US2616257A - Combustion chamber with air inlet means providing a plurality of concentric strata of varying velocities - Google Patents

Description

Nov. 4, 1952 F c. MOCK 2,616,257

COMBUSTION CHAMBER WITH Ali? INLET MEANS PROVIDING A PLURALITY OF CONCENTRIC STRATA OF VARYING VELOCITIES Filed Jan. 9, 1946 2 SHEETSSHEET l zIlI////IIII1". I v 9/ INVENTOR. QAwun'lI/////IIIlIl""' ATTOP/Vf) Nov. 4, 1952 F. c. MOCK 2,616,257

COMBUSTION CHAMBER WITH AIR INLET MEANS PROVIDING A PLURALITY OF CONCENTRIC STRATA 0F VARYING VELOCITIES Filed Jan. 9, 1946 2 SHEETSSHEET 2 1 N VEN TOR.

FPAA/A d/yam BY W Patented Nov. 4, 1952 COMBUSTION CHAMBER WITH AIR INLET MEANS PROVIDING A PLURALITY F CON QENTR-IC STRATA OF VARYING VELGCL' TIES Frank C, llrloclr, South Bend, Ind assignor to Bendix'A'viation Corporation, South Bend, Ind., a corporation of Delaware Application January 9, 1946, Serial No. 640,018

The present invention relates to burners, and particularly to burners wherein a fuel, either gaseous, liquid or powdered solid fuel, is injected into and burned in a moving column of air. Such burners are particularly adapted for use in aircraft power plants or engines of the gas turbine and/or jet propulsion types wherein compressed air is supplied to a chamber constituting part of the burner, at which'point it is heated by the combustion of fuel and the expanded air and products of combustion discharge through a gas, turbine for driving an air compressor and/or a propeller, after which the gases may be dis charged through a reaction tube to propel the aircraft or to assist the propeller in propelling the aircraft. v

This application contains subject matter divided out or my co-pending application Ser. No. 557,812 filed October 9, 1944, now Patent No. 2,581,275 plus modifications thereof, and hence may be considered as a continuation-impart of Ser. No. 557,812.

A burner of the aforesaid type is ofttimes subjected to conditions which render it extremelydiificult to maintain stable operation of the burner, or to obtain proper flame propagation and an effective fuel/air ratio over. the wide range of air flows to which the burner is sub jected. Thus, flow of fuel to the burner may at timesbe suddenly reduced to reduce engine speed, resulting in a low flame at the burner nozzle while at the same time the momentum of the engine may momentarily produce a high air flow tending to blow out the flame. Again, it. is de-- sirable that the burner ignite or start quickly and easily under all conditions of ai-r flow, both at the start of a flight and during flight of an aircraft. If there is delay in igniting the burner during the initial starting operation, excess fuel accumulates in both the burner tube andadjacent chambers, and then when the engine does. start, there is an intense flame and heat produced while the" accumulated fuel is burning. which tends to burn and warp parts in the immediate region of the flame; Another factor is so-called detonation or "blow-gut which may he a cause df'bu'rner failure, particularly at high engine powers, One source or" this noun-e; especially in tubular burners, is" the tendency or the burner to becomeunstame and reverberate somewhat like an organ'pip'e of similar dimensions'; and sometimes these reverberati'onsl build burner herein disclosed, a separate resonator 7' claims, (or. 39.65)

2 chamber is provided burner tube in communication with the main burner chamber and having a resonance fre-' quency tending to neutralize or dampen out the reverberations of the main burner chamber or tube.

An object of the invention is to provide a burner or generator of the type specified which will admit air under pressure into the burner chamber, and particularly the breech portion thereof in a manner such as to render the burner flame stable under widely varying conditions of airflow to the burner.

Another and more specific object is to provide a burner or generator for heating and expanding a'ir flowing thereto under pressure having calibrated air-inlet means which directs the air into the breech portion of the burner chamber in a plurality of concentric masses or strata of varying, velocities with the mass of lowest velocity in the immediate region of the burner nozzle.

Another object is to provide means in a burner whereby carbon formation on the fuel-delivery nozzle or nozzles as well as on the spark plugs or analogous ignition means is reduced to a minimum;

Another object is to provide an improved burner or generator unit particularly adapted for power plants of the gas turbine an/or j'et propulsion types, and wherein burner failure due to the foregoing and other causes is reduced to a minimum.

A further object is to improve and render more efficient burners or heat generators.

The foregoing and other objects and advantages will become apparent in View of the following description taken in conjunction withv the drawings", wherein:

Figure 1' is a substantially central longitudinal" sectional view of a burner embodying the features of the invention;

Figure 2 is a similar view of a modification structure;

Figure 3 is an end view of Figure 2 taken" as spray nozzle adapted for use with the burners" illustrated inthe preceding. figures;

Figure 7 is'an' enlarged section of the'end por'- tion of the nozzle of Figure 6; and" at the breech end of the a rotary compressor, not shown, driven by a I turbine, also not shown, having blades subjected to the dynamic action of heated and expanded air and products of combustion generated in the burner.

The burner of Figure l is similar to that disclosed in my copending application above noted; it consists of an outer cylindrical shell or wall 8 provided with a plurality of air inlet ports 9, to which air is supplied under pressure through the chamber 5. Within the breech portion of the outer shell 8 is another shorter cylinder or annulus it} having an outwardly tapered or inclined bafiie wall I i provided with a series of calibrated air inlet orifices !2. Within the annulus I is a third, still shorter cylinder or annulus [3 provided with an end bafile wall l4 also formed with a series of air inlet orifices H3. The air impact or breech end of the burner is provided with a baffle wall l6 formed with a series of annularlyarranged air-inlet orifices H, is and [9, which are preferably of progressively decreasing area or flow capacity as they approach the center of the said wall l6, said orifices ll, I8 and I9 opening into velocity-reducing chambers 20, 2| and 22 defined by the stepped cylinders Ill and I3 and a central bafile wall 23 formed with calibrated air inlet orifices 24. An ignitor 25, which may be of the electric sparking type supplied with current from a suitable source, not shown, is projected into the burner cylinder adjacent the tip of a burner nozzle 25. v

To more effectively obtain this velocity-reducing action, the aggregate area of orifices I2 is greater than the aggregate area of orifices H, the aggregate area of orifices I is greater than the aggregate area of orifices l8, and the aggre-.

gate area of orifices 24 is greater than the aggregatearea of orifices l9.

A combustion chamber constructed in this manner coacts with the fuel feeding system which supplies fuel to the chamber through the burner nozzle to insure localized fuel/air proportioning and flame propagation throughout periods of low fuel feeds and permits low fuel feeds at low air fiows or low power conditions, and also at high air flows as on engine deceleration, without burner failure. Purely. by way of example, it may be desired to meter to the burner nozzle 1.2 pounds of fuel per hour at minimum air fiows or low power conditions and up .to 26.3 pounds of fuel per hour at maximum air flows or full power conditions. A spray of 1.2 pounds per hour will produce a rather sensitive flame which can be quickly snuffed out by the sudden injection of air above a certain velocity, or by an oversupply of air within the region of the flame. By suitably calibrating the air inlet and bafile orifices, the velocity of the air flowing into the combustion chamber may be adjusted with respect to a pl'urality of combustion zones to insure proper or eflicient flame propagation at all air flows or power conditions. Thus the velocity within the central burner zone in the immediate region of the nozzle 26 may be held within a relatively low wall at by means of a wall 5|.

range, for example, of from 9 to 30 feet per second, the velocity within the intermediate zone from 18 to 60 feet per second, and within the outer zone from 2'! to feet per second. The total inlet capacity of all the openings which determine the respective zones should be such as to give the proper amount of air at full power conditions for efficient combustion with, for example, 6 pounds of fuel per hour. The air flowing through the ports 9 may be moving at a velocity of say 36 to feet or more per second. In order to more effectively diffuse the air as it passes into the burner chamber, suitable bafiie material such as steel wool or the like, indicated at 21, may be disposed in the chambers 2i and 22, and also in the outer chamber 26 if desired.

