Patent Grant
7568345
The present invention relates to the general field of systems for injecting an air/fuel mixture into a turbomachine combustion chamber. It relates more particularly to a fuel injector for an injection system of the aero-mechanical type provided with means for atomizing the fuel prior to mixing with air.
The conventional process for designing and optimizing a turbomachine combustion chamber seeks mainly to reconcile implementing the operational performance of the chamber (combustion efficiency, stability domain, ignition and re-ignition domain, lifetime of the combustion area, etc.) as a function of the intended mission for the airplane on which the turbomachine is mounted, while minimizing emissions of pollution (nitrogen oxides, carbon monoxide, unburnt hydrocarbons, etc.). To do this, it is possible in particular to act on the nature and the performance of the injection system for injecting the air/fuel mixture into the combustion chamber, on the distribution of dilution air inside the chamber, and on the dynamics of air/fuel mixing within the chamber.
The combustion chamber of a turbomachine typically comprises an injection system for injecting an air/fuel mixture into a flame tube, a cooling system, and a dilution system. Combustion takes place mainly within a first portion of the flame tube (referred to as the “primary zone”) in which combustion is stabilized by means of air/fuel mixture recirculation zones induced by the flow of air coming from the injection system. In the second portion of the mixer tube (referred to as the “dilution zone”), the chemical activity that takes place is less intense and the flow is diluted by means of dilution holes.
In the primary zone of the flame tube, various physical phenomena are involved: injection and atomization into fine droplets of the fuel, evaporation of the droplets, mixing of fuel vapor with air, and chemical reactions of fuel being oxidized by the oxygen of the air.
These physical phenomena are governed by characteristic times. Atomization time thus represents the time needed by the air to disintegrate the sheet of fuel and form an air/fuel spray. It depends mainly on the performance and the technