Air preheating combustion apparatus

Abstract

A low emission combustion apparatus for a gas turbine engine employs vaporization of liquid hydrocarbon fuel to produce a mixture of vaporized fuel and primary or combustion air for a main combustion apparatus. The primary air is brought to a high enough temperature for vaporization of fuel by an air preheating combustor in which a relatively small part of the total fuel is burned. The preheating combustor operates at a relatively low temperature to avoid production of nitrogen oxides, and thus may produce some carbon monoxide. This, however, is burned in the main reaction zone, which operates at a higher temperature. Prevaporization of the fuel eliminates hot spots caused by fuel droplet combustion and thus promotes clean combustion. The fuel vaporizer comprises structure defining two concentric annular passages through which the air flows with swirl and in which the fuel is laid on the outer wall of each passage from a circumferential manifold. Fuel may be supplied to one or both manifolds.

Description

My invention is directed to combustion apparatus of a type suitable for use in gas turbine engines and particularly to a combustion apparatus employing combustion of a minor part of the fuel in a precombustor which brings all of the primary or combustion air for the main combustor to a temperature high enough for successful vaporization of fuel delivered into it within a fuel vaporizer through which the primary air proceeds to a main reaction zone where the major part of the fuel is burned.

The combustion apparatus according to the invention is particularly intended for use with engines of a non-regenerative type in which the combustion air is at whatever temperature results from the compression of the air, without additional heating in a regenerator or recuperator by exhaust gases.

It is well known that a great deal of effort has been put into devising combustion apparatus for power plants of all sorts to produce exhaust gases with extremely low concentrations of products considered to be inimical to public health such as smoke, unburned hydrocarbons, carbon monoxide, and oxides of nitrogen. One promising avenue toward such clean combustion lies in vaporization of the liquid hydrocarbon fuel and mixture of the vapor with the combustion air prior to the actual combustion of the fuel in the air. This is relatively easy in an engine of a regenerative type in which the air entering the combustion apparatus is ordinarily at about 500.degree. to 600.degree.C. However, my invention is directed to cleaning the exhaust of a known type of non-regenerative single-shaft gas turbine engine, the Allison Model 501 engine. This engine, in various models, is used for aircraft propulsion, in stationary power plants for gas pumping and generation of electricity, and for propulsion of boats. A typical Model 501 engine has a power output of 4680 shaft horsepower under static sea level conditions and 1084.degree.C. turbine inlet temperature. The engine has a compression ratio of 9.2 to 1.

Fuel is burned in six combustion liners arranged in parallel relation in an annular combustion air space to which air is delivered by the compressor. The general arrangement of combustion liners in the engine is as shown in McDowall et al. U.S. Pat. No. 2,729,938, Jan. 10, 1956, and Tomlinson U.S. Pat. No. 3,064,424, Nov. 20, 1962. Rated air flow is 14.65 kilograms per second or about 2.45 kilograms per second through each combustion liner.

According to my invention, the relatively low temperature compressor discharge air supplied to the combustion apparatus of the engine is heated to about 500.degree. to 650.degree.C. in an air preheating combustor associated with each main combustion liner, the air so heated flows through fuel vaporization apparatus in which fuel is vaporized and mixed with the combustion air so supplied, and the resulting mixture is burned in a main combustion zone of the apparatus. Thereafter, it flows through the dilution zone of the combustion apparatus where additional unheated compressed air is mixed with the combustion products to bring the turbine motive fluid to the desired temperature.

While the invention is described here in terms of application to a particular engine, it will be obvious that the principles of the invention may be applied to engines of various sizes and pressure ratios, and with other different parameters.

The principal objects of my invention are to provide a clean burning combustion apparatus, to provide a combustion apparatus in which air for fuel vaporization is preheated prior to vaporization of the fuel and entry of the resulting mixture into a main reaction zone; to provide improved fuel vaporization means for a combustion apparatus; and to provide a combustion apparatus which is clean burning over a relatively wide range of power outputs.

The nature of my invention and its advantages will be apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention, the accompanying drawings thereof, and the appended claims.

Referring to the drawings,

FIG. 1 is a schematic illustration of a combustion apparatus incorporating a combustion liner according to my invention.

FIG. 2 is an enlarged fragmentary sectional view taken on the plane indicated by the line 2--2 in FIG. 3.

FIG. 3 is a longitudinal sectional view of the combustion liner.

FIG. 4 is an enlargement of a portion of FIG. 3.

Referring first to FIG. 1, a combustion liner 2 according to the invention is mounted within a housing or combustion outer case 3. A compressor 4 delivers air under pressure into a space 6 defined between the housing 3 and the exterior of the combustion liner 2. Fuel is supplied to the combustion liner through a fuel line 7 connected to a fuel nozzle 8 which delivers fuel into a preheating combustor 10.