Figures 2 and 3 illustrate a burner of modified construction with respect to Figure l, the burner being illustrated as one of any number of similar burners mounted within the chamber 5 defined by the annular concentric walls 6 and "I in the same manner as in Figure 1. The burner of Figures 2 and 3 comprises an outer shell 40 formed with a series of high velocity air inlet holes 4|, 42 and 42' outwardly from the breech portion thereof. Within the outer shell 40 is mounted a breech assembly comprising an outer, generally cylindrical member 43 formed with circumferential rings or bosses 44 and 45' by means of which it may be suitably secured to the shell 40 as by welding or in any other suitable manner. An annular inwardly or convergingly curved wall 45 forms an extension of the member 43, and another substantially straight cylindrical wall 46 extends forwardly-from the wall 45 and is connected thereto by web portions or openwor structure defining openings 41.

The cylindrical wall 45 soon becomes heated to a high temperature after the burner starts, since it lies in the low flame area, and thereafter it furnishes a hot vaporizing surface against which spray from the nozzle 69 impinges. Among other advantages, this reduces the tendency toward collection of unburnt fuel in the breech area at low fuel delivery pressures and subsequent explosion and dangerously high heat conditions when the fuel delivery is increased. The openings '47 facilitate access of hot gases to the exterior surface of the wall 46.

- An inner breech unit, generally indicated at 48, is provided and comprises an end wall 48 from the periphery of which a converging or radially-inwardly curved wall 49 projects and is joinedat its inner edge to a straight cylindrical The walls 49, 50, 5| and adjacent part of the wall 48' form the boundary of a chamber 52; and the end wall 48' is formed with a plurality of calibrated air-inlet openings 53 for admitting controlled quantities of air to thechamber 52, and from this chamber air maypass into the nozzle area of the breech chamber at a reduced velocity through ca1i-' brated holes 54 and 55, the aggregate area of holes 54 and 55 being greater than the aggregate area of the holes 53.

Between the outer cylindrical member 43: and.

velocity of the air'passing' into the breech chamber immediately forwardly of the burner nozzle.

The end wall 48' supports a spray nozzle 60 and a spark plug or other suitable ignition device 6I.

Airunder pressure moving in a direction from left to right as viewed in Figure 2 is directed into the outer chamber 5 and passes beyond the breech portion of the burner to the holes 4|, 42,

42' and is fed into the burner chamber at this point at a relatively high velocity of say 215 feet per second; and at the same time air is fed into the annular slots 51, 58 and passes into the breech portion of the burner through the expanding chambers 51 and 58' which tend to reduce the velocity of and diffuse the air as it enters the breech chamber. Thus the velocity of the air entering through the outer passage 51 might be forty feet per second, while the air entering through the inner pasage might have a velocity of fifteen feet per second. The inlet slots 51, 58 and the chambers 51, 58' may be calibrated to provide the required amount of air at predeterminedvelocities to obtain the most efficient combustion and flame propagation within the breech area of the burner chamber without danger of blowing out the fiame at the burnernozzle during low fuelfeeds and high air flows.

'The holes 53 admit air into the chamber 52 from which it passes at a reduced velocity through the calibrated holes 54 and 55 and is projected onto the tip of nozzle 60 and also on the exposed outer surface of the spark plug 6|. This controlled supply of air tends to reduce carbon formation by furnishing sufficient oxygen to this region for admixture with the fine mist of oil, usually present in this area, to support combustion, or burn the oil without permitting it to cake on the surfaces of the nozzle and the plug.

Any convenient method of manufacture of the burner parts may be adopted. For example, the outer shell 40 may be of heat resistant sheet metal, refractory material or the like, while the outer and inner units 43 and 48 may be in the form of castings and the intermediate unit 56 of sheet metal, the parts being joined or bridged by connecting bosses and welded or otherwise secured together to form a complete assembly. Obviously other materials or methods of fabrication may be used.

Figures 4 and 5 illustrate a further modification in burner structure for carrying out the objects of the present invention. The burner as shown in Figures 4 and 5. is mounted in a chamber'5 similar to the burners of Figures 1 and 2; it comprises an outer shell 10 formed with a series of holes 1|, 1| outwardly from the breech portion of the burner, for admitting high-velocity air into the burner along the length thereof. The breech portion of the burner comprises a unit having anend wall 12, which as shown is of radially outwardly stepped construction, and projecting forwardly from theend wall are a series of concentric cylindrical walls 13, 14 and 15 which define a plurality of chambers 16 and 11, a main breech chamber '18 and a supplemental breech chamber 18'. A wall 13' surrounds the breech chamber forwardly of the nozzle, to provide .a vaporizing surface in a manner similar to the wall 46 of Fig. 2. The outer face walls of the chambers 16 and 11 are supplied with air through a plurality of openings 19 and 19', preferably arranged tangentially in order to produce a baffle effect by causing the airto pass into the chambers 1'6 and 11 to be broken up or have its velocity reduced-by circulation and frictionless This obviates the need for ber 82 which is supplied with. air through ann-ular slots 83. and holes 83'.' V

The end wall 12 may be bored or cast with holes or. suitable openings to receive a spray nozzle 84 and a spark plug 85.

Air at highvelocity entering the chamber 5 from left toright as viewed in Figure 4 is directed into. the holes 1| and 1| at for example 215 feet per second. Air also impacts the end breech wall '12 and is fed through the tangential holes 19 and 19 into the chambers 16 and 11 which action reduces the velocity of the air in the manner heretofore explained, and from these -cham-- bers the air is fed into the breech chamber 18- at a somewhat further reduced velocity through the annular series of holes 83 and 8!. example, the air entering the breech chamber through the holes 89 may be at a velocity of forty' feet per second; while the air entering the breech chamber through the holes BI may be at a velocity of fifteen feet per second. The whirling motion imparted to the air entering chambers 16 and 11 also tends to distribute the air equally through out the area of the said chambers before passing into the breech chamber 18. If desired, additional holes may be formed in the wall 15 to direct air against the tip of the nozzle 84 and the spark plug and furnish sufiicient oxygen to support combustion in the immediate region of the nozzle tip and the spark plug and thereby reduce the tendency toward carbon formation on thes parts.

While any suitable type of fuel spray nozzle '25, 60 or 84 may be used, it is preferred to use a nozzle which will operate to discharge a coneshaped spray of fuel when the latter is under low pressures in the area of lowest velocity of the incoming air, and as the fuel delivery pressure increases, the fuel spray cone will progressively lengthen and intersect the respective masses or strata of incoming air. A nozzle suitable foruse with burners of the type herein disclosed is shown in Figures 6, '1 and 8.

The nozzle illustrated in Figures 6, 7 and 8 consists of a flanged body 90 having therein av spray head 9| provided with a stem 92 encircled by a spring 93 which urges the head to seated position with th fiared tip or end portion thereof engaging in the similarly-contoured main discharge orifice or jet 94. A cap 95 is threaded on the rear extremity of the body 99, and between this cap and the body flange is a fitting 96 having a tubular portion 91 to which a fuel supply tube 98 is connected. Fuel passes into nozzle chamber 99 through ports I00; and at low pressures flows through small bores I 0 I formedin the spray head, note Figure '7, at a tangent to a central cavity or recess I02 having therein a member I03 provided with a small lowpressure discharge orifice I94. The seating tension of spring 93 is adjustable by means of thrust nut I95 and lock nut I96. The tangential arrangement of the bores I0l, causes the spray to swirl as it leaves the low pressure orifice at an angle determined by the relative areas of bores or passages NH and I04.

