US3800527A

US3800527A - Piloted flameholder construction

Info

Publication number: US3800527A
Application number: US00125882A
Authority: US
Inventors: R Marshall; D Sullivan
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1971-03-18
Filing date: 1971-03-18
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

A piloted flameholder construction having a plurality of combustion zones to which are supplied fuel and air to support combustion therewith. Combustion gases from at least one of the combustion zones are then supplied to a plurality of flameholders thereby improving combustion efficiency and stability of the flameholders. This flameholder construction is particularly adaptable for use in a ducted fan gas turbine engine. This application is reported as a Subject Invention under Government contract AF33(657)14903.

Description

United States Patent 1 1 Marshall et al. Apr. 2, 1974 [5 PILOTED FLAMEHOLDER 3,274,776 9/1966 Ravel 60/39.72 R

CONSTRUCTION [75] Inventors: Richard L. Marshall; Dennis J. Primary Examiner-Samuel Feinberg Sullivan, both of Manchester, Conn. Attorney, Agent, or Firm-Jack N. McCarthy [73] Assignee: United Aircraft Corporation, East Hartford, Conn. [57] ABSTRACT [22] Filed: Mar. 18, 1971 [21] APPL NO: 125,882 A piloted flameholder construction having a plurality of combustion zones to which are supplied fuel and air Related Application Data to support combustion therewith. Combustion gases [63] Continuation-impart of Ser. No. 741,159, June 27, from at least one of the combustion zones are then 1968, abandoned. supplied to a plurality of flame-holders thereby improving combustion efficiency and stability of the [52] [1.8. CI. 60/39.72, 60/224 flameholders. This flameholder construction is pani [51] Int. Cl. F02g 1/00 ularly adaptable for use in a ducted fan gas turbine en- [58] Field of Search 60/39.72, 39.74, 261, 39.65 gine.

, This application is reported as a Subject Invention [56] References C'ted under Government contract AF33(657) 14903.

,UNITED STATES PATENTS 2,679,137 5/1954 Robert 60/39.65 13 Claims, 5 Drawing Figures PILOTED FLAMEI-IOLDER CONSTRUCTION CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Application Ser. No. 741,159 filed June 27, 1968 for PI- LOTED FLAMEI-IOLDER CONSTRUCTION, now

abandoned.

BACKGROUND OF THE INVENTION This invention relates to a piloted flameholder construction, one configuration thereof being particularly adapted for adding heat to the bypass air of a fan engine thereby increasing the overall thrust of the engine.

In a conventional turbojet gas turbine, air passes through an aligned compressor, burner and turbine and is then discharged to atmosphere through an exhaust outlet to generate thrust. Generally, a ducted'fan engine adds the feature of taking a portion of engine air from a fan stage preceeding the low compressor and discharging it to atmosphere to generate thrust other than through the previously mentioned exhaust outlet. In the conventional ducted fan engine, this additional duct is of circular cross section and overlaps the engine to form an annular air passage therebetween. With the advent of higher thrust engines, interest has been generated in achieving a fan duct burner with performance characteristics satisfying requirements as regards combustion efficiency, operating range, high altitude operation, lean ignition properties and pressure loss.

Normally, the inlet conditions of a duct burner are such that a duct burner encounters the relatively low air temperature of a main combustion burner and the relatively high Mach number flow of an afterburner. As a'result, the requirements of a burner located in a bypass duct'cannot be satisfied by using a conventional main burner or afterburner. In this type application a conventional afterburner system lacks the stability required for operation at relatively low inlet temperatures, the wide fuel air ratio range required, and the ability to propagate the flame across the entire duct without resultant adverse effects on combustion efficiency. A conventional main burner would suffer prohibitively high pressure losses in addition to having the disadvantages of the afterburner system.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide a piloted flameholder construction which is primarily adaptable for use in a ducted fan engine, the construction having favorable stability characteristics at relatively low inlet operating temperatures and pressures; capability of operating over a wide fuel air ratio range and low pressure loss; and improved flame propagation through the flameholders extending across the entire duct.

