A TURBOMACHINE COMBUSTION CHAMBER WITH HELICAL AIR FLOW
Background of the invention
The present invention relates to the general field of combustion chambers for an aviation or terrestrial turbomachine.
Typically, an aviation or terrestrial turbomachine comprises an assembly made up in particular of: an annular compression section for compressing the air that passes through the turbomachine; an annular combustion section located at the outlet from the compression section and in which the air coming from the compression section is mixed with fuel in order to be burnt therein; and an annular turbine section disposed at the outlet from the combustion section and having a rotor that is driven in rotation by the gas coming from the combustion section.
The compression section is in the form of a plurality of rotor wheel stages, each carrying blades that are located in an annular channel through which the turbomachine air passes and of section that decreases from upstream to downstream. The combustion section comprises a combustion chamber in the form of an annular channel in which the compressed air is mixed with fuel in order to be burnt therein. The turbine section is made up of a plurality of rotor wheel stages, each carrying blades that are located in an annular channel through which the combustion gas passes.
The flow of air through the above assembly generally takes place as follows: the compressed air coming from the last stage of the compression section possesses natural gyratory motion with an angle of inclination of the order of 3 5° to 45° relative to the longitudinal axis of the turbomachine, which angle of inclination varies as a function of the speed of the turbomachine (speed of rotation). At its inlet into the combustion section, this compressed air has its flow straightened to becomeparallel with the longitudinal axis of the turbomachine (i.e. the angle of inclination of the air relative to the longitudinal axis of the turbomachine is brought back to 0°) by means of air flow straightener vanes. The air in the combustion chamber is then mixed with the fuel so as to provide satisfactory combustion, and the gas produced by the combustion continues to flow generally along the longitudinal axis of the turbomachine so as to reach the turbine section. In the turbine section, the combustion gas is redirected by a nozzle so as to present gyratory motion with an angle of inclination greater than 70° relative to the longitudinal axis of the turbomachine. Such an angle of inclination is essential for producing the angle of attack needed to provide the mechanical force for imparting rotary drive to the rotor wheel of the first stage of the turbine section.
Such an angular distribution for the air passing through the turbomachine presents numerous drawbacks. The air that leaves the last stage of the compression section naturally presents an angle lying in the range 34° to 45° and its flow is successively straightened out (angle returned to 0?) on entering into the combustion chamber, and is then redirected to have an angle greater than 70° at its entry into the turbine section. Those successive changes to the angle of inclination of the air flow through the turbomachine require intense aerodynamic forces to be produced by the flow-straightener vanes of the compression section and by the nozzle of the turbine section, which aerodynamic forces are particularly harmful to the overall efficiency of the turbomachine.
Object and summary of the invention
The present invention seeks to remedy the above-mentioned drawbacks by proposing a turbomachine combustion chamber that is capable of being fed with air that possesses rotary motion about the longitudinal axis of the turbomachine. 'This object is achieved by a turbomachine combustion chamber comprising:
• an inner annular wall about a longitudinal axis;
• an outer annular wall centered on the longitudinal axis and surrounding the inner wall so as to co-operate therewith to define an annular space forming a combustion area; and
• a plurality of fuel injector systems comprising pilot injectors alternating circumferentially with full-throttle injectors;
the combustion chamber being characterized in that it further comprises at least one air admission opening opening out into the upstream end of the combustion area in a direction that is substantially longitudinal;
in that the outer wall includes a plurality of pilot cavities that are regularly distributed around the longitudinal axis, each pilot cavity extending longitudinally between the two longitudinal ends of the outer wall and radially towards the outside thereof, the pilot cavities being fed with air from outside the combustion chamber in a common substantially circumferential direction; and
in that each pilot injector opens out radially into a pilot cavity, and each full-throttle injector opens out radially between said adjacent pilot cavities.
The combustion chamber of the invention can be fed with air that possesses rotary motion about the longitudinal axis of the turbomachine. The natural angle of inclination of the air at the outlet from the compression section of the turbomachine can thus be maintained through the combustion chamber. As a result, the aerodynamic force required for imparting rotary drive to the first stage of the turbine section of the turbomachine is considerably reduced. This large reduction in the aerodynamic forces gives rise to increased efficiency for the turbomachine. In addition, both the flow-straightener vanes of the compressionsection and the nozzle of the turbine section can be simplified, or even eliminated, thereby presenting a saving in weight and a reduction in manufacturing costs.
