Title of Invention	A COMBUSTION APPARATUS
Abstract	The invention relates to a combustion apparatus comprising a first swirler (1) for mixing a fuel with an oxidant; a combustion chamber (3) in which combustion of the fuel/oxidant mix takes place; a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and means (5) for supplying a gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre-chamber (9), the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47), the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3), the. first swirler (1) comprising a plurality of slots (15) for guiding the gas, the slots (15) being arranged in a circle and extending generally radially inwardly, the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas, the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25).

Title of Invention

A COMBUSTION APPARATUS

Abstract

The invention relates to a combustion apparatus comprising a first swirler (1) for mixing a fuel with an oxidant; a combustion chamber (3) in which combustion of the fuel/oxidant mix takes place; a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and means (5) for supplying a gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre-chamber (9), the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47), the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3), the. first swirler (1) comprising a plurality of slots (15) for guiding the gas, the slots (15) being arranged in a circle and extending generally radially inwardly, the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas, the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25).

Full Text	FIELD OF THE INVENTION The present invention relates to a combustion apparatus. More particularly the present invention relates to a combustion apparatus comprising: a device for mixing a fuel with an oxidant; a combustion chamber in which combustion of the fuel/oxidant mix takes place; a pre-chamber located between the device and the combustion chamber; and means for supplying a gas to the pre-chamber so as to form a film of gas on the interior surface of the pre-chamber so as to prevent a combustion flame from the combustion chamber attaching itself to this interior surface damaging the pre- chamber. BACKGROUND OF THE INVENTION It is known to achieve the film of gas on the interior surface of the pre-chamber by forming holes in the walls of the pre-chamber, and supplying the gas to the pre-chamber via the holes. This has the disadvantage that where the gas. first reaches the interior surface of the pre-chamber it is in the form of a number of discrete gas flows, one gas flow from each hole. Consequently, protection of the interior surface against flame attachment is not present in respect of areas of the interior surface between the discrete gas flows. SUMMARY OF THE INVENTION According to the present invention there is provided a combustion apparatus comprising: a device for mixing a fuel with an oxidant; a combustion chamber in which combustion of the fuel/oxidant mix takes place; a pre-chamber located between the device and the combustion chamber; and means for supplying a gas to the pre-chamber so as to form a film of gas on the interior surface of the pre-chamber so as to prevent a combustion flame from the combustion chamber attaching itself to this interior surface damaging the pre- chamber, the supply of gas to the pre-chamber being such that where the gas first reaches the interior surface of the pre-chamber it forms a substantially continuous film of gas over this interior surface. In an apparatus according to the preceding paragraph, it is preferable that the means for supplying comprises a swirler for creating a swirling flow of the gas which travels over the interior surface of the pre-chamber to the combustion chamber. In an apparatus according to the preceding paragraph, it is preferable that the swirler comprises a plurality of slots for guiding the gas, the slots being arranged in a circle and extending generally radially inwardly. In an apparatus according to the preceding paragraph, it is preferable that the swirler comprises an annular base plate and a plurality of wedge pieces arranged circumferentially spaced around the annular base plate so as to form between adjacent wedge pieces the slots for guiding the gas, the wedge pieces being set back from the radially inner edge of the annular base plate thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge. It is preferable that an apparatus according to the preceding paragraph further comprises an annular closing plate secured to the swirler such that one side of the annular closing plate forms a wall of the slots, the Wedge pieces being set back from the radially inner edge of the annular closing plate thereby