In a preferred arrangement of the present invention a plurality of combustion zones are employed. These combustion zones are normally annular and increase in cross-sectional area in a downstream direction. As herein illustrated, each of the combustion zones includes fuel supply means, air supply means and a pair of annular radially spaced walls, combustion normally occuring therebetween. In the present embodiment the gases of combustion from the first or pilot zone progress downstream to the next combustion zone, where additional air and fuel are added to intensify the temperature of the gases coming from the pilot or initial combustion zone, the gases generated by these zones being used with a plurality of flameholders hereinafter described.

In a preferred embodiment of the present invention, ram chutes are located at the sides of the second combustion zone. These ram chutes direct air which has flowed or bypassed the pilot combustion zone into the second combustion zone. The purpose of these chutes is to insure mixing of the second zone fuel and air mixture with the pilot zone combustion gases. It should be understood that as many combustion zones as desired may be employed, each zone being of substantially the same construction and including fuel supply means, air supply means, radially spaced annular walls and ram chute mixing means.

Positioned downstream of the pilot combustion zone, and downstream of the second combustion zone as herein illustrated, is a plurality of gutter-shaped flameholders. These flame-holders are positioned around the circumference of the duct and are supported from the radially spaced annular walls. The flame-holders are supported from the walls such that the inner annular wall supports the inwardly extending flameholders and the outer annular wall supports the outwardly extending flameholders, the flameholders thereby extending substantially across the entire duct. The construction of the flameholder and the attachment to the walls is novel in that at the point of attachment the walls are slotted thereby permitting the hot combustion gases from within the combustion zone annular walls to flow out and around the flameholders. The outward flow of these gases greatly increases the stability and combustion efficiency of the flame-holders. A further embodiment of the construction of the present invention is to position a plurality of heat shields forwardly or upstream of each of the flameholders. Each of the heat shields is of substantially the same shape as the flameholders and effectively forms a double-walled flameholder construction. Since the heat shields are spaced axially from the flameholders, a passageway therebetween is formed. This passageway is in communication with a combustion zone through the aforementioned slots in the walls, and thereby provides a means for preheating each of the flameholders. More specifically, the hot combustion gases heat the shield affording initial vaporization of fuel supplied to the flameholders from an upstream fuel supply means. Additionally, the temperature of the inner flameholders is raised; these raised temperatures also contributing to flame-holder stability and efficiency.

The construction of the present invention further provides for increased stability and flameholder efficiency by providing a plurality of transfer channels extending from the pilot combustion zone to the annular walls supporting the flameholders at a point upstream of the flameholders. The exits of these transfer channels are positioned around the circumference of the duct such that each exit is in substantial axial alignment with each flameholder. Therefore, hot gases are led by the transfer channels and issued therefrom as hot streaks over the end location of each of the flameholders with the hot gases flowing onto each of the flameholders from within the duct. This type construction has been found to permit favorable flameholder stability and efiiciency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the flameholder construction in longitudinal cross section.

FIG. 2 is a longitudinal cross section of the flameholder construction.

FIG. 3 is a view taken along the line 3-3 of FIG. 2.

FIG. 4 is an enlarged view of a portion of FIG. 2. showing the positioning of a channel and flameholder along with a general flow path.

FIG. 5 is an enlarged perspective view of a portion of the invention showing the positioning of the channel with respect to its cooperating flameholder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, the construction of the present invention is clearly illustrated. As shown, the construction includes three combustion zones, the first combustion zone being pilot combustion zone 30 and includes any conventional fuel supply means 12 in the burner inlet section locatedupstream of the pilot combustion zone 30. Additionally, the inlet section 10 includes a pair-of annular radially spaced

walls

14 and 16, wall 14 constituting the inner annular wall and wall 16 constituting the outer annular wall.

