US3527052A

US3527052A - Combustion system with aerodynamically variable geometry

Info

Publication number: US3527052A
Application number: US748998A
Authority: US
Inventors: William Dean Bryce
Original assignee: TECHNOLOGY UK
Current assignee: TECHNOLOGY UK
Priority date: 1967-08-10
Filing date: 1968-07-31
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08
Also published as: DE1751838C3; DE1751838A1; DE1751838B2; FR1582611A; GB1184683A

Description

. septy s; 19 70 I W.V D.'- BRYCE COMBUSTION SYSTEM-WITH AEBODYNIAIMICALLYY VARIABLE GEOMETRY Filed July 31, 1968 2 SheetS-Sheet l r s M Ma R M Ma HA u. W

' Sept. 8, 191 0. I

. Filed July 31, 1968 w. D. BRYC-E' 3,527,052 1C0MBU'STI0N SYSTEM WITH AERCDYNAMICALLY VARIABLE GEOMETRY 2 Sheets-Sheet 2 FIG. 2.

Inventor B wuu/m usnyce mm, mm, mus: 'nosus/c i ttorntys United States Patent 3,527,052 COMBUSTION SYSTEM WITH AERODYNAM- ICALLY VARIABLE GEOMETRY William Dean Bryce, Farnham, Surrey, England, as-

signor to Minister of Technology in Her Britannic Majestys Government of the United Kingdom of Great Britain and Northern Ireland, London, England Filed July 31, 1968, Ser. No. 748,998 Claims priority, application Great Britain, Aug. 10, 1967, 36,856/ 67 Int. Cl. F02c 7/00 US. Cl. 6039.65 12 Claims ABSTRACT OF THE DISCLOSURE Suction is applied to the surfaces of passages by which air enters a combustion chamber, to control the pattern of air flow in order to vary the fuel to air ratio and other conditions in the primary combustion zone. In one embodiment, a baflle in the air inlet to a combustor surrounds a spray atomiser to form an annular duct by which air passes to the primary zone. Further air passes round the outside of the baflle which is provided with suction slots in its surface. By varying the amount of suction, the direction of the further air can be altered and the volume flowing to the primary and secondary zones varied accordingly.

In another embodiment, the end wall of a flame tube surrounding the air inlet to the primary combustion zone is a hollow structure having an opening facing upstream of flow through the combustion chamber. Slots are provided in the downstream face of the end wall and around its periphery whereby air entering the opening can be directed along the face and the flame tube walls for cooling. Adjacent to the peripheral slot is an annular tube having rows of holes in its surface so that suction applied to the tube will act on the cooling air issuing from the slot to reduce its velocity and change its direction. The cooling stream normally passes over secondary air inlet holes in the flame tube walls and directs the secondary air in a generally downstream direction to give an extended recirculation pattern. Diverting the cooling stream has the effect of varying the inlet angle of the secondary air and thus reduce the length of the recirculation pattern.

The invention relates to combustion apparatus as may be used in gas turbine plant.

In conventional gas turbine plant, a compressor discharges air into a combustion system wherein fuel is introduced into the flow and burned, the combustion gases so produced being led to a turbine.

Generally, the compressor supplies more air than is necessary for complete combustion of the fuel and it is usual to divide the air flowing to the combustion system into two or more streams One of which goes to initiate and support combustion while another is used to dilute the hot combustion products to reduce their temperature to a value acceptable to the turbine.

In gas turbine engines for aircraft, combustion systems are required to operate over a wide range of conditions which involve differing ratios in the mass flows of the combustion and dilution air streams. It is therefore desirable to have means whereby the distribution of air beween these streams may be varied at will and it has been previously proposed to inject a supply of controlling air under pressure into a compressor main stream to divert flow between combustion and dilution streams.

According to the invention, a combustion system in which fuel may be burned continuously in a stream of air includes a combustion chamber, means associated p CC with the combustion chamber for dividing air flowing thereto into at least two streams and means operable to vary the distribution of flow between the streams wherein suction is applied to a surface forming a part of the combustion chamber in such manner as to vary the direction of air flowing over the surface.

Preferably the suction is applied through openings in said surface to act on the boundary layer of the air flowing over the surface.

Alternative embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings of which:

FIG. 1 is an axial section through a combustion chamber, and

FIG. 2 is a similar view of another combustion chamher.