The tension of spring 93 may be adjusted to Between the outerv Thus, fora point where at predetermined low pressure the spray head 9| remains seated and discharge is by way of small bores NH and low pressure discharge orifice I04, but as pressure builds up, discharge is principally through the high pressure discharge orifice 94 with a certain additional discharge through orifice I04, the spray issuing at high pressures in a cone-shaped fog, the spray cone angle being determined by the angle of the cone-shaped head 9!. Thus at low fuel pressures when the air is likewise at its lowest pressure, the velocity of the fuel is steppedup by the small bores l0! and small jet I04, while at higher pressures, the outer cone-shaped discharge orifice takes over, producing a welldifiused spray in all directions. The adjustability of the spray head permits accurate synchronization of an entire set of burner nozzles.

As heretofore noted, burners of the type with which the present invention is primarily concerned are subject to a building up of reverberations, particularly at high air flows and rich fuel air ratios, which may reach an intensity such as to cause the burner flame to become extremely unstable and finally fail entirely; it is characterized by an irregular exhaust sound accompanied by an irregular flame length and a strong odor of unburnt fuel. In the burner disclosed herein, any or allof the breech chambers 20, 2| and 22 of Figure 1, 52 of Figure 2, or 16 and 11 of Figure 4, may have an individual resonance frequency which is variable in direct relation to the volume of the resonance chamber and the area of its air-inlet and discharge ports,

and since these chambers have a resonance fre-- quency different from that of the main burner chamber or tube at a given air flow and fuel feed, their resonance frequencies tend to neutralize or dampen out the reverberations of the main burner chamber. Such resonance chamber, while preferably having air-inlet and discharge ports, need only have the latter ports, or need only be in communication with the breech or main burner chamber to function as a reverberation dampener.

It will be understood that the drawings are simply illustrative, and that certain changes in construction, design and arrangement of th respective parts fall within the scope of the invention as defined by the appended claims.

I claim:

1. In a generator for heating and expanding air flowing thereto under pressure, an outer shell defining an elongated combustion chamber provided with a fuel-discharge nozzle at one nd thereof, an end wall mounting said nozzl and having a series of calibrated air-inlet orifices of varying flow capacity arranged in generally annular formation with the orifices of lowest flow capacity located centrally of said wall and the remaining orifices progressively increasing in capacity as they approach the periphery of the wall, a plurality of spaced annuli projecting forwardly from said end Wall to provide flow passages for the air admitted through said orifices and at their inner ends terminating in spaced stepped relation with the shortest annulus surrounding said nozzle, and bafiles coacting with said annuli and adapted to reduce the velocity of the air flowing into the combustion chamber in the region of the nozzle through said calibrated air-inlet orifices.

In a generator for heating and expanding air flowing thereto under pressure, an outer shell defining an elongated generally cylindrical combustion chamber provided with an end wall mounting a fuel-discharge nozzle, said end wall being provided with a series of calibrated airinlet orifices of varying area or flow capacity with the orifices of lowest flow capacity surrounding the nozzle and the remaining orifices progressively increasing in area as they approach the periphery of the wall, a plurality of substantially cylindrical walls projecting from said end wall and arranged in spaced substantially concentric formation and at their inner ends terminating in stepped relation with the shortest annulus surrounding the nozzle, said annuli separating the inlet or breech end of the combustion chamber into a plurality of sub-chambers which tend to equalize the air flowin in through said air-inlet orifices, and baflie means coactlng with said latter chambers constructed and arranged to direct the air into the combustion chamber in masses of reduced and varying velocities with the mass of lowest velocity in the immediate leg of the nozzle.

3. In a generator or burner for heating and expanding air flowing thereto under pressure, an outer shell defining a combustion chamber having a breech portion at one extremity thereof, a breech unit at the air-inlet end of said breech portion provided with an end wall formed with a plurality of radially spaced air-inlet openings, a series of radially-inwardly converging substantially cylindrical radially-spaced walls projecting forwardly from said openings and defining a plurality of air passages of gradually increasing cross-sectional area adapted to direct air into the breech portion of the combustion chamber, said passages receiving air from said inlet openings and producing an expansion efiect on the air as it flows therethrough to 'reduce the velocity thereof and diffuse the air as it passes into the said breech portion.

4. In a generator or burner for heating and expanding air flowing thereto under pressure, an outer substantially cylindrical shell defining a combustion chamber having an air inlet or breech portion at one extremity thereof, a breech unit at the air inlet end of said chamber made up of a series of outer substantially concentric cylinders and a central member having an end wall mounting a fuel spray nozzle, said outer I cylinders having their rear edges lying in the plane of said end wall and arranged in radiallyspaced relation to provide air-inlet openings, the walls of said cylinders projecting forwardly from said openings in axially converging formation and in progressively-increasing radially-spaced relation to define air inlet passages tending to expand the air entering the breech portion of the combustion chamber and reduce the velocity 5. In a generator or burner for heating and expanding air flowing thereto under pressure, an outer substantially cylindrical shell defining a main combustion chamber having a breech portion at the air-inlet extremity thereof, a breech unit for controlling the supply of air to said chamber including an outer substantially cylindrical wall projecting forwardly in radiallyinwardly-curved formation into said breech portion, another substantially similarly shaped cylindrical wall arranged concentrically within said first-named cylindrical wall, said walls projecting forwardly in progressively radially-spaced relation to define a series of air-inlet passages of gradually increasing cross-sectional area which tend to expand the air and reduce the velocity thereof as it flows into the breech portion of the combustion chamber.

6. In a generator or burner for heating and expanding air flowing thereto under pressure, an outer shell defining a main combustion chamber having a breech portion at one extremity thereof, an end wall overlying the air-inlet end of said breech portion, a fuel spray nozzle located in said breech portion, a plurality of radially-spaced walls projecting forwardly from said end wall into said breech portion and defining a plurality of air chambers therebetween in restricted communication with said breech portion, a series of tangentially-disposed air-inlet passages for admitting air to said air chambers in a manner such as to produce a baflle effect on the air and at the same time facilitate distribution of the air in said latter chambers.

7. In a generator or burner for heating and expanding air flowing thereto under pressure, an outer substantially cylindrical shell defining a main combustion chamber having a breech portion at one extremity thereof, a breech unit mounted in the air inlet end of said shell and comprising an end wall lying in a plane generally normal to the axis of said combustion 10 chamber and a plurality of substantially cylindrical radially-spaced walls projecting forwardly from said end wall into said breech portion, said cylindrical walls defining a plurality of air chambers surrounding said breech portion and in restricted flow communication therewith, said end wall being provided with a series of tangentiallydisposed air-inlet holes for communicating air to said air chambers and at the same time produce a baiile effect on the air and facilitate distribution thereof in said latter chambers, said shell being formed with a series of air inlet openings forwardly of said breech portion.

FRANK C. MOCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,370,486 Reid Mar. 1921 1,458,378 Astrom June'12, 1923 1,654,403 Blake Dec. 2'7, 1927 1,990,695 Jerome -1 Feb. 12, 1935 2,000,733 Avery May 7,1935 2,117,270 Bloom May 17, 1938 2, 67,183 Naab July 25, 1939 2,194,081 Bock Mar. 19, 1940 2,240,161 Mueller Apr. 29, 1941 2,242,797 Lucke May 20, 1941 2,247,768 Huwyler July 1, 1941 2,404,395 Milliken July 23, 1946 2,411,181 Altorfer Nov. 19, 1946 2,488,218 McCollum Nov. 15, 1949

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