Walls

14 and 16 are arranged such that at their leading edges the radial spacing therebetween is relatively small so that the air flowing into inlet section 10 is only a small percentage of the total airflow, the remainder of the air flowing around the outer surfaces of

walls

14 and 16.

Positioned in the radial space between

walls

14 and 16 and in the burner inlet section 10 is fuel supply means 12. As illustrated, the pilot combustion zone 30 is formed by a pilot body 18 which is supported from

walls

14 and 16 and includes a nose portion 20 at its leading edge. As a result of the shape of the leading edge of the pilot body 18 and the pilot nose 20, combustion within the pilot zone occurs in a protected region. Also pilot body 18 includes two radially spaced walls 22 and 24, each wall having a plurality of openings 26.

It is through these latter openings 26 that a pre-mixed fuel-air mixture passes from the inlet section 10 into pilot zone 30, these openings are the primary means of metering the airflow to the pilot zone 30. After being burned in the pilot zone 30 these hot gases flow downstream into the second zone 40. Combustion zone 40 is constructed in much the same manner as pilot combustion zone 30 in that it includes fuel supply means 32 positioned downstream of pilot zone 30 and surrounding the

walls

14 and 16 respectively. Combustion zone 40 as pilot zone 30 also includes a pair of annular radially spaced

walls

34 and 36.

The

walls

34 and 36 are arranged such that wall 34 is the inner annular wall of combustion zone 40, the leading portion 35 thereof overlapping the downstream portion 15 of inner wall 14 of pilot zone 30. Similarly, wall 36 is the outer annular wall of zone 40 and its leading portion 37 overlaps the downstream portion 17 of wall 16. In each instance portion 35 is spaced radially from portion 15 and portion 37 from portion 17 so that two annuli exist between the pilot combustion zone 30 and the second combustion zone 40. Within each annulus is positioned a plurality of scoops 41, each of the scoops facing forwardly to receive air which has flowed around the inlet. As shown, fuel supply means 32 are positioned at the inlet of each of the scoops, it therefore being clear that scoops 41 insure a proper mixing of the incoming fuel and air mixture with the combustion gases exiting from the pilot zone 30. To insure this proper mixing the exists 42 of the scoops 41 are arranged such that they face either inwardly or outwardly. In the construction illustrated herein, the inwardly facing exits are attached and supported from the outer annular wall 36 and the outwardly facing exits are attached and supported from the inner annular wall 34. With respect to the combustion zone 40, the scoops all face inwardly thereto. To further enhance mixing, either short scoops 41A or long scoops 418 may be employed, this being more clearly illustrated in FIG. 3. It should be noted that either all long, all short, or any combination thereof may be used.

Downstream of combustion zone 40 is the third combustion zone 52. Combustion zone 52 includes fuel supply means 54 and also a plurality of flameholders 56. Flameholders 56 are positioned downstream of fuel supply means 54, and are supported from the annular walls comprising the second combustion zone 40 at the downstream ends of these walls. The flameholders 56 are arranged such that they extend radially from

walls

34 and 36, the flameholders supported from inner annular wall 34 extending radially inward while the flameholders supported from the outer annular wall 36 extending radially outward. The flameholder supports may be rods or any other type of fixture desired. With this type arrangement it is possible to realize stable burning across an entire duct or opening. This can more clearly be seen in FIG. 2.

To improve the stability and the combustion efficiency of the flameholders the present invention provides a number of unique features. As illustrated in the present embodiment, gases from the pilot zone 30 move downstream and are mixed with the air and fuel entering the second combustion zone 40 the heat and temper thereby being intensified. To utilize these hot combustion gases which have been generated in the first two combustion zones, the

annular walls

34 and 36 are slotted around their entire circumference, as at 60 to permit passage of these gases to the flame-holders 56. In the present embodiment flameholders 56, which are gutter-type flameholders which are substantially U- shaped in cross section with the apex of the U facing upstream, are positioned over slots 60 such that the generated combustion gases may pass along and radially out the upstream and downstream sides of the flameholders 56. A flameholder support could include integral fingers projecting from its open end of the U to its flameholder. To further enhance the performance characteristics of the flame-holders 56, a plurality of heat shields 62 positioned forwardly of and axially spaced from each of the flameholders 56 may be employed. Each of the heat shields 62 is substantially the same shape as its associated flameholder, so effectively the construction is a double-walled construction with a passageway 64 therebetween.