to define an annular ledge on the annular closing plate immediately radially outward of the radially inner edge of the annular closing plate. In an apparatus according to either of the preceding two paragraphs, it is preferable that the swirler is located between the device and the pre-chamber, and the swirler meets the pre-chamber by way of a smooth shoulder formed between the annular ledge on the annular base plate of the swirler and the interior surface of the pre-chamber. In an apparatus according to any one of the preceding three paragraphs but three, it is preferable that the means for supplying is located between the device and the pre-chamber. In an apparatus according to any one of the preceding seven paragraphs, the device may comprise a swirler for creating a swirling mix of the fuel and oxidant which travels along the pre-chamber to the combustion chamber. In an apparatus according to any one of the preceding eight paragraphs, the oxidant may be air and the gas may be air. The present invention also extends to a gas turbine engine including an apparatus according to any one of the preceding nine paragraphs, wherein compressed gas from the compressor of the engine is shared between the device and the means for supplying, the majority of the gas being supplied to device. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is an exploded perspective view of a combustion apparatus according to the present invention; Fig 2 is an exploded perspective view of the combustion apparatus of Fig 1 taken from a different perspective to that of Fig 1, and with most of a combustion chamber of the apparatus omitted; Fig 3 is an exploded side view of the apparatus of Fig 1 with the combustion chamber omitted; Fig 4 is a view on the line IV-IV in Fig 3; Fig 5 is a view on the line V-V in Fig 3; Fig 6 is a cross section on the line VI-VI in Fig 3; Fig 7 is a side view of the apparatus of Fig 1 when assembled with the combustion chamber omitted; Fig 8 is a cross section on the line VIII-VIII in Fig 7; Fig 9 is a cross section on the line IX-IX in Fig 7; and Fig 10 is a schematic cross section along the length of the apparatus of Fig 1. DETAIL DESCRIPTION OF THE INVENTION Referring to the drawings, the apparatus comprises a first swirler 1 for creating a swirling mix of a fuel and air, a combustion chamber 3 in which combustion of the fuel/air mix takes place, a second swirler 5 for creating a swirling flow of air, an annular closing plate 7 that separates swirlers 1 and 5, and a pre-chamber 9 located between second swirler 5 and combustion chamber 3. First swirler 1 comprises an annular base plate 11, and a plurality of wedge pieces 13 arranged circumferentially spaced around annular base plate 11 so as to form, between adjacent wedge pieces 13, slots 15. Plate 11 includes at the radially outer end of each slot 15 a port 17 by means of which fuel is supplied to first swirler 1. Each wedge piece 13 includes at the radially outer end of one side 19 thereof a hole 21 by means of which fuel is also supplied to first swirler 1. A plurality of fixing holes 23 extend through wedge pieces 13 and base plate 11. The radially inner thin ends 25 of wedge pieces 13 are set back from the radially inner edge 27 of annular base plate 11 thereby to define an annular ledge 29 immediately radially outward of edge 27. Second swirler 5 is similar in form to first swirler 1 and comprises an annular base plate 31, and a plurality of wedge pieces 33 arranged circumferentially spaced around annular base plate 31 so as to form, between adjacent wedge pieces 33, slots 35. The height of wedge pieces 33 above base plate 31 is much reduced as compared to the height of wedge pieces 13 above base plate 11 in first swirler 1. A plurality of fixing holes 37 extend through wedge pieces 33 and base plate 31. The radially inner thin ends 39 of wedge pieces 33 are set back from the radially inner edge 41 of annular base plate 31 thereby to define an annular ledge 43 immediately radially outward of edge 41. Pre-chamber 9 is cylindrical in form and has an interior surface 47. Pre-chamber 9 is formed integrally with second swirler 5. In this regard, at the point where pre-chamber 9 meets second swirler 5, a smooth 90° shoulder 49 is formed between interior surface 47 of pre-chamber 9 and annular ledge 43 of second swirler 5. Annular closing plate 7 includes a plurality of fixing holes 45. First swirler 1, annular closing plate 7, and second swirler 5 (together with integrally formed pre-chamber 9) are secured together by means of nut and bolt fixings utilising fixing holes 23 in swirler 1, 45 in plate 7, and 37 in swirler 5. Thus, one side of plate 7 forms a wall of each of slots 15 of first swirler 1, and the other side of plate 