Additional fuel is supplied through lines 11 and 12 to a fuel vaporizer 14. The combustion products from the preheating combustor 10 flow through the vaporizer 14 into main combustion apparatus 15 defined by the downstream portion of the liner 2. The combustion products from the main combustion apparatus are discharged through an outlet 16 and through suitable transition ducting (not illustrated) into the turbine of the gas turbine engine, which drives the compressor 4.

Referring now to FIG. 3, the fuel atomizing nozzle 8 enters the upstream end of the preheating combustor 10 where it is surrounded by an air inlet swirler 18 which preferably is a part of the fuel nozzle assembly. The preheating combustor 10 is enclosed by a wall of circular cross section defining a dome 19 at the upstream end, a reaction zone side wall 20, and a diverging dilution and outlet section 22. The fuel vaporizer 14 begins at the downstream end of wall section 22. It is enclosed by a cylindrical wall portion 23 and a converging downstream wall portion 24 which ends at the beginning of the main combustion apparatus 15. This combustion apparatus is enclosed by an annular forward wall 26 and a side wall portion 27 which provides the outer wall of the main reaction zone 28 in which combustion of the fuel is completed. The reaction zone is connected through a slightly converging wall section 30 to a liner wall section 31 which encloses the dilution zone 32 and terminates at the outlet 16. The combustion liner may be supported at nozzle 8 by an outer swirler 34 mounted on the swirler 18 and by suitable supports at the discharge end of the liner, as is common. Suitable ignition apparatus and cross connections between combustion liners (not illustrated) may be provided generally as shown in the McDowall et al patent cited above.

The preheating combustor 10 is generally similar to conventional gas turbine combustion liners except for the fact that it is proportioned to operate on a low overall fuel-air ratio so as to discharge combustion products at about 600.degree.C., much below the inlet temperature of a gas turbine. In addition to the combustion air entering through swirlers 18 and 34, combustion air enters through a ring of six ports 35 distributed around the forward portion of wall 20. I prefer that about 40% of preheater combustion air enter through the swirlers and 60% through ports 35. Combustion takes place in the usual manner, and dilution air to mix with the combustion products is admitted through six ports 36 near the downstream end of wall section 20 and six ports 38 in the upstream end of diverging wall section 22. Air entering radially through dilution air ports 36 and 38 mixes with the combustion products from burning of the fuel discharged by nozzle 8. The combustion products then are discharged through an annular outlet 39 into the fuel vaporizer 14.

The fuel vaporizer includes a wall 40 defining with the outer wall portions 23 and 24 an annular passage 42 of approximately constant area. Wall 40 is supported from wall 23 by a ring of swirl vanes 43 which swirl the air flowing into the passage 42. Vanes 43 terminate at a sheet metal ring 44 abutting the inner surface of wall 23. The downstream end of wall 40 is welded to a wall 46 which defines the outer boundary of a second annular passage 47 of approximately constant area. A ring 48 is fixed to the upstream ends of walls 40 and 46. The inner boundary of passage 47 is defined by a converging wall 51 supported from wall 46 by a swirler 52. Swirler 52 (see also FIG. 2) comprises an annular cascade of vanes 54 extending between an outer ring 55 abutting wall 46 and an inner ring 56 abutting wall 51.

Wall 51 forms part of a centerbody 58 which, in addition to the side wall 51, has a forward wall 59 and a downstream end wall 60. The structure providing the two passages 42 and 47 through the fuel vaporizer has now been described.

Introduction of fuel is accomplished from a manifold 62 on the outer surface of wall section 23 and a manifold 63 on the outer surface of wall 46. These are connected to a source of fuel through the fuel lines 11 and 12 already referred to. Each manifold delivers fuel to the inner surface of the wall on which it is mounted through a ring of small holes which discharge onto the inner surface of the wall just downstream of the ring 44 or 55, respectively. Eighteen approximately tangential fuel holes 64 evenly spaced around the axis of the apparatus are machined through the wall 46 and 26 similar holes are machined through the wall 23. Fuel thus discharged onto the inner surfaces of the walls is contacted by the hot air coming through the swirler immediately upstream from the fuel delivery point, evaporated, and mixed with the air. It is then discharged through the downstream ends of the coaxial passages 42 and 47. The two streams merge in the outlet from the fuel vaporizer and discharge into the reaction zone 28 through the central opening 66 in wall 26. It should be noted that this opening is slightly smaller than the diameter of the discharge end of the vaporizer so that the innermost portion of the wall serves as a flow dam to promote turbulence and mixing. Due to the swirl around the liner axis, the fuel-air mixture tends to recirculate in a generally toroidal pattern in the reaction zone, and the fuel burns after being lit off by any suitable igniter.