FIG. 3 illustrates an additional feature which also improves the performance characteristics of flameholders 56. A plurality of transfer channels 66 are employed, one end 68 of each of the channels being in communication with the gases generated in the two combustion zones and each of the other ends 70 being arranged around the circumference of

annular walls

34 and 36. These transfer channels are located between the downstream portion l5 of inner wall 14 and the leading edge portion 35 of wall 34 and between the downstream portion 17 of wall 16 and the leading portion 37 of wall 36. The ends 68 of the channels 66 can be considered the inlet ends of the channels and the ends 70 of the channels can be considered the exit ends of the channels, in that gases generated flow outwardly from end 68 to end 70 to the inside of

walls

34 and 36 where they then flow downstream. The exits 70 of transfer channels 66 are further arranged such that each exit 70 is substantially axially aligned with each of the flameholders 56. Therefore, as the hot combustion gases issued from the exits 70, they do so as hot streaks which travel along

walls

34 and 36 and onto each of the flameholders 56.

in FIG. 2 the present invention is illustrated as being positioned in an annular duct 80, concentric wall 72 being the inner wall of duct 80 and concentric wall 74 being the outer wall of duct 80. Each wall has similar flange means 76 for attachment to an engine (not shown).

it is to be understood that the invention is not limited to the specific embodiments herein illustrated and described but may be used in other ways without departure from its spirit as defined by the following claims.

We claim:

1. A piloted flameholder construction including a plurality of combustion zones, each zone having means for supplying fuel and air thereto for combustion, wherein the improvement comprises:

supporting a plurality of flameholders rearwardly of at least the first combustion zone; and

means for supplying hot combustion gases from at least one of the combustion zones to apoint forwardly of each of the flameholders, each of these points being in substantially axial alignment with each of the flameholders, the combustion gases exiting from each of these points as a hot streak and being directed at and onto each of the flameholders.

2. A flameholder construction as in claim 1, wherein:

and the flameholders extend radially inwardly and outwardly from these walls. 3. A flameholder construction as in claim 2, wherein:

the means for supplying hot combustion gases includes a plurality of transfer channels extending from at least one combustion zone to a point forwardly of the flameholders, each of the channels having an exit which is substantially axially aligned with a flameholder.

4. A piloted flameholder construction including a plurality of combustion zones, each zone having means for supplying fuel and air thereto for supporting combustion at each zone, wherein the improvement comprises:

a first combustion zone including a first pair of radially spaced annular walls, the upstream ends of the spaced walls constituting the burner system inlet,

this first combustion zone including a protected region bounded by a second pair of radially spaced annular walls inside the first pair of walls, means for permitting a predetermined amount of air to pass into this pilot combustion zone, the remainder of the airflow passing around the inlet of the burner system;

a second combustion zone downstream of the first combustion zone including a third pair of radially spaced annular walls, the third pair of annular walls being radially spaced from the first pair of walls;

a plurality of scoops positioned between the two pairs of annular walls, each of the scoops having exit locations directed either inwardly or outwardly, the inlets of the scoops facing forwardly to receive the air flowing past the first combustion zone;

a plurality of transfer channels extending between the first combustion zone and the second combustion zone, the transfer chennels permitting passage of hot combustion gases from the first combustion zone to the exit of each of the transfer channels; and

a third combustion zone downstream of the second combustion zone including a plurality of guttershaped flameholders, each of the flameholders being substantially in axial alignment and downstream thereof of the exits of each of the transfer channels, a hot gas streak issuing from the exit of each of the transfer channels and being directed at each of the flameholders.