7 forms a wall of each of slots 35 of second swirler 5. The relationship of wedge pieces 13 of first swirler 1 to annular closing plate 7 can be seen in Fig 8. The radially inner thin ends 25 of wedge pieces 13 extend precisely as far as the radially inner edge 51 of annular closing plate 7. The relationship of wedge pieces j3 of second swirler 5 to annular closing plate 7 can be seen in Fig 9. The radially inner thin ends 39 of wedge pieces 33 are set back from the radially inner edge 51 of annular closing plate 7 thereby to define an annular ledge 53 immediately radially outward of edge 51. Operation of the combustion apparatus will now be described. Air is supplied to the radially outer ends of slots 15 of first swirler 1 and travels generally radially inwardly along slots 15. Fuel is supplied to ports 17 and holes 21 of first swirler 1 so as to enter slots 15 and mix with the air travelling along slots 15. Thus, first swirler 1 creates a swirling mix of fuel and air in an annular region immediately radially inward of the radially inner ends of slots 15, see arrows 55 in Fig 8. This swirling mix travels axially along the apparatus to combustion chamber 3, passing through annular closing plate 7, second swirler 5, and pre-chamber 9, see arrows 57 in Fig 10. Ignition of the fuel/air mix is achieved by means of an ignition device (not shown) located in the circular opening of annular base plate 11 of first swirler 1. In this regard, the combustion apparatus includes a further part (not shown) disposed to the left of the apparatus as shown in Fig 1, which part includes a face that occupies the circular opening of annular base plate 11. The ignition device is disposed within this face. Following ignition by the ignition device, the combustion is self-sustaining. Air is also supplied to the radially outer ends of slots 35 of second swirler 5 and travels generally radially inwardly along slots 35. Thus, second swirler 5 creates a swirling flow of air in an annular region immediately radially inward of the radially inner ends of slots 35, see arrows 59 in Fig 4. This swirling flow swirls between annular ledge 53 of annular closing plate 7 and annular ledge 43 of second swirler 5, passes over 90° shoulder 49 between annular ledge 43 and interior surface 47 of pre-chamber 9, and travels axially along pre-chamber 9 to combustion chamber 3, see arrows 61 in Fig 10. The purpose of the air flow provided by second swirler 5 is to provide a film of air on interior surface 47 of pre- chamber 9 thereby to prevent a combustion flame from combustion chamber 3 attaching itself to interior surface 47 damaging pre-chamber 9. The supply of air by second swirler 5 is such that where the air first reaches interior surface 47, i.e. following 90° shoulder 49, it forms a continuous film of air over interior surface 47. This continuous nature is due to (i) the presence of annular ledge 43, created by setting back Wedge pieces 33 from edge 41 of second swirler 5, (ii) the presence of annular ledge 53, created by setting back wedge pieces 33 from edge 51 of annular closing plate 7, and (ii)) the presence of 90° shoulder 49 between second swirler 5 and pre-chamber 9. The design intent is that the velocity of the air flow from second swirler 5, see arrows 61 in Fig 10, is as close as possible to the velocity of the fuel/air mix from first swirler 1, see arrows 57 in Fig 10. In this way there is minimum disturbance of air flow 61 by mix flow 57, minimising corruption of protective air film 61. In the above described apparatus, a protective film of air is provided on the interior surface of pre-chamber 9. It is to be realised that this protective film need not be of air but could be of another gas, e.g. carbon dioxide. Similarly, the protective film could be a mix of a gaseous fuel and air, provided the particular mix used (concentration of the fuel in the air) does not ignite in the conditions present in pre- chamber 9 in the region of the interior surface of pre- chamber 9. Thus, a lean mix could be used wherein the concentration of the fuel is below that at which ignition can occur, or a rich mix could be used wherein the concentration of fuei is above that at which ignition can occur. Indeed, in the case of the rich mix, the concentration of the fuel could be 100 percent, i.e. no air present. In the above described apparatus, a swirler is used to provide a mix of fuel and air for combustion. It is to be realised that the fuel/air mix could be provided by an alternative device able to provide a sufficiently homogeneous mix of fuel and air. In the above described apparatus, a swirler is used to supply air for the protective film on the interior surface of pre- chamber 9. It is to be realised, that an alternative