US2770096A

US2770096A - Continuous combustion chamber with air flow and turbulence controlled by flame frontposition

Info

Publication number: US2770096A
Application number: US309655A
Authority: US
Inventors: Homer M Fox
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1952-09-15
Filing date: 1952-09-15
Publication date: 1956-11-13
Anticipated expiration: 1973-11-13

Description

New 13, 1956 FOX 2,770,096

CONTINUOUS COMBUSTION CHAMBER WITH AIR FLOW AND TURBULENCE CONTROLLED BY FLAME FRONT POSITION Flled Sept 15 1952 2 Sheets-Sheet l INVENTOR. H. M. FOX

ATTO R NEYS Nov. 13, 1956 H. M. FOX

CONTINUOUS COMBUSTION CHAMBER WITH AIR FLOW AND NCE CONTROLLED BY FLAME FRONT POSITION TURBULE Filed Sept. 15, 1952 2 Sheets-Sheet 2 INVENTOR.

H. M. FOX MJWLM g ZM? ATTORNEYS United States Patent CONTINUQUS COMBUSTION CHAMBER WITH AIR FLOW AND TURBULENCE CGNTROLLED BY FLAn /IE FRONT PGSITION Homer M. Fox, Bartlesvilie, Okla., assignor to Phiiiips Petroleum Company, a corporation of Delaware Application September 15, 1952, Serial No. 309,655

Claims. (Cl. 60-4919) This invention relates to continuous combustion chamfbers wherein finely divided fuel is burned in air. In a more specific aspect this invention rel-ates to continuous combustion chambers employed in a power plant wherein the products of combustion operate a turbine. In another specific aspect this invention relates to apparatus for stabilizing the location of the flame front in the combustion chamber by varying the fuel-air ratio and the amount of turbulence in the combustion chamber. In another aspect this invention relates to an apparatus for varying the fuel-air ratio and the amount of turbulence in the primary combustion chamber employed in connection with a gas turbine power plant.

The function of the combustion chamber of a turbojet engine is to provide the component into which fuel is introduced and burned so as to raise the temperature of the working fluid to the desired value. Division of the combustion chamber into combustion zones is secured by constructing the walls of the burner tube of the combustion chamber with perforations or holes so that only a portion of the air supplied to the engine is admitted to the region where fuel is injected {primary zone) and the remainder of the air is admitted to a region where combustion is quenched (secondary zone). For the purpose of this disclosure such burner tube will be designated as a tubular type burner tube and is applicable in a turbo-jet engine employing a single annular combustion chamber or a plurality of individual combustion chambers. The liquid fuel to be burned is injected through a pressure jet atomizer, prevaporizer or other suitable means into the primary combustion zone where zones rich in fuel and zones rich in air are formed. Upon the completion of suitable conditions for combustion, including fuel vaporization, formation of a flammable fuel-air mixture, and pre-combustion reactions, a region of intense reaction, defined as a flame front, is established. This region occurs as a fairly sharp break and causes the wall of the burner tube surrounding the region of intense combustion to become visibly hot.

Because of limitations of material of construction of turbine blades, temperatures in excess of 2000 F. cannot be utilized in the operation of present gas turbine engines and the possibility of the formation of excessive high temperatures is reduced by maintaining the over-all fuelair ratio between the values of about to M This over-all fuela-ir ratio is generally below or barely within the limits of flammability, and combustion under these conditions is either impossible or very unstable. Consequently, the flame tube of the combustion chamber is divided into two or more combustion zones and in one of these zones an approximately stoichiometric fuel-air mixture is formed under full load conditions so as to obtain high temperature and thus elficient combustion. In the other combustion zones, the combustion gases are diluted with air to insure complete combustion and to reduce the temperature of the combustion products.

Under ordinary operating conditions, such as are encountered at low altitude and during normal cruising "ice speed, the position of the flame front is comparatively close to the fuel nozzles. As the severity of inlet conditions increase, such as the lowered pressure and temperature which accompany an increase in altitude of the aircraft, the formation of a combustible mixture occurs at a point somewhat further downstream from the ideal location of the flame front. Movement of the flame front downstream in the combustion chamber results in a smaller volume for combustion before quenching by the large volume of secondary air and, therefore, a reduction in the efliciency and stability of combustion.