5. A flameholder construction as in claim 4 wherein:

the third pair of walls support the flameholders, the walls being slotted at the point of support of each of the flameholders to permit passage of hot combustion gases from the second combustion zone along each of the flameholders.

6. A flameholder construction as in claim 5 wherein:

a plurality of heat shields of substantially the same cross section as each of the flameholders is spaced axially therefrom and at the leading edge of each of the flameholders, the hot combustion gases from the second combustion zone being passed through the slots between each of the heat shields and flameholders and around the flameholders.

7. A flameholder construction as in claim 6 wherein:

the heat shields and the flameholders are substantially U-shaped, and the apex of the U of the heat shield and flameholder is facing upsteam.

8. A flameholder construction as in claim 5 wherein:

the flameholders supported from the inner annular wall extend radially inward therefrom and the flameholders supported from the outer annular wall extend radially outward therefrom.

9. A piloted flameholder construction for use with a ducted fan gas turbine engine, the flameholder being positioned in the relatively cool fan gas stream and including a plurality of combustion zones, each of the zones having means for supplying fuel and air thereto for supporting combustion in each zone, wherein the improvement comprises:

an outer concentric wall including means for connecting the wall to the engine;

an inner concentric wall spaced radially inward one of the combustion zones also including a pair of annular radially spaced walls, the flameholders being supported from both of the walls, the flameholders extending radially inwardly and outwardly from the wall thereby extending substantially across the entire duct; and

means for supplying hot combustion gases from at least one of the combustion zones to a point forwardly of each of the flameholders, each of these points being in substantially axial alignment with each of the flameholders, the combustion gases exiting from each of these points as a hot streak and being directed at and onto the base of each of the flameholders.

10. A flameholder construction as in claim 9 wherein:

there are three combustion zones and the flameholders are positioned downstream of the second combustion zone and the third combustion zone includes means for conducting hot combustion gases around each of the flameholders thereby heating each of the flameholders.

l l. A piloted flameholder construction as in claim 10 5 wherein:

each of the flameholders are gutter-shaped and a heat shield of substantially the same construction is positioned forwardly of each of the flameholders, each of the heat shields and flameholders thereby having a space therebetween, this space being in communication with one of the preceeding combustion zones thereby permitting a flow of hot combustion gases between the heat shields and the flameholders.

12. A piloted flameholder as in claim 11 wherein:

the heat shields and the flameholders are substantially Ushaped, and the apex of the U of the heat shield and flameholder is facing upstream.

13. A piloted flameholder construction as in claim 10 wherein:

the means for supplying the hot combustion gases includes a plurality of transfer channels each of the channels extending from the second combustion zone to a point forwardly of each of the flameholders.

Claims

1. A piloted flameholder construction including a plurality of combustion zones, each zone having means for supplying fuel and air thereto for combustion, wherein the improvement comprises: supporting a plurality of flameholdErs rearwardly of at least the first combustion zone; and means for supplying hot combustion gases from at least one of the combustion zones to a point forwardly of each of the flameholders, each of these points being in substantially axial alignment with each of the flameholders, the combustion gases exiting from each of these points as a hot streak and being directed at and onto each of the flameholders.

2. A flameholder construction as in claim 1, wherein: the combustion zones include a pair of annular radially spaced walls each of the flameholders being supported from at least one of these pairs of walls, and the flameholders extend radially inwardly and outwardly from these walls.

3. A flameholder construction as in claim 2, wherein: the means for supplying hot combustion gases includes a plurality of transfer channels extending from at least one combustion zone to a point forwardly of the flameholders, each of the channels having an exit which is substantially axially aligned with a flameholder.