means could be used for this purpose, provided the supply of air is such that where the air first reaches the interior surface it forms a substantially continuous film of air over this surface. In the apparatus described above, second swirler 5 is located immediately prior to pre-chamber 9. It is to be realised that swirler 5 could be located partway along the length of pre- chamber 9, such that the protective film of air is provided only in respect of the remaining portion of pre-chamber 9 between swirler 5 and combustion chamber 3. Further, the apparatus could include two second swirlers 5, one located immediately prior to pre-chamber 9, the other located partway along the length of pre-chamber 9. The swirler 5 located partway along the length of pre-chamber 9 would then provide protective air to supplement that provided by the swirler 5 located immediately prior to pre-chamber 9. This supplementary air would assist in the protection of pre- chamber 9 downstream of the swirler 5 located partway along the length of the pre-chamber. The present invention finds particular application in gas turbine engines. In the case of the apparatus described above, compressed air from the compressor of the engine would be shared between first swirler 1 and second swirler 5, the majority of the air being supplied to first swirler 1. The present invention is particularly useful in the combustion of fuels of high flame speed. When using such fuels there is a greater tendency for a combustion flame from the combustion chamber to flashback to the pre-chamber and attach itself to the interior surface of the pre-chamber. WE CLAIM i. A combustion apparatus comprising: a first swirler (1) for mixing a fuel with an oxidant; a combustion chamber (3) in which combustion of the fuel/oxidant mix takes place; a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and means (5) for supplying a'gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre- chamber (9), the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47), the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3), the first swirler (1) comprising a plurality of slots (15) for guiding the gas, the slots (15) being arranged in a circle and extending generally radially inwardly, the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas, the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25). 2. An apparatus as claimed in claim 1, comprising an annular closing plate (7) secured to the second swirler (5) such that one side of the annular closing plate (7) forms a wall of the slots (15), a plurality wedge pieces (33) being set back from a radially inner edge (51) of the annular closing plate (7) thereby to define an annular ledge (53) on the annular closing plate (7) immediately radially outward of the radially inner edge (51) of the annular closing plate (7). 3. An apparatus as claimed in claim 1 or claim 2, wherein the second swirler (5) is located between the first swirler (1) and the pre-chamber (9), and the second swirler (5) meets the pre-chamber (9) by way of a smooth shoulder (49) formed between the annular ledge (43) on the annular base plate (11) of the second swirler (5) and the interior surface (47) of the pre-chamber (9). 4. An apparatus as claimed in claim 1, wherein the second swirler (5) is located between the device (1) and the pre-chamber (9). 5. An apparatus as claimed in any one of the preceding claims wherein the first swirler (1) for creating a swirling mix of the fuel and oxidant which travels along the pre-chamber (9) to the combustion chamber (3). 6. An apparatus as claimed in any one of the preceding claims wherein the oxidant is air and the gas is air. 7.^^85 turbine engine comprising an apparatus as claimed in any one of / the preceding claims, wherein compressed gas from the compressor of the engine is shared between the first swirler (1) and the second swirler (5), the majority of the gas being supplied to the first swirler (1). ABSTRACT TITLE : A COMBUSTION APPARATUS" The invention relates to a combustion apparatus comprising a first swirler (1) for mixing a fuel with an oxidant; a combustion chamber (3) in which combustion of the fuel/oxidant mix takes place; a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and means (5) for supplying a gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre-chamber (9), the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47), the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3), the. first swirler (1) comprising a plurality of slots (15) for guiding the gas, the slots (15) being arranged in a circle and extending generally radially inwardly, the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas, the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25).