The combustion system illustrated in FIG. 1 follows conventional practice, comprising a combustion chamber 1 containing a flame tube 2, which encloses the actual combustion space, and a fuel injector 3. The combustion chamber is generally cylindrical and tapers at both ends to form respectively an inlet duct 4 from a compressor (not shown) and an outlet 5 intended to be connected to a turbine inlet. The flame tube, also generally cylindrical, is mounted co-axially within the combustion chamber with one end tapering inwardly to meet the wall of the combustion chamber at the outlet 5 and the other end facing upstream towards the inlet duct 4. An annular space 6 which is closed at its downstream end and open to flow from the inlet duct at its upstream end is formed between the combustion chamber and the flame tube.

The fuel injector 3 is located on the axis of the combustion chamber adjacent to the inlet end of the flame tube so as to direct a conical spray of fuel into the flame tube as shown by the dotted lines, the fuel being supplied to the injector by a pipe 7. The fuel injector is carried by support struts 8 extending inwardly from the wall of the combustion chamber across the flow path from the inlet duct 4. The support struts also carry an annular flow divider 9 which surrounds the fuel injector and whereby a part of the incoming flow is directed round the outside of the divider towards the annular space 6, the remainder passing into the flame tube by way of an inlet passage 10 between the flow divider and the body of the fuel injector as primary combustion air. Air from the annular space 6 may pass to the interior of the flame tube by way of a row of small diameter holes 11 spaced circumferentially around the flame tube about one-third of the way along its length and by a row of larger diameter holes 12 similarly spaced about two-thirds along to constitute secondary combustion and dilution air respectively.

The flow divider 9 comprises a ring of approximately D-section, the straight side forming the inner periphery and the rounded side being slightly flattened in the upstream direction. The downstream face is spaced from the flame tube by an annular gap 13. Two concentric annular slots 14, 15 pass through the downstream face of the flow divider (i.e., that which faces towards the flame tube) and are connected by internal passages 16, 17 respectively to suction tubes 18, 19.

Normal flow through the combustion chamber when in operation is shown by the solid arrows. Air from the compressor flows in through the inlet duct 4, that which forms the primary combustion air passing through the inlet passage 10 to atomise the fuel spray from the injector. The resultant mixture is ignited by conventional means (not shown) to burn in a combustion zone situated towards the upstream end of the flame tube.

Air passing over the upstream face of the flow divider is directed to the annular space 6 to flow through the holes 11 and 12 and mix with the hot gases in the flame tube to complete the combustion process and reduce their temperatures before they pass to the outlet 5.

Some air will flow round the downstream face of the flow divider to enter the flame tube through the annular gap 13 but this will not normally be a significant quantity.

However, suction applied to the passages 16, 17 in the flow divider will act through the annular slots 14, to draw off the boundary layer in this region. As a result the rate of air flow through the annular gap 13 will increase and larger quantities of air will be directed to the combustion zone as shown by the dotted arrows. This air thus by-passes the annular space 6 and the air flow through the holes 11 and 12 is correspondingly reduced to effect a change in the combustion pattern.

The variation in flow may be controlled by the degree of suction applied and by the use of only one of the annular slots at a time. The last feature may also be utilised to change the direction of flow into the flame tube through the annular gap 13 where variations in flame length are involved. (Differential suction between the slots may also be used in this connection.)

The combustion system shown in FIG. 2 is generally similar to that of the previous embodiment and the same reference numerals are used to denote corresponding components. As before, incoming air from an inlet duct 4 is directed in part to an annular space 6 surrounding a flame tube 2 and another part of the air passes through an inlet passage 10 surrounding a fuel injector 3 into the flame tube at its upstream end. Two rows of holes for secondary combustion air are spaced circumferentially around the flame tube adjacent to its upstream end and a further row of smaller holes 31 between these and the large holes 12 for dilution air admit intermediate air.

The inlet passage 10 is defined by an annular baffle 21 spaced intermediate between the fuel injector and the flame tube and curving generally outwardly at its downstream end to extend transversely partially across the flame tube near its upstream end. A further baflie 22 extends transversely between the curved end of the baffle 21 and the wall of the flame tube. The baffles 21, 22 together with the upstream end of the flame tube bound an annular channel 23 having an upstream facing opening through which air can enter from the inlet duct 4. The opposite ends of the baflle 22 overlay the adjacent end of the baffle 21 and the wall of the flame tube to form cooling passages 24, 25 respectively from which air may be directed over the surfaces of the baffle 22 and the flame tube wall from the annular channel 23. Air from the cooling passage 25 enters the flame tube immediately upstream of the secondary air entry holes and its velocity is normally such that the secondary air is diverted in a downstream direction as shown by the arrows B near the top of the figure. The secondary air combines with combustion gases in the flame tube and with intermediate and dilution air flowing from the annular space 6 through the holes 31 and 12 to form an extended recirculation pattern as indicated on the upper half of the figure.

