GB1575641A - Combustion apparatus - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO COMBUSTION APPARATUS (71) I, SECRETARY OF STATE FOR DEFENCE, London, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to combustion apparatus for the combustion of fuel in an airstream and particularly, though not exclusively, relates to combustion apparatus for use in aircraft gas turbine engines.

Smoke in the efflux of a gas turbine engine is a disadvantage which is generally overcome in prior art gas turbines by accepting some penalty in engine performance. It is known that carbon is formed during the combustion of rich fuel mixtures and that by increasing the proportion of primary air flowing into the combustion chamber smoke emissions may be reduced. However, the engine performance will be adversely affected by, for example, a reduction in combustion stability limits.

The present invention is directed towards improvements in fuel-air mixing in the primary zone of a combustion chamber in order to reduce or eliminate smoke emission.

According to the present invention, combustion apparatus for the combustion of fuel in an airstream comprises a combustion chamber, rows of air inlets at the upstream end of the chamber for admitting primary combustion air into the chamber, the rows being circumferentially spaced about the chamber axis and the areas of the inlets in each row progressively increasing in a downstream direction, and a fuel injector arranged to direct streams of fuel along the spaces between adjacent rows of inlets whereby the fuel is entrained by air from the inlets to form a fuel-air mixture therewith.

The fuel stream from the injector may include fuel droplets and/or fuel vapour.

The combustion chamber may be of can or of annular configuration and the rows of air inlets may extend radially outwards. The rows may be straight or, where swirl is imparted to the streams, the rows may be curved and the fuel streams constrained to follow the curvature of the rows.

In a preferred embodiment of the invention the air inlets are circular.

Embodiments of the invention will now be described, by way of example only, with reference to the schematic drawings accompanying the Provisional Specification of which: Figure 1 is a longitudinal section of combustion apparatus according to the invention.

Figure 2 is a cross-sectional view of the apparatus of Figure 1 taken on the line A-A in Figure 1.

Figure 3 is a longitudinal section of a further embodiment of the invention.

Figure 4 is a cross-sectional view of the embodiment of Figure 3 taken on the line B-B in Figure 3.

Figure 5 shows a sectional, scrap view of another embodiment of the invention.

Referring to the drawings, the combustion apparatus shown in Figure 1 includes a combustion chamber 8, which has a can configuration, comprising a generally cylindrical portion 5 which terminates downstream in a convergent nozzle 7, and an upstream portion comprising a conical dome 4. The cylindrical portion 5 has a pair of spaced, circumferentially extending slots 6 therein for admitting cooling air to the chamber.

Eight circumferentially spaced rows of three circular primary air inlets 3 are formed in the conical wall of the dome 4 as may be seen more clearly in Figure 2. The diameters of the inlets 3 progressively increase in the downstream direction.

The apparatus further includes a fuel injector 2 connected to a fuel tank (not shown) via a fuel supply pipe 1.

The injector 2 has eight circumferentially spaced nozzles which are arranged to direct streams of fuel droplets (as indicated by the dotted lines in the drawings) along the spaces between adjacent rows of inlets 3.

In operation, each stream of fuel from the injector is entrained by jets of primary air issuing from the inlets 3 on each side of the stream to form a fuel-air mixture for combustion.

The embodiment shown in Figure 3 includes a combustion chamber 8 of annular configuration having a portion 5 having concentric cylindrical walls which terminate downstream in annular nozzle 7, and an upstream portion 4 which is divergent in the downstream direction. The portion 5 has a pair of spaced circumferentially extending secondary air slots 6 in the wall thereof. The portion 4, which houses an annular fuel injector 11, has a series of circumferentially spaced rows containing three circular, priprimary air inlets 3 as may be seen more clearly in Figure 4. The diameters of the inlets progressively increase in the downstream direction.The fuel injector 11 has a series of inner and outer fuel nozzles which are arranged to direct streams of fuel droplets as indicated by the dotted lines in the drawing) along the spaces between adjacent rows of inlets 3, towards, and away from, the chamber axis, respectively.

Figure 5 shows part of a combustion apparatus which is generally similar to that shown in Figure 3 but which has a combustion chamber having a rounded end portion 4 and an annular, T-section fuel distributor 26.

The distributor comprises a deflector plate 25 which serves to deflect air entering the chamber via a series of slots 19 over the surface of the end portion 4 adjacent to the distributor, and a stem 20 which has a series of bores 22 which serve to supply fuel to a corresponding series of fuel nozzles 23, 24 each arranged to direct a stream of fuel along the spaces defined between the rows of inlets 3.

In operation, air enters the slots 19 and is deflected by the deflector plate 25 of the distributor outwardly from the axis Y-Y of the chamber over the surface of the rounded portion 4. Fuel from the nozzles 23, 24 is directed into the deflected airstream and between adjacent rows of inlets 3 where the fuel is entrained by the jets of air from the inlets 3 to form a fuel-air mixture for combustion.

Various modifications can with advantage be incorporated in the constructions already described. For instance an additional circumferentially extending secondary air slot (as 6) might be located at or near the change of section where end walls (as 4) join combustion chambers proper, for extra cooling or suppression of undesirable recirculation patterns.

In another modification, the rows of primary air inlets are extended along the sides of a combustion chamber for maintaining sectorisation of fuel stream flow.

Again, a deflector generally as in Figure 5 can be arranged to extend radially and axially along the direction of fuel discharge in the embodiment of Figures 3 and 4.