Full Text

FIELD OF THE INVENTION
The present invention relates to a combustion apparatus.
More particularly the present invention relates to a combustion apparatus comprising: a device for mixing a fuel with an oxidant; a combustion chamber in which combustion of the fuel/oxidant mix takes place; a pre-chamber located between the device and the combustion chamber; and means for supplying a gas to the pre-chamber so as to form a film of gas on the interior surface of the pre-chamber so as to prevent a combustion flame from the combustion chamber attaching itself to this interior surface damaging the pre- chamber.
BACKGROUND OF THE INVENTION
It is known to achieve the film of gas on the interior surface of the pre-chamber by forming holes in the walls of the pre-chamber, and supplying the gas to the pre-chamber via the holes. This has the disadvantage that where the gas. first reaches the interior surface of the pre-chamber it is in the form of a number of discrete gas flows, one gas flow from each hole. Consequently, protection of the interior surface against flame attachment is not present in respect of areas of the interior surface between the discrete gas flows.
SUMMARY OF THE INVENTION
According to the present invention there is provided a combustion apparatus comprising: a device for mixing a fuel with an oxidant; a combustion chamber in which combustion of the fuel/oxidant mix takes place; a pre-chamber located

between the device and the combustion chamber; and means for supplying a gas to the pre-chamber so as to form a film of gas on the interior surface of the pre-chamber so as to prevent a combustion flame from the combustion chamber attaching itself to this interior surface damaging the pre- chamber, the supply of gas to the pre-chamber being such that where the gas first reaches the interior surface of the pre-chamber it forms a substantially continuous film of gas over this interior surface.
In an apparatus according to the preceding paragraph, it is preferable that the means for supplying comprises a swirler for creating a swirling flow of the gas which travels over the interior surface of the pre-chamber to the combustion chamber.
In an apparatus according to the preceding paragraph, it is preferable that the swirler comprises a plurality of slots for guiding the gas, the slots being arranged in a circle and extending generally radially inwardly.
In an apparatus according to the preceding paragraph, it is preferable that the swirler comprises an annular base plate and a plurality of wedge pieces arranged circumferentially spaced around the annular base plate so as to form between adjacent wedge pieces the slots for guiding the gas, the wedge pieces being set back from the radially inner edge of the annular base plate thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge.
It is preferable that an apparatus according to the preceding paragraph further

comprises an annular closing plate secured to the swirler such that one side of the annular closing plate forms a wall of the slots, the Wedge pieces being set back from the radially inner edge of the annular closing plate thereby to define an annular ledge on the annular closing plate immediately radially outward of the radially inner edge of the annular closing plate.
In an apparatus according to either of the preceding two paragraphs, it is preferable that the swirler is located between the device and the pre-chamber, and the swirler meets the pre-chamber by way of a smooth shoulder formed between the annular ledge on the annular base plate of the swirler and the interior surface of the pre-chamber.
In an apparatus according to any one of the preceding three paragraphs but three, it is preferable that the means for supplying is located between the device and the pre-chamber.
In an apparatus according to any one of the preceding seven paragraphs, the device may comprise a swirler for creating a swirling mix of the fuel and oxidant which travels along the pre-chamber to the combustion chamber.
In an apparatus according to any one of the preceding eight paragraphs, the oxidant may be air and the gas may be air.
The present invention also extends to a gas turbine engine including an apparatus according to any one of the preceding nine paragraphs, wherein

compressed gas from the compressor of the engine is shared between the device and the means for supplying, the majority of the gas being supplied to device.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Fig 1 is an exploded perspective view of a combustion apparatus according to the present invention;
Fig 2 is an exploded perspective view of the combustion apparatus of Fig 1 taken from a different perspective to that of Fig 1, and with most of a combustion chamber of the apparatus omitted;
Fig 3 is an exploded side view of the apparatus of Fig 1 with the combustion chamber omitted;
Fig 4 is a view on the line IV-IV in Fig 3;
Fig 5 is a view on the line V-V in Fig 3;
Fig 6 is a cross section on the line VI-VI in Fig 3; Fig 7 is a side view of the apparatus of Fig 1 when assembled with the combustion chamber omitted;
Fig 8 is a cross section on the line VIII-VIII in Fig 7;