Furthermore, the presence of pilot cavities, that are carburated solely for idling speeds of the turbomachine makes it possible to stabilize the combustion flame at all operating speeds of the turbomachine.
According to an advantageous disposition, each pilot cavity is closed at its upstream end and open at its downstream end.
According to another advantageous disposition, each pilot cavity is defined circumferentially by two substantially radial partitions, one of the partitions including a plurality of air injection orifices open to the outside of the combustion chamber and leading to said pilot cavity. Preferably, the other partition of each pilot cavity presents in cross-sectibn, a section that is substantially curvilinear.
In yet another advantageous disposition, the full-throttle injectors are offset axialiy downstream relative to the pilot injectors. The flame coming from the pilot injectors requires a longer transit time in the combustion area than does the flame coming from the full-throttle injectors.
The combustion chamber need not have a wall transversely interconnecting the upstream longitudinal ends of the inner and outer wails. The absence of such a wall (referred to as the chamber end wall) makes it possible to preserve a maximum amount of the rotary motion of the air coming from the combustion section of the turbomachine.
According to yet another advantageous disposition, the fuel injector systems do not have associated air systems.
The combustion chamber may also include an inner annular fairing mounted on the inner wall extending theupstream end thereof, and an outer annular fairing mounted on the outer wall and extending the upstream end thereof.
The invention also provides a turbomachine including a combustion chamber as defined above.
Brief description of the drawings
Other characteristics and advantages of the present invention appear from the following description with reference to the accompanying drawings that show an embodiment having no limiting character. In the figures:
• Figure 1 is a fragmentary longitudinal section view of an aviation turbomachine fitted with a combustion chamber of the invention;,
• Figure 2 is a perspective view of the Figure 1 combustion chamber;
• Figure 3 is a front view of the Figure 2 combustion chamber;
• Figures 4 and 5 are section views on lines IV and V respective of Figure 3; and
• Figure 6 is a fragmentary front view of a combustion chamber in a variant embodiment of the invention.
Detailed description of embodiments
The turbomachine shown in part in Figure 1 has a longitudinal axis X-X. Along this axis, it comprises in particular: an annular compression section 100; an annular combustion section 200 disposed at the outlet from the compression section 100 in the flow direction of the air passing through the turbomachine; and an annular turbine section 300 disposed at the outlet from the combustion section 200. Air injected into the turbomachine thus passes in succession through the compression section 100, then the combustion section 200, and finally the turbine section 3.The compression section 100 is in the form of a plurality of rotor wheels 102 each carrying blades 104 (only the last stage of the compression section is shown in Figure 1). The blades 104 of these stages are disposed in an annular channel 106 through which turbomachine air passes and of section that decreases going from upstream to downstream. Thus, as the air injected into the turbomachine passes through the compression section, it becomes more and more compressed.
The combustion section 200 is also in the form of an annular channel through which the compressed air coming from the compression section 100 is mixed with fuel in order to be burnt. For this purpose, the combustion section comprises a combustion chamber 2 02 within which the air/fuel mixture is burnt (this chamber is described in greater detail below).
The combustion section 200 also has a turbomachine casing constituted by an outer annular shroud 2 04 centered on the longitudinal axis X-X of the turbomachine, and an inner annular shroud 206 that is fastened coaxially inside the outer shroud. An annular space 208 formed between these two shrouds 204, 206 receives the compressed air coming from the compression section 10 0 of the turbomachine.
The turbine section 3 00 of the turbomachine is formed by a plurality of stages of rotor wheels 3 02, each carrying blades 3 04 (only the first stage of the turbine section is shown in Figure 1). The blades 3 04 of these stages are placed in an annular channel 3 06 through which the gas coming from the combustion section 2 00 passes.
At the inlet to the first stage 3 02 of the turbine section 300, the gas coming from the combustion section needs to present an angle of inclination relative to the longitudinal axis X-X of the turbomachine that is sufficient to drive the various stages of the turbine section in rotation.of inclination in order to reduce the angle of attack needed for providing the mechanical force for imparting rotary drive to the rotor wheel 3 02 of the first stage of the turbine section.