No combustion air is added in the reaction zone. The reaction zone wall 27 is cooled by convection by structure of a type previously known. Air to cool the side wall 27 flows between the outer surface of this wall and the inner surface of a sleeve 67 which is supported adjacent the outer surface of wall 27 by axially extending strips 68 spaced circumferentially around the wall. As shown more clearly in FIG. 4, a passage 70 for convection cooling air is defined between the walls 27 and 67. This is closed at the downstream end by a ring 71 disposed between the walls, and the cooling air is discharged into the combustion liner through a ring of holes 72. A baffle 74 fixed to the wall 27 deflects this air downstream along the inner surface of the wall portion 30 for film cooling of this wall.

Dilution air is admitted to the dilution zone 32 through a ring of eight secondary air ports 76. The resulting mixture with the combustion products from the main combustion zone constitutes the motive fluid developed by the combustor.

It may be desirable to indicate typical dimensions of a combustion liner such as that shown. FIG. 3 is a drawing to scale of a liner approximately 15 centimeters in diameter. Primary ports 35 are approximately 13 millimeters in diameter, and ports 36 and 38 are approximately 20 millimeters in diameter. Fuel inlet ports 64 and the corresponding ports through wall 23 are about 4 millimeters in diameter. The fuel ports should be large enough so that the fuel may be admitted without any considerable pressure drop or without going in at high velocity.

The fabrication of the combustion apparatus may follow usual techniques with the parts being formed to shape and welded or brazed together.

Considering now the preferred mode of operation of the combustion apparatus and referring again to FIG. 1, we discuss specifically an engine operating normally at constant speed and air flow, with fuel flow varied to vary engine power output through variation of turbine inlet temperature. Fuel for the pilot or preheater fuel nozzle 8 and for the main fuel manifolds 62 and 63 may be drawn from a fuel supply line 78 by a pump 79 which may be driven by the engine. The pump delivers fuel through a fuel control 80 to an engine metered fuel line 82. Fuel control 80 determines the rate of supply of fuel to the engine and returns excess fuel through a return line 83. Metered fuel line 82 branches into the lines 7, 11, and 12 previously referred to. Division of flow between the several lines is suitably controlled. As illustrated, a valve 84 controls flow through line 7, a valve 85 controls flow through line 11, and a valve 86 controls flow through line 12. Fuel is supplied constantly to the pilot or preheat fuel nozzle 8. Valve 84 may be a flow-limiting valve limiting flow to about 30% of maximum power fuel flow. At idle (substantially zero shaft power) and power levels above that, fuel is supplied to the fuel manifold 62 through valve 85. This may be a valve responsive to the pressure ahead of valve 84 which opens at a predetermined value of this pressure and continues to open as flow increases through line 82 with increasing engine power level. The manifold 63 is fueled only at higher power levels of the engine. This flow may be controlled by a valve 86 which opens in response to increased fuel pressure level at higher fuel flow levels.

Any other suitable arrangement for sequencing or controlling flow to the manifolds may be used. Many such are known in connection with duplex fuel nozzles or with zone burning arrangements in jet engine afterburners, for example. My invention is not concerned with the details of valving or fuel supply, which may be as required to suit the operating environment of the engine. Valves such as 84, 85, and 86 may control flow to a number of combustion liners in parallel.

In the operation of the combustor, it is contemplated that about 20% of full power fuel will be injected through nozzle 8 so as to preheat the air delivered to the vaporizer to about 600.degree.C. Since a rather large amount of air is admitted through the ports 35, 36, and 38, the resulting combustion products are cool and air-rich. The combustion zone in the preheating combustor is conventional and will have hot spots, fuel droplets, and the usual deficiencies of conventional combustors. However, the NO.sub.x contribution from this zone is low due to the small amount of total fuel (20%) admitted in the preheat zone. The low combustion temperature and short residence time may cause some exhaust of carbon monoxide or unburned hydrocarbons from the preheating combustor, but these are duly oxidized in the main combustion zone 28 where temperature will rise to about 1400.degree. to 1650.degree.C. Because of combustion with a premixed mass may vaporized fuel and air, there is clean combustion, avoiding hot spots, in the main reaction zone, minimizing combination of oxygen with nitrogen. The preheating combustor does not require any variable geometry; that is, means for varying the air flow split. If found desirable, means such as are well known maay be provided to throttle flow through the main dilution air ports 76 to vary the ratio of primary to secondary air in the main combustion apparatus.