Fig 9 is a cross section on the line IX-IX in Fig 7; and
Fig 10 is a schematic cross section along the length of the apparatus of Fig 1.
DETAIL DESCRIPTION OF THE INVENTION
Referring to the drawings, the apparatus comprises a first swirler 1 for creating a swirling mix of a fuel and air, a combustion chamber 3 in which combustion of the fuel/air mix takes place, a second swirler 5 for creating a swirling flow of air, an annular closing plate 7 that separates swirlers 1 and 5, and a pre-chamber 9 located between second swirler 5 and combustion chamber 3.
First swirler 1 comprises an annular base plate 11, and a plurality of wedge pieces 13 arranged circumferentially spaced around annular base plate 11 so as to form, between adjacent wedge pieces 13, slots 15. Plate 11 includes at the radially outer end of each slot 15 a port 17 by means of which fuel is supplied to first swirler 1. Each wedge piece 13 includes at the radially outer end of one side 19 thereof a hole 21 by means of which fuel is also supplied to first swirler 1. A plurality of fixing holes 23 extend through wedge pieces 13 and base plate 11. The radially inner thin ends 25 of wedge pieces 13 are set back from the radially inner edge 27 of annular base plate 11 thereby to define an annular ledge 29 immediately radially outward of edge 27.
Second swirler 5 is similar in form to first swirler 1 and comprises an annular base plate 31, and a plurality of wedge pieces 33 arranged circumferentially spaced around annular base plate 31 so as to form, between adjacent wedge

pieces 33, slots 35. The height of wedge pieces 33 above base plate 31 is much reduced as compared to the height of wedge pieces 13 above base plate 11 in first swirler 1. A plurality of fixing holes 37 extend through wedge pieces 33 and base plate 31. The radially inner thin ends 39 of wedge pieces 33 are set back from the radially inner edge 41 of annular base plate 31 thereby to define an annular ledge 43 immediately radially outward of edge 41.
Pre-chamber 9 is cylindrical in form and has an interior surface 47. Pre-chamber 9 is formed integrally with second swirler 5. In this regard, at the point where pre-chamber 9 meets second swirler 5, a smooth 90° shoulder 49 is formed between interior surface 47 of pre-chamber 9 and annular ledge 43 of second swirler 5.
Annular closing plate 7 includes a plurality of fixing holes 45.
First swirler 1, annular closing plate 7, and second swirler 5 (together with integrally formed pre-chamber 9) are secured together by means of nut and bolt fixings utilising fixing holes 23 in swirler 1, 45 in plate 7, and 37 in swirler 5. Thus, one side of plate 7 forms a wall of each of slots 15 of first swirler 1, and the other side of plate 7 forms a wall of each of slots 35 of second swirler 5. The relationship of wedge pieces 13 of first swirler 1 to annular closing plate 7 can be seen in Fig 8. The radially inner thin ends 25 of wedge pieces 13 extend precisely as far as the radially inner edge 51 of annular closing plate 7. The relationship of wedge pieces j3 of second swirler 5 to annular closing plate 7 can be seen in Fig 9. The radially inner thin ends 39 of wedge pieces 33 are set back from the

