance to be improved for a given combustor and fuel nozzle configuration without making changes to the combustor and/or fuel nozzle configuration. This permits the designed to optimize those components according to another set considerations.  
         [0032]     Preferably, the pressure drop introduced by the trip will be not more than the pressure drop which is calculated to occur across the combustor in the same system operated without the trip present. The pressure drop selected by the designed will preferably range between 0 and this preferred maximum value.  
         [0033]     The use of the aerodynamic trip approach to affect the compressor air flow within the chamber  28  is a simple, convenient and practical approach executable entirely outside, the combustor  24 . The “tripped” compressor air flow permits a better temperature distribution and a relatively lower noise energy to be delivered to the combustion chamber  34 , and thereby permits the overall acoustic noise level of the gas turbine engine combustion to be intentionally and controllably reduced relative to prior art “untripped”, flows . . .  
         [0034]     The aerodynamic trip  22  may be secured to engine  10  using any suitable mounting means. For example, an aerodynamic trip ring  22  may include a mounting portion with only, the axial section  36  for mounting the inner radial trip section  40  to the engine. The mounting holes  42  or other mounting means may be defined in the axial section  36  of the mounting portion so that the aerodynamic trip ring  22  may be mechanically mounted directly to the inner side of the casing  22  at any selected axial position between compressor diffuser  20  and the support structure  30 . In such a configuration, the radial size of the axial section  36  should be properly fitted into an inner diameter of the casing  26 . Any other suitable manner of mounting or mounting configuration may be likewise be used, such chemical bonding, welding, brazing, interlocking or other mechanical attachment or the feature may be integrally provided on an existing component.  
         [0035]     The trip means is positioned fluidly intermediate the compressor and the combustor. The trip means may be mounted to the casing  26 , the combustor  24 , the support structure  30 , the compressor diffuser  20 , or other suitable location. Likewise, the trip need not be continuous or uniform around the combustor. For example, referring to  FIGS. 5   a  and  5   b , a non-continuous non-ring-like trip means  22 , particularly a plurality of baffle plates  22   a , which may be provided with or without openings (without is shown), and which may be placed in the flow path  46  of the compressor air flow, mounted to the compressor diffuser  20 . In another example shown in  FIGS. 6   a  and  6   b , trip means  22  may be a plurality of deflector members  22   b  mounted to the combustor. Referring to  FIGS. 7   a  and  7   b , trip means  22  may comprise multiple elements  22   c  extending into the flow path downstream of one another, etc.  
         [0036]     This, description is intended to be exemplary only and is not exhaustive with respect to possible variation of the present invention. While it is preferable to provide the trip means substantially entirely around the combustor  24  for substantially circumferentially uniformly affecting the compressor air flow, it is not necessary to achieve benefits as described herein. Multiple trips having different configurations may be used, according to preference. Any device, structure or mechanism which performs a function like that described may be used, and the invention is not limited to a conventional trip, per se. The present invention can be used with any compressor configuration (e.g. centrifugal, axial, etc.) or any other means by which a flow of preferably compressed combustion air is provided to an volume of air enveloping a combustor. Any combustor type, including can, cannular and annular type combustors, may be used. The volume or air around the combustor need not completely encircle or surround the combustor. The trip means is preferably arranged transversely relative to the original air flow outside the combustor, but need not be necessarily so. The trip means need not extend perpendicularly to the flow or radially relative to the engine centreline, those these are, preferred by the inventor. The present approach may also be used advantageously to decouple imposed instabilities such as that which may arise from any feedback loop between imposed pressure oscillations by the compressor and fluctuation of combustor equivalence ratio or heat dissipation rate. Modifications and improvements to the above-described embodiments of the present invention may therefore become apparent to those skilled in the art, and thus the foregoing description is intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.