Under comparatively mild conditions of operation involving low mass air velocity, the flame front is located at a relatively short distance from the fuel nozzles. The presence of the flame near the fuel nozzle is undesirable since excess heat in this zone results in over heating and coking of the nozzles and at least some parts of the walls of the burner tube. In some combustion chambers, the movement of the flame front upstream chokes off the primary air and causes the primary combustion to be overly rich, resulting in combustion instability, inefiiciency, and blowout. Merely providing additional openin-gs in the combustion chamber tube wall so as to provide increased primary zone combustion results in unsatisfactory operation u-nder more severe conditions.

Each of the following objects will be attained by the aspects of this invention. It is an object of this invention to provide apparatus for maintaining the flame front in a combustion chamber substantially at the ideal location for stable combustion. It is another object to provide a continuous combustion chamber wherein the flame front is maintained at or near the ideal location by varying the fuel-air ratio and the turbulence of the fuel-air mixture in the primary combustion zone in accordance with temperature changes. Another object is to provide a means for varying the fuel-air ratio in accordance with the location of the flame front in the primary combustion zone. Another object is to provide a means for varying turbulence of the fuel-air mixture in the primary combustion zone in accordance with the location of the flame front. Still another object is to provide a means for maintaining stable combustion in a continuous combustion chamber by means of controls responsive to temperature changes. Other objects and advantages will be apparent to one skilled in the art upon reading the de scription and the drawing of the disclosure of this invention.

I have discovered apparatus for improved operation of a turbo-jet engine having a tubular burner tube design whereby clean, stable, and eflicient combustion is maintained throughout a wide range of operating conditions by controlling the fuel-air ratio and the turbulence of the fuel-air mixture in the primary combustion zone of the combustion chamber, in accordance with the location of the flame front in the burner tube. Regulation of the fuel-air ratio and turbulence of the fuel-air mixture in the primary combustion zone maintains the flame front in the ideal location in the primary zone and reduces a tendency, with changes in operating conditions of the aircraft, for the flame front to be displaced either downstream into the quenc'hing'zone or upstream toward the fuel nozzles.

The various aspects of my invention are accomplished by employing variable louvers or baffles located in the burner tube openings so as to regulate the amount of air to the primary combustion zone and to improve turbulence and thus maintain the flame front in an optimum location. These louvers or baflies are actuated by a thermal responsive member, for example, a bimetallic strip so that the louvers are caused to move to admit more air or are caused to project into the primary combustion zone to cause an increase of turbulence in accordance with the location of the flame front in the primary combustion zone. in each primary zone opening if necessary to effect adequate changes in fuel-air composition and turbulence of the fuel-air mixture in the combustion zone, but in some combustion chamber designs the location of the louvers in a few specific air passages is suflicient to provide adequate regulation of the composition and turbulence of the fuel-air mixture.

The position of the louvers in the burner tube wall openings depends on the location of the flame in the burner tube as detected by a suitable sensing means. Various apparatuses are available for detecting either the location of the flame front or the approach of a state of unstable combustion in the combustion chamber and any of these detection means can be adapted to control the position of the louvers. In one embodiment of my invention, a temperature sensitive element constructed of two metals of dissimilar coeflicients of thermal expansion, such as a thermostat, is used to determine the location of the flame front. This temperature sensitive element is constructed by rigidly attaching narrow flat strips of dissimilar metals together by some suitable means, so as to form a single bimetallic strip in which any movement of these metallic strips relative to each other is restricted, but an arching or bending deformation of the bimetallic strip takes place in the presence of a change in temperature. The arching or bending movement of the bimetallic strips is employed, either directly or through suitable linkages, to vary the position of the louvers in the burner tube wall openings when this bimetallic strip is rigidly attached to the surface of the burner tube at some location where changes in the location of flame front, and therefore the temperature, can be detected. The bimetallic strip can be mounted either on the inside surface of the burner tube or on the outer surface of the burner tube. Many combinations of metals are available for the formation of a bimetallic strip with the desired temperature characteristics. One combination is a member composed of ferro-nickel and Delhi steel of S-inches length and 0.1-inch thickness. in this bimetallic strip a temperature change of 540 F. results in a movement of the free end of 0.3-inch in a direction normal to the plane of the flat strip. The bending action of the strip can be increased by either increasing the length or decreasing the thickness of the strip.