radially inner edge 51 of annular closing plate 7 thereby to define an annular ledge 53 immediately radially outward of edge 51.
Operation of the combustion apparatus will now be described.
Air is supplied to the radially outer ends of slots 15 of first swirler 1 and travels generally radially inwardly along slots 15. Fuel is supplied to ports 17 and holes 21 of first swirler 1 so as to enter slots 15 and mix with the air travelling along slots 15. Thus, first swirler 1 creates a swirling mix of fuel and air in an annular region immediately radially inward of the radially inner ends of slots 15, see arrows 55 in Fig 8. This swirling mix travels axially along the apparatus to combustion chamber 3, passing through annular closing plate 7, second swirler 5, and pre-chamber 9, see arrows 57 in Fig 10.
Ignition of the fuel/air mix is achieved by means of an ignition device (not shown) located in the circular opening of annular base plate 11 of first swirler 1. In this regard, the combustion apparatus includes a further part (not shown) disposed to the left of the apparatus as shown in Fig 1, which part includes a face that occupies the circular opening of annular base plate 11. The ignition device is disposed within this face. Following ignition by the ignition device, the combustion is self-sustaining. Air is also supplied to the radially outer ends of slots 35 of second swirler 5 and travels generally radially inwardly along slots 35. Thus, second swirler 5 creates a swirling flow of air in an annular region immediately radially inward of the radially inner ends of slots 35, see arrows 59 in Fig 4. This swirling flow swirls between annular ledge 53 of annular closing plate 7 and annular ledge 43 of second swirler 5, passes over 90° shoulder 49

between annular ledge 43 and interior surface 47 of pre-chamber 9, and travels axially along pre-chamber 9 to combustion chamber 3, see arrows 61 in Fig 10.
The purpose of the air flow provided by second swirler 5 is to provide a film of air on interior surface 47 of pre- chamber 9 thereby to prevent a combustion flame from combustion chamber 3 attaching itself to interior surface 47 damaging pre-chamber 9. The supply of air by second swirler 5 is such that where the air first reaches interior surface 47, i.e. following 90° shoulder 49, it forms a continuous film of air over interior surface 47. This continuous nature is due to (i) the presence of annular ledge 43, created by setting back Wedge pieces 33 from edge 41 of second swirler 5, (ii) the presence of annular ledge 53, created by setting back wedge pieces 33 from edge 51 of annular closing plate 7, and (ii)) the presence of 90° shoulder 49 between second swirler 5 and pre-chamber 9.
The design intent is that the velocity of the air flow from second swirler 5, see arrows 61 in Fig 10, is as close as possible to the velocity of the fuel/air mix from first swirler 1, see arrows 57 in Fig 10. In this way there is minimum disturbance of air flow 61 by mix flow 57, minimising corruption of protective air film 61. In the above described apparatus, a protective film of air is provided on the interior surface of pre-chamber 9. It is to be realised that this protective film need not be of air but could be of another gas, e.g. carbon dioxide. Similarly, the protective film could be a mix of a gaseous fuel and air, provided the particular mix used (concentration of the fuel in the air) does not ignite in the conditions present in pre- chamber 9 in the region of the interior surface of pre- chamber 9. Thus, a lean mix could be used wherein the concentration of the fuel is below that at

which ignition can occur, or a rich mix could be used wherein the concentration of fuei is above that at which ignition can occur. Indeed, in the case of the rich mix, the concentration of the fuel could be 100 percent, i.e. no air present.
In the above described apparatus, a swirler is used to provide a mix of fuel and air for combustion. It is to be realised that the fuel/air mix could be provided by an alternative device able to provide a sufficiently homogeneous mix of fuel and air.
In the above described apparatus, a swirler is used to supply air for the protective film on the interior surface of pre- chamber 9. It is to be realised, that an alternative means could be used for this purpose, provided the supply of air is such that where the air first reaches the interior surface it forms a substantially continuous film of air over this surface.
In the apparatus described above, second swirler 5 is located immediately prior to pre-chamber 9. It is to be realised that swirler 5 could be located partway along the length of pre- chamber 9, such that the protective film of air is provided only in respect of the remaining portion of pre-chamber 9 between swirler 5 and combustion chamber 3. Further, the apparatus could include two second swirlers 5, one located immediately prior to pre-chamber 9, the other located partway along the length of pre-chamber 9. The swirler 5 located partway along the length of pre-chamber 9 would then provide protective air to supplement that provided by the swirler 5 located immediately prior to pre-chamber 9. This supplementary air would assist in the protection of pre-

chamber 9 downstream of the swirler 5 located partway along the length of the pre-chamber.
The present invention finds particular application in gas turbine engines. In the case of the apparatus described above, compressed air from the compressor of the engine would be shared between first swirler 1 and second swirler 5, the majority of the air being supplied to first swirler 1.
The present invention is particularly useful in the combustion of fuels of high flame speed. When using such fuels there is a greater tendency for a combustion flame from the combustion chamber to flashback to the pre-chamber and attach itself to the interior surface of the pre-chamber.