A circular pipe 26 is mounted within the flame tube in close proximity to the outlet from the passage 25. A series of holes 27 extend circumferentially through the surface of the pipe on its downstream side and the interior of the pipe is connected to a suction tube 28. The effect of applying suction will be to draw off some of the cooling air entering the flame tube through the passage 25 causing it to flow inwardly towards the centre of the flame tube. Thus it will not influence the secondary air so strongly and this too will tend to flow towards the centre of the flame tube as indicated by the arrows C towards the bottom of the figure with consequent reduction in the recirculation pattern.

In alternative constructions, suction can be applied through holes, meshes, porous media or other openings which permit passage of air through surfaces forming airflow boundaries or which act to divide an airflow, for example, the surfaces of flow guide vanes at a combustion chamber inlet.

Air pressure within a combustion system is usually higher than exists at other parts of a gas turbine engine. Suction may thus be readily achieved by providing connections from those locations where it is to be applied to another part of an engine or to the atmosphere. Valves may be employed to control the magnitude or application of the suction, such valves being controlled by external means or automatically by signals from sensors responding to changes in operating conditions (e.g., pressure, temperature, density, speed, flow in the engine or fuel delivery rates).

Other than acting directly on airflow to induce changes therein, suction may be employed to move a surface to cause redistribution of flow. One such arrangement is to apply suction to one side of a surface which is pivoted at or near one end and subjected to aerodynamic loading on its other side. Some form of servo-mechanism operated or controlled by the application of suction can also be envisaged.

The invention is equally applicable to any of the forms of combustion chamber, such as annular, turbo-annular and can-type (as shown) configurations, used with gas turbine engines.

I claim:

1. A combustion system for the continuous combustion of fuel in a stream of air, comprising a combustion chamber having an air inlet, part of the combustion chamber constituting a combustion zone, means arranged to direct a proportion of inlet airflow to the combustion zone,

duct means within the combustion chamber arranged to lead a significant part of other inlet airflow downstream of the combustion zone for dilution purposes, and

a surface forming a part of the combustion chamber and selectively connected to a source of suction in such manner that application of suction will induce an airflow over the surface so directed as to increase the quantity of air passing to the combustion zone during operation of the combustion system.

2. A combustion system according to claim 1 comprising at least one opening in said surface and means connected to apply suction to said opening.

3. A combustion system according to claim 1 further comprising a flame tube within the combustion chamber, holes formed in the wall of the flame tube, and a baffle whereby an airstream is directed to deflect further air entering the flame tube through the said holes, the aforesaid surface being disposed in the airstream in such manner that suction when applied will act on the boundary layer of air flowing over the surface to vary the direction of the said airstream.

4. A combustion system according to claim 1 including a flow divider disposed in the air inlet and having at least one opening extending through the surface of the flow divider, each such opening being connected to a source of suction.

5. A combustion system according to claim 4 in which the flow divider is of annular configuration.

6. A combustion system according to claim 5 further comprising a flame tube and a fuel injector arranged to direct a spray of fuel into the flame tube, the flow divider being disposed about the fuel injector.

7. A combustion system according to claim 5 having openings extending circumferentially around the flow divider.

8. A combustion system according to claim 5 having at least two concentric annular slots extending through the surface of the flow divider.

9. A combustion sytem according to claim 8 in which each slot is separately connected to a source of suction.

10. A combustion system according to claim 1 further comprising a flame tube within the combustion chamber, a fuel injector arranged to direct a spray of fuel into the flame tube, and an annular flow divider situated upstream of the flame tube and surrounding the fuel injector, wherein the flow divider includes at least two concentric annular slots extending through its surface and each slot is separately connected to a source of suction, the slots being arranged so that the application of suction will draw off the boundary layer of air flowing over the flow divider surface to vary the relative distribution of air flowing into and around the flame tube.

11. A combustion system according to claim 3 in which the baflle and the wall of the flame tube together define a passage whereby air may be directed over the flame tube wall and further comprising a perforated surface disposed adjacent to the outlet of the passage and connected to a source of suction.

References Cited UNITED STATES PATENTS 2,807,933 10/1957 Martin 6039.39 XR 2,960,823 11/1960 Fox 60-3929 XR CARLTON R. CROYLE, Primary Examiner