The structure, mode of operation, and advantages of combustion apparatus according to the invention should be apparent to those skilled in the art from the foregoing description.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

Claims

I claim:

1. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide at least substantially all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising means defining a passage leading from the preheating combustor to the main reaction zone, and means for delivering fuel into the said passage for evaporation and mixture with the gases flowing through the said passage; and the main dilution zone defining entrances for dilution air by-passing the preheating combustor.

2. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide at least substantially all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising means defining a passage leading from the preheating combustor to the main reaction zone and means for delivering fuel into the said passage for evaporation and mixture with the gases flowing through the said passage; the preheat dilution zone diverging downstream and the fuel vaporizer converging downstream to an outlet into the main reaction zone; the main reaction zone diverging abruptly from the fuel vaporizer outlet; and the main dilution zone defining entrances for dilution air by-passing the preheating combustor.

3. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a wall film fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising wall means defining an annular passage leading from the preheating combustor to the main reaction zone, means for imparting swirl to the gases flowing through the said passage, means for delivering fuel to the outer wall of the said passage for evaporation and mixture with the gases flowing through the said passage.

4. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a wall film fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising wall means defining an annular passage leading from the preheating combustor to the main reaction zone, means for imparting swirl to the gases flowing through the said passage, means for delivering fuel to the outer wall of the said passage for evaporation and mixture with the gases flowing through the said passage, the preheat dilution zone diverging downstream and the fuel vaporizer converging downstream to an outlet into the main reaction zone; and the main reaction zone diverging abruptly from the fuel vaporizer outlet.

5. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a wall film fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising wall means defining outer and inner annular passages leading in parallel from the preheating combustor to the main reaction zone, means for imparting swirl to the gases flowing through the said passages, means for delivering fuel to the outer walls of the said passages for evaporation and mixture with the gases flowing through the said passages, and means for routing fuel alternatively to one or both of said passages.

6. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a wall film fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising wall means defining outer and inner annular passages leading in parallel from the preheating combustor to the main reaction zone, means for imparting swirl to the gases flowing through the said passages, means for delivering fuel to the outer walls of the said passages for evaporation and mixture with the gases flowing through the said passages, and means for routing fuel alternatively to one or both of said passages; the preheat dilution zone diverging downstream and the fuel vaporizer converging downstream to an outlet into the main reaction zone; the main reaction zone diverging abruptly from the fuel vaporizer outlet.

7. A combustion apparatus for a gas turbine engine or the like comprising, in combination, a housing adapted to receive air under pressure and a combustion liner in the housing; the combustion liner having an upstream end and a downstream outlet end and defining, in flow sequence from the upstream end to the downstream end, an air preheating combustor, a wall film fuel vaporizer, a main reaction zone, and a main dilution zone; the air preheating combustor comprising a preheat reaction zone having means for admitting preheat combustion air and fuel and a preheat dilution zone having means for admitting dilution air and mixing the dilution air with the combustion air from the preheat reaction zone to provide all combustion air for the main reaction zone, in combination with means to proportion the fuel and air so as to discharge a combustion products and air mixture from the preheating combustor at approximately 600.degree. Celsius into the fuel vaporizer; the fuel vaporizer comprising wall means defining outer and inner annular passages leading in parallel from the preheating combustor to the main reaction zone, means for imparting swirl to the gases flowing through the said passages, means for delivering fuel to the outer walls of the said passages for evaporation and mixture with the gases flowing through the said passages, and means for routing fuel alternatively to one or both of said passages; the preheat dilution zone diverging downstream and the fuel vaporizer converging downstream to an outlet into the main reaction zone; the main reaction zone diverging abruptly from the fuel vaporizer outlet; means for convectively cooling the liner wall portion bounding the reaction zone by air flowing to the main dilution zone; and the main dilution zone defining entrances for dilution air by-passing the preheating combustor.

8. A method of burning liquid hydrocarbon fuel in compressed combustion air comprising burning and mixing in the air a portion of the fuel sufficient to produce a mixture of air and combustion products at about 600.degree. Celsius in a first zone; flowing the said mixture into a second zone and evaporating the remainder of the fuel in the mixture in the second zone; flowing the resulting mixture of air, combustion products, and fuel into a third zone; and completing combustion of the fuel in the air in the said resulting mixture in the third zone.

9. A method of burning liquid hydrocarbon fuel in compressed combustion air to provide motive fluid for an engine comprising burning and mixing in the air a portion of the fuel sufficient to produce a mixture of air and combustion products at about 600.degree. Celsius in a first zone; flowing the said mixture into a second zone and evaporating the remainder of the fuel in the mixture in the second zone; flowing the resulting mixture of air, combustion products, and fuel into a third zone; and completing combustion of the fuel in the air in the said resulting mixture in the third zone; flowing the resulting product into a fourth zone; and mixing dilution air with the said resulting product in the fourth zone to provide motive fluid for an engine.