WE CLAIM
i. A combustion apparatus comprising:
a first swirler (1) for mixing a fuel with an oxidant;
a combustion chamber (3) in which combustion of the fuel/oxidant mix
takes place;
a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and
means (5) for supplying a'gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre- chamber (9),
the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47),
the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3),
the first swirler (1) comprising a plurality of slots (15) for guiding the gas,
the slots (15) being arranged in a circle and extending generally radially

inwardly,
the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas,
the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25).
2. An apparatus as claimed in claim 1, comprising an annular closing plate (7) secured to the second swirler (5) such that one side of the annular closing plate (7) forms a wall of the slots (15), a plurality wedge pieces (33) being set back from a radially inner edge (51) of the annular closing plate (7) thereby to define an annular ledge (53) on the annular closing plate (7) immediately radially outward of the radially inner edge (51) of the annular closing plate (7).
3. An apparatus as claimed in claim 1 or claim 2, wherein the second swirler (5) is located between the first swirler (1) and the pre-chamber (9), and the second swirler (5) meets the pre-chamber (9) by way of a smooth shoulder (49) formed between the annular ledge (43) on the annular base plate (11) of the second swirler (5) and the interior surface (47) of the pre-chamber (9).
4. An apparatus as claimed in claim 1, wherein the second swirler (5) is

located between the device (1) and the pre-chamber (9).
5. An apparatus as claimed in any one of the preceding claims wherein the
first swirler (1) for creating a swirling mix of the fuel and oxidant which
travels along the pre-chamber (9) to the combustion chamber (3).
6. An apparatus as claimed in any one of the preceding claims wherein the
oxidant is air and the gas is air.
7.^^85 turbine engine comprising an apparatus as claimed in any one of / the preceding claims, wherein compressed gas from the compressor of the engine is shared between the first swirler (1) and the second swirler (5), the majority of the gas being supplied to the first swirler (1).

ABSTRACT

TITLE : A COMBUSTION APPARATUS"
The invention relates to a combustion apparatus comprising a first swirler (1) for mixing a fuel with an oxidant; a combustion chamber (3) in which combustion of the fuel/oxidant mix takes place; a pre-chamber (9) located between the first swirler (1) and the combustion chamber (3); and means (5) for supplying a gas to the pre-chamber (9) so as to form a film of gas on an interior surface (47) of the pre-chamber (9) so as to prevent a combustion flame from the combustion chamber (3) attaching itself to this interior surface (47) damaging the pre-chamber (9), the supply of gas to the pre-chamber (9) being such that where the gas first reaches the interior surface (47) of the pre- chamber (9) it forms a substantially continuous film of gas over this interior surface (47), the means (5) for supplying gas is a second swirler and creating a swirling flow of the gas which travels over the interior surface (47) of the pre-chamber (9) to the combustion chamber (3), the. first swirler (1) comprising a plurality of slots (15) for guiding the gas, the slots (15) being arranged in a circle and extending generally radially inwardly, the first swirler (1) comprising an annular base plate (11) and a plurality of wedge pieces (13) arranged circumferentially spaced around the annular base plate (11) so as to form between adjacent wedge pieces (13) the slots (15) for guiding the gas, the wedge pieces (13) being set back from the radially inner edge (25) of the annular base plate (11) thereby to define an annular ledge on the annular base plate immediately radially outward of the radially inner edge (25).

A COMBUSTION APPARATUS

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