In the drawing Figure l is a longitudinal axial section of the primary combustion zone of a combustion chamber of this invention showing the controls in place on the burner tube.

Figure 2 is a plan view of a fuel-air ratio control of this invention.

Figure 3 is a sectional view along line 33 of Figure 2.

Figure 4 is a plan view of a fuel-air turbulence control of this invention.

Figure 5 is a sectional view along line 55 of Figure 4.

Figure 6 is a plan view of a combined fuel-air ratio and turbulence control.

Figure 7 is a sectional view along line 77 of Figure 6.

Figure 8 shows in schematic form a conventional turbojet engine in which the devices of this invention are advantageously employed.

Figure 2 is a plan view of a section of a combustion chamber and shows an arrangement of a bimetallic element attached to a louver for varying the fuel-air ratio in the primary combustion zone.

Figure 3 is a sectional view along line 3-3 in Figure 2, showing a louver in substantially extended position so as to direct a sutiicient quantity of air into the primary combustion zone to maintain combustion for normal operating conditions. As shown in Figure 2 air opening 10 in the burner tube wall 11 is rectangular in shape, however, openings of other shapes, including circular, can be used. One end of bimetallic element 12 is attached with rivets 13 or other suitable means to the surface of burner tube 11 and the other end is free to curl towards the surface The louvers can be placed of burner tube 11 and thus cause the center portion of bimetallic element 12 to arch away from the surface of burner tube 11. Louvers 14 of rectangular shape are rotatably attached to the downstream edge of opening 10 by some means 15 and rigidly attached to straight memer 16 which is rotatably attached to bimetallic element 12 in such a manner that the arching movement of bimetallic element 12 away from burner tube 11 can be applied through rotatable mounting 15 so as to swing louver 14 further into the annular or air passage 17 formed be tween combustion chamber outer shell 18 and burner tube 11 so as to direct air through opening 10 into the primary combustion zone. In a similar manner a flattening of bimetallic element 12 results in the application of a force through rotatable mounting 15 so as to cause louver 14 to be moved toward burner tube 11 to direct less air from the annular chamber 17 through opening 10 and also to partly close the opening 16 to the passage of air to the primary combustion zone. 7

In the operation of this modification of my invention, bimetallic element 12 is arched away from the burner tube wall 11 and louver 14 is substantially extended into the annular chamber 17 when the flame is in its ideal position. When the flame front moves downstream from its ideal position bimetallic element 12 flattens out and moves louver 14 closer to opening 10 so as to direct less air into the primary combustion zone and causes the flame front to move upstream to its ideal position. The presence of the flame near the nozzle during idling causes bimetallic element 12 to arch further away from the wall of burner tube 11 and thus moves louver 14 further into the annular chamber 17 so as to direct more air through the opening 10 into the primary combustion zone and thereby causes the flame front to move downstream.

Figure 4 is a plan view of a section of a combustion chamber showing two primary combustion zone air inlet openings and an arrangement of a bimetallic temperature sensitive element attached to the surface of the burner tube so as to control the positions of both of the baflies in the openings of the wall of the burner tube.

Figure 5 is a sectional view along line 55 of Figure 4 but showing a baffle 23 in a fully retarded position. One end of the bimetallic strip 20 is rigidly attached to the burner tube 11 by rivets 22 and the other end is free to curl toward the surface of burner tube 11 thus causing the center portion of the strip to arch away from the surface. Baffles 23 are rotatably attached to the downstream edges of the burner tube airopenings 24 by some means 25 and rigidly attached to a straight member 16 which is rotatably attached to the bimetallic strip 20 in such a manner that the arching movement of bimetallic strip 20 away from burner tube 11, as a result of an increase in temperature, is applied through the rotatable mounting 25 to swing baflies 23 toward the burner tube wall and out of the path of primary combustion zone air entering through openings 24. In a similar manner, a decrease in temperature results in a flattening ofthe bimetallic strip and the application of a force through rotatable mounting 25 so as to cause batfles 23 to be moved away from the burner tube wall 11 and into the path of air passing through the air openings 24 so as to promote turbulence in the primary combustion zone.