By using thicker combustion chamber walls, the sides of primary air inlets can be made convergent in the direction of flow therethrough and large airflow approach velocities can be utilised to vary the discharge angle of air passing through the inlets from the more usual right angle direction, to give better control of the mixing process and also to assist combustion by controlling recircu lation and mixing rates in the critical region of airjfuel mixing close to the fuel injection points.

WHAT I CLAIM IS: 1. Combustion apparatus for the com bustion of fuel in an airstream comprising a combustion chamber, rows of air inlets at the upstream end of the chamber for admitting primary combustion air into the chamber, the rows being circumferentially spaced about the chamber axis and the areas of the inlets in each row progressively increasing in a downstream direction, and a fuel injector arranged to direct streams of fuel along the spaces between adjacent rows of inlets whereby the fuel will be entrained by air from the inlets so as to form a fuel-air mixture therewith.

2. Combustion apparatus according to Claim 1 in which the combustion chamber and fuel injector are of annular form.

3. Combustion apparatus according to Claim 2 in which the fuel injector comprises nozzles disposed to direct streams of fuel towards the chamber axis and nozzles disposed to discharge streams of fuel away from the chamber axis.

4. Combustion apparatus according to Claim 2 or Claim 3 in which the fuel injector comprises a deflector arranged to deflect air from a further air inlet or inlets, and nozzles disposed to discharge streams of fuel into the deflected airstream.

5. Combustion apparatus substantially as herein described with reference to Figures 1 and 2 of the drawings accompanying the Provisional Specification.

6. Combustion apparatus substantially as herein described with reference to Figures 3 and 4 of the drawings accompanying the Provisional Specification.

7. Combustion apparatus substantially as herein described with reference to Figure 5 of the drawings accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. issuing from the inlets 3 on each side of the stream to form a fuel-air mixture for combustion. The embodiment shown in Figure 3 includes a combustion chamber 8 of annular configuration having a portion 5 having concentric cylindrical walls which terminate downstream in annular nozzle 7, and an upstream portion 4 which is divergent in the downstream direction. The portion 5 has a pair of spaced circumferentially extending secondary air slots 6 in the wall thereof. The portion 4, which houses an annular fuel injector 11, has a series of circumferentially spaced rows containing three circular, priprimary air inlets 3 as may be seen more clearly in Figure 4. The diameters of the inlets progressively increase in the downstream direction.The fuel injector 11 has a series of inner and outer fuel nozzles which are arranged to direct streams of fuel droplets as indicated by the dotted lines in the drawing) along the spaces between adjacent rows of inlets 3, towards, and away from, the chamber axis, respectively. Figure 5 shows part of a combustion apparatus which is generally similar to that shown in Figure 3 but which has a combustion chamber having a rounded end portion 4 and an annular, T-section fuel distributor 26. The distributor comprises a deflector plate 25 which serves to deflect air entering the chamber via a series of slots 19 over the surface of the end portion 4 adjacent to the distributor, and a stem 20 which has a series of bores 22 which serve to supply fuel to a corresponding series of fuel nozzles 23, 24 each arranged to direct a stream of fuel along the spaces defined between the rows of inlets 3. In operation, air enters the slots 19 and is deflected by the deflector plate 25 of the distributor outwardly from the axis Y-Y of the chamber over the surface of the rounded portion 4. Fuel from the nozzles 23, 24 is directed into the deflected airstream and between adjacent rows of inlets 3 where the fuel is entrained by the jets of air from the inlets 3 to form a fuel-air mixture for combustion. Various modifications can with advantage be incorporated in the constructions already described. For instance an additional circumferentially extending secondary air slot (as 6) might be located at or near the change of section where end walls (as 4) join combustion chambers proper, for extra cooling or suppression of undesirable recirculation patterns. In another modification, the rows of primary air inlets are extended along the sides of a combustion chamber for maintaining sectorisation of fuel stream flow. Again, a deflector generally as in Figure 5 can be arranged to extend radially and axially along the direction of fuel discharge in the embodiment of Figures 3 and 4. By using thicker combustion chamber walls, the sides of primary air inlets can be made convergent in the direction of flow therethrough and large airflow approach velocities can be utilised to vary the discharge angle of air passing through the inlets from the more usual right angle direction, to give better control of the mixing process and also to assist combustion by controlling recircu lation and mixing rates in the critical region of airjfuel mixing close to the fuel injection points. WHAT I CLAIM IS:

1. Combustion apparatus for the com bustion of fuel in an airstream comprising a combustion chamber, rows of air inlets at the upstream end of the chamber for admitting primary combustion air into the chamber, the rows being circumferentially spaced about the chamber axis and the areas of the inlets in each row progressively increasing in a downstream direction, and a fuel injector arranged to direct streams of fuel along the spaces between adjacent rows of inlets whereby the fuel will be entrained by air from the inlets so as to form a fuel-air mixture therewith.

2. Combustion apparatus according to Claim 1 in which the combustion chamber and fuel injector are of annular form.

3. Combustion apparatus according to Claim 2 in which the fuel injector comprises nozzles disposed to direct streams of fuel towards the chamber axis and nozzles disposed to discharge streams of fuel away from the chamber axis.

4. Combustion apparatus according to Claim 2 or Claim 3 in which the fuel injector comprises a deflector arranged to deflect air from a further air inlet or inlets, and nozzles disposed to discharge streams of fuel into the deflected airstream.

5. Combustion apparatus substantially as herein described with reference to Figures 1 and 2 of the drawings accompanying the Provisional Specification.

6. Combustion apparatus substantially as herein described with reference to Figures 3 and 4 of the drawings accompanying the Provisional Specification.

7. Combustion apparatus substantially as herein described with reference to Figure 5 of the drawings accompanying the Provisional Specification.