4. A piloted flameholder construction including a plurality of combustion zones, each zone having means for supplying fuel and air thereto for supporting combustion at each zone, wherein the improvement comprises: a first combustion zone including a first pair of radially spaced annular walls, the upstream ends of the spaced walls constituting the burner system inlet, this first combustion zone including a protected region bounded by a second pair of radially spaced annular walls inside the first pair of walls, means for permitting a predetermined amount of air to pass into this pilot combustion zone, the remainder of the airflow passing around the inlet of the burner system; a second combustion zone downstream of the first combustion zone including a third pair of radially spaced annular walls, the third pair of annular walls being radially spaced from the first pair of walls; a plurality of scoops positioned between the two pairs of annular walls, each of the scoops having exit locations directed either inwardly or outwardly, the inlets of the scoops facing forwardly to receive the air flowing past the first combustion zone; a plurality of transfer channels extending between the first combustion zone and the second combustion zone, the transfer chennels permitting passage of hot combustion gases from the first combustion zone to the exit of each of the transfer channels; and a third combustion zone downstream of the second combustion zone including a plurality of gutter-shaped flameholders, each of the flameholders being substantially in axial alignment and downstream thereof of the exits of each of the transfer channels, a hot gas streak issuing from the exit of each of the transfer channels and being directed at each of the flameholders.

5. A flameholder construction as in claim 4 wherein: the third pair of walls support the flameholders, the walls being slotted at the point of support of each of the flameholders to permit passage of hot combustion gases from the second combustion zone along each of the flameholders.

6. A flameholder construction as in claim 5 wherein: a plurality of heat shields of substantially the same cross section as each of the flameholders is spaced axially therefrom and at the leading edge of each of the flameholders, the hot combustion gases from the second combustion zone being passed through the slots between each of the heat shields and flameholders and around the flameholders.

7. A flameholder construction as in claim 6 wherein: the heat shields and the flameholders are substantially U-shaped, and the apex of the U of the heat shield and flameholder is facing upsteam.

8. A flameholder construction as in claim 5 wherein: the flameholders supported from the inner annular wall extend radially inward therefrom and the flameholders supported from the outer annular wall extend radially outward therefrom.

9. A piloted flameholder construction for use with a ducted fan gas turbine engine, the flameholder being positioned in the relatively cool fan gas stream and including a plurality of combustion zones, each of the zones having means for supplying fuel and air thereto for supporting combustion in each zone, wherein the improvement comprises: an outer concentric wall including means for connecting the wall to the engine; an inner concentric wall spaced radially inward therefrom and also including means for connecting the wall to the engine, the two walls forming a duct therebetween within which the plurality of combustion zones are positioned, the combustion zones being arranged so that each successive downstream zone can accommodate a greater amount of flow than the zone immediately upstream; one of the combustion zones also including a pair of annular radially spaced walls, the flameholders being supported from both of the walls, the flameholders extending radially inwardly and outwardly from the wall thereby extending substantially across the entire duct; and means for supplying hot combustion gases from at least one of the combustion zones to a point forwardly of each of the flameholders, each of these points being in substantially axial alignment with each of the flameholders, the combustion gases exiting from each of these points as a hot streak and being directed at and onto the base of each of the flameholders.

10. A flameholder construction as in claim 9 wherein: there are three combustion zones and the flameholders are positioned downstream of the second combustion zone and the third combustion zone includes means for conducting hot combustion gases around each of the flameholders thereby heating each of the flameholders.

11. A piloted flameholder construction as in claim 10 wherein: each of the flameholders are gutter-shaped and a heat shield of substantially the same construction is positioned forwardly of each of the flameholders, each of the heat shields and flameholders thereby having a space therebetween, this space being in communication with one of the preceeding combustion zones thereby permitting a flow of hot combustion gases between the heat shields and the flameholders.

12. A piloted flameholder as in claim 11 wherein: the heat shields and the flameholders are substantially U-shaped, and the apex of the U of the heat shield and flameholder is facing upstream.

13. A piloted flameholder construction as in claim 10 wherein: the means for supplying the hot combustion gases includes a plurality of transfer channels each of the channels extending from the second combustion zone to a point forwardly of each of the flameholders.