In the operation of this embodiment of the present invention the bimetallic strip is flat and against theburner tube wall when the latter is cold or the flame front has moved downstream from the ideal position but it is bent away from the surface of the burner tube when the flame front is in the ideal position. Consequently,- when the combustion chambcr is cold or the flame has moved downstream, the baflles are fully extended awayfrom the walls of the burner tube and have a maximum effect on turbulence in the primary combustion zone. The baffles, therefore, aid in starting the engine. After start- .ing, but while the engine is idling, the air flow is-relatively low and the mixing of fueland air is achieved rapidly so that the flame is maintained at or near its ideal position with little or no turbulence generated 'by the bafiles. The presence of the flame near the fuel nozzle during idling after starting heats the bimetallic strip causing it to bend away from the burner tube wall and thereby swings the 'bafiles toward the burner tube wall so that they have less effect on the turbulence of the primary air. Upon acceleration, the air flow is increased so that mixing of the fuel and air can be lessened and the flame front tends to move downstream. The resultant cooling of the bimetallic strip causes it to flatten out and thereby move the baflles away from the burner tube walls and into the path of air flow so as to increase the turbulence of the primary air and fuel mixture and cause the flame to move back up stream toward its ideal position.

The louvers or bafiies which vary the fuel-air ratio and those which control the turbulence of the air-fuel mixture in the primary combustion zone can be used either separately or together. 'Figure 1 shows these two types of elements being used alternately in connection with a burner tube of a combustion chamber in order to achieve full benefit from each type of control. Other arrangements are obviously possible within the scope of this invention and can be employed to meet a particular requirement.

Figure 6 is a plan view which shows a modification wherein baflies or louvers designed to control fuel-air ratio and those designed to control turbulence in the primary combustion zone are combined and incorporated in a single burner tube wall opening.

Figure 7 is a sectional view taken along line 7-7 of Figure 6. The fuel-air ratio controlling bafile 30 and the turbulence controlling baifle 31 are actuated by bi- .ietallic strip 32 operating the bafiles through linkage 33 so that when the bimetallic strip 32 is arched away from the burner tube 11 as a result of heat from the flame front, as shown in Figure 7, the fuel-air ratio baflle will be in extended position so as to divert more air into the primary combustion zone through opening 34 and the turbulence producing baffle will be retracted so as to produce the minimum of turbulence. When the bimetallic strip is not heated by the flame front and lies flat against the burner tube, the fuel-air ratio controlling bafiie closes the opening in the burner tube and the turbulence controlling baffle is in extended position so as to cause maximum turbulence in the air admitted through openings not covered by bafl les.

Varations and modifications are possible within the scope of the disclosure of the present invention, the essence of which is that combustion stability in a continuous combustion chamber is improved by means of louvers or baffles in the openings of the burner tube which control the fuel-air ratio and the amount of turbulence in the primary combustion zone and are actuated by temperature sensitive members controlled by the location of the flame front in the burner tube.

I claim:

1. In a continuous combustion power plant a combustion chamber comprising an outer shell; a burner tube disposed within said shell and having a plurality of open ings connecting the annular chamber formed between said burner tube wall and said shell with the interior of said burner tube; an air inlet communicating with said annular chamber; a fuel injector in said burner tube chamber; means for igniting a resulting fuel-gas mixture; a plurality of battles extending through said openings into at least one of said chambers upstream from the flame front resulting from combustion of said fuelair mixture; and temperature responsive elements secured to said burner tube and operatively connected to said ba'fiies so as to vary their positions in said chamber in response to changes in position of the flame front in said burner tube.

2. A combustion chamber comprising an elongated outer shell; a burner tube disposed within said shell and having a plurality of openings connecting an annular 'air passage chamber formed between the burner tube wall and the outer shell with interior of the burner tube; a plurality of fuel air ratio controllers arranged in operative relationship to said openings comprising a baflle located within and movably secured to the downstream edge of a said opening; and a temperature responsive member secured to the wall of said burner tube and operatively connected to said baffle so that said baifle substantially covers said opening when said temperature responsive member is not heated by the flame front in said combustion zone and said baifle uncovers said opening and projects into said chamber when said temperature responsive member is heated by the said flame front.