For this purpose, the combustion chamber 2 02 of the invention has an inner annular wall 212 that is centered on the longitudinal axis X-X of the turbomachine, and an outer annular wall 2 04 that is likewise centered on the longitudinal axis X-X and that surrounds the inner wall so as to co-operate therewith to define an annular space 216 forming a combustion area.
The combustion chamber 202 of the invention also has at least one air admission opening 218 that opens out into the combustion area 216 at its upstream end and in a direction that is substantially longitudinal. The section of this air admission opening is adapted to ensure that the combustion area functions correctly.
More precisely, and as shown in Figure 1, the combustion chamber is provided with a wall (chamber end wall) transversely interconnecting the upstream longitudinal ends of the inner and outer walls, with this air admission opening 208 being formed between the upstream ends of the inner and outer walls 212 and 214 of the combustion chamber.
The combustion chamber 202 of the invention also has a plurality of fuel injector systems 220 distributed around the outer wall 214 about the longitudinal axis X-X of the turbomachine and opening out into the combustion area 216 in a substantially radial direction.
As shown in Figures 2 and 3, the fuel injector systems 220 comprise pilot injectors 220a alternating circumferentially with full-throttle injectors 220b, the full-throttle injectors preferably being offset axially downstream relative to the pilot injectors.
Conventionally, the pilot injectors 220a serve for ignition purposes and also during idling of the turbomachine, while the full-throttle injectors 220boperate during stages of takeoff, climbing, and cruising. In general, the pilot injectors are fed with fuel continuously, whereas the takeoff injectors are fed only above a certain speed.
According to a particular advantageous characteristic of the invention, the fuel injector systems 22 0 do not have associated air systems such as air swirlers serving in known manner to generate a rotary flow of air within the combustion area for the purpose of stabilizing the combustion flame.
Thus, the pilot and full-throttle injectors of the combustion chamber are of very simple design and they operate very reliably since they perform their primary function only, i.e. they inject fuel. In addition, the pilot injectors 220a are of the same type as the full-throttle injectors 220b.
Still in accordance with the invention, the outer wall 214 of the combustion chamber has a plurality of pilot cavities 222 that are regularly distributed around the longitudinal axis X-X.
As shown in Figure 2, each pilot cavity 222 extends firstly longitudinally between the two longitudinal ends (upstream and downstream) of the outer wall 214, and secondly radially towards the outside thereof. ' In other words, outer wall 214 is shaped to have a plurality of cavities 222 that project towards the outside of the wall.
More precisely, each pilot cavity 222 is defined circumferentially by two partitions 224, each projecting radially outwards relative to the outer wall 214. As shown in Figures 2 and 5, one of these partitions presents a plurality of air injection orifices 226 that enable air outside the combustion chamber to be injected into the pilot cavity in a circumferential direction.
It should be observed that the air is injected circumferentially in the same direction of rotation (clockwise in the example of Figures 2 and 3) into all ofthe pilot cavities 222 of the combustion chamber. Furthermore, the direction of rotation used for circumferential injection of air into the pilot cavities is the same as the direction of rotation of the compressed air coming from the compression section of the turbomachine.
The pilot cavities 222 are fed with fuel via pilot injectors 22 0a, each opening out radially into one of the cavities. Each full-throttle injector 220b opens out radially into the combustion area between two adjacent pilot cavities.
Each pilot cavity 222 is preferably closed at its upstream end by a radial partition 228, and open at its downstream end (see in particular Figures 2 and 5). Thus, the air that penetrates into the combustion area 216 via its air admission opening 218 does not disturb the flow of air introduced into the pilot cavities 222 via the air injection orifices 226.
The combustion chamber operates as follows: the compressed air coming from the compression section 100 and in rotation about the longitudinal axis X-X penetrates into the combustion section 200. This air is split into two flows: an "internal" flow; and an "external" flow. The external flow goes around the combustion chamber 202 and feeds- the pilot cavities 222 after cooling the outer wall 214 of the combustion chamber and the outer casing 2 04 of the combustion section. This outer air is injected into the pilot cavities via the air injection orifices 226 in the same direction of rotation as the direction of the air entering into the combustion section. In the pilot cavities, the air is mixed and burnt with the fuel injected via the pilot injectors 220a. The inner flow, which represents the major flow, penetrates into the combustion area 216 via the air admission opening 218 where it is mixed and burnt with the fuel injected by thefull-throttle injectors 220b. The combustion flame is stabilized by the "carburation" of the pilot cavities.
Variant embodiments of the combustion chamber of the invention are described below.
In the embodiment of Figures 2 and 3, the longitudinal partition 224 of each pilot cavity that does not have air injection orifices presents, in cross-section, a section that is substantially curvilinear (unlike the other wall which is substantially plane). The curvature of these walls serves to accompany the rotary motion of the air injected into the pilot cavities via the air injection orifices 226.
In contrast, in the variant embodiment of Figure 6, both of the longitudinal partitions 224 defining each pilot cavity 222 circumferentially are substantially plane, each extending in a radial direction.
In general, the number and the geometrical dimensions of the pilot cavities 222 in the combustion chamber can vary depending on requirements. The same applies to the number, the dimensions, and the positioning of the air orifices 226 into said cavities.
As shown in Figure 1, the combustion chamber 202 may also have an inner annular fairing 230 that is mounted on the inner wall 212 extending the upstream end thereof, and also an outer annular fairing 232 that is mounted on the outer wall 214 extending the upstream end thereof. The presence of these fairings 230, 232 serves to control the flow rate of air penetrating into the combustion chamber 202 and the flow rate going round it.
Finally, the outer wall 214 of the combustion chamber may include at its downstream end an annular flange 234 projecting radially outwards from the wall, this flange being provided with a plurality of holes 236 that are spaced-apart regularly around the longitudinal axis X-X for the purpose of feeding cooling air to the turbine section 300.

CLAIMS
1. A turbomachine combustion chamber (202) comprising:
• an inner annular wall (212) about a longitudinal axis (X-X);
• an outer annular wall (214) centered on the longitudinal axis and surrounding the inner wall so as to co-operate therewith to define an annular space (216) forming a combustion area; and
• a plurality of fuel injector systems (220) comprising pilot injectors (220a) alternating circumferentially with full-throttle injectors (220b);
the combustion chamber being characterized in that it further comprises at least one air admission opening (218) opening out into the upstream end of the combustion area in a direction that is substantially longitudinal;
in that the outer wall (214) includes a plurality of pilot cavities (222) that are regularly distributed around the longitudinal axis, each pilot cavity extending longitudinally between the two longitudinal ends of the outer wall and radially towards the outside thereof, the pilot cavities being fed with air from outside the combustion chamber in a common substantially circumferential direction; and
in that each pilot injector (220a) opens out radially into a pilot cavity (222), and each full-throttle injector (220b) opens out radially between said adjacent pilot cavities.
2. A combustion chamber according to claim 1, in which each pilot cavity (222) is closed at its upstream end and open at its downstream end.
3. A combustion chamber according to claim 1 or claim 2, in which each pilot cavity (222) is defined circumferentially by two substantially radial partitions (224), one of the partitions including a plurality of air
injection orifices (226) open to the outside of the combustion chamber and leading to said pilot cavity.
4. A combustion chamber according to claim 3, in which the other partition of each pilot cavity (222) presents in cross-section, a section that is substantially curvilinear.
5. A combustion chamber according to any one of claims 1 to 4, in which the full-throttle injectors (220b) are offset axially downstream relative to the pilot injectors (220a).
6. A combustion chamber according to any one of claims 1 to 5, in which it does not have a wall transversely interconnecting the upstream longitudinal ends of the inner and outer walls (212, 214).
7. A combustion chamber according to any one of claims 1 to 6, in which the fuel injector systems (220) do not have associated air systems.
8. A combustion chamber according to any one of claims 1 to 7, further including an inner annular fairing (230) mounted on the inner wall (212) extending the upstream end thereof, and an outer annular fairing (232) mounted on the outer wall' (214) and extending the upstream end thereof.
9. A turbomachine, characterized in that it includes a combustion chamber (202) according to any one of claims 1 to 8 .