3. A combustion chamber comprising an elongated outer shell; a burner tube disposed within said shell and having a plurality of openings connecting an annular air passage chamber formed between the burner tube wall and the outer shell With the interior of the burner tube; a plurality of turbulence producers arranged in operative relationship to said openings comprising a bafile located within and movably secured to the downstream edge of a said opening; and a temperature responsive member secured to the wall of said burner tube and operatively connected to said baffle so that said baffle projects into said burner tube when said temperature responsive member is not heated by the flame front in said burner tube and said baffle is caused to lie substantially parallel with the wall of the burner tube when said temperature responsive member is heated by said flame front.

4. A combustion chamber comprising an elongated outer shell; a burner tube disposed within said shell and having a plurality of openings connecting an annular air passage chamber, formed between the burner tube wall and the outer shell, with the interior of the burner tube; a plurality of fuel-air ratio controllers arranged in operative relationship to said openings comprising a bafile located within and movably secured to the downstream edge of a said opening; a temperature responsive member secured to the wall of said burner tube and operatively connected to said baflie so that said baflle substantially covers said opening when said temperature responsive member is not heated by the flame front in said burner tube and said baifle uncovers said opening and projects into the annular air passage chamber when said temperature responsive member is heated by said flame front; a plurality of turbulence producers arranged in operative relationship to said openings comprising a bafile located within and movably secured to the downstream edge of a said opening; and a temperature responsive member secured to the wall of said burner tube and operatively connected to said baffie so that said baflle projects into said burner tube when said temperature responsive member is not heated by the flame front and said baflle is caused to lie substantially parallel with the wall of the burner tube when said temperature responsive member is heated by said flame front.

5. The apparatus of claim 4 wherein the fuel-air ratio controllers and the turbulence producers are located in alternate openings.

6. The apparatus of claim 4 wherein the fuel air ratio controllers and the turbulence producers are located in the same openings.

7. A combustion chamber comprising an elongated outer shell; a burner tube disposed within said shell and having a plurality of openings connecting an annular air passage chamber, formed between the burner tube and shell, with the interior of the burner tube; a plurality of fuel-air ratio controllers and air turbulence controllers arranged in operative relationship to said openings cornprising a first baflle located within and movably secured to the downstream edge of a said opening; a temperature responsive member secured to the wall of said burner tube and operatively connected to said baflle so that said baffle substantially covers said opening where said temperature responsive member is not heated by a flame front in said burner tube and said bafiie uncovers said opening and projects into the annular air passage when said temperature responsive member is heated by said flame front; a second baifie movably secured to the downstream edge of said opening and disposed within said burner tube; a linkage connecting said first baffle and said second bafile so that when said first baffie uncovers said opening and extends into said air passage, said second baffle will be retracted adjacent said burner tube wall and when said first bafile covers said opening said second baffle will be extended into said burner tube.

8. In a continuous combustion power plant, the improvement which comprises means for determining the position of the flame front in the burner tube; and means operatively connected with the first said means for varying the fuel-air ratio and the amount of turbulence of the fuel-air mixture in the primary combustion zone in response to the position of the flame front in the burner tube.

9. In a continuous combustion power plant, the improvement which comprises means for determining the position of the flame front in the burner tube; and means operatively connected with the first said means for varying the fuel-air ratio in the primary combustion zone in response to the position of the flame front in the burner tube.

10. In a continuous combustion power plant, the improvement which comprises means for determining the position of the flame front in the burner tube; and means operatively connected with the first said means for varying the amount of turbulence of the fuel-air mixture in the primary combustion zone in response to the position of the flame front in the burner tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,227,666 Noack Jan. 7, 1941 2,457,157 King Dec. 28, 1948 2,464,791 Bonvillian et a1 Mar. 22, 1949 2,572,723 Hildestad Oct. 23, 1951 2,621,477 Powter et a1 Dec. 16, 1952 2,655,787 Brown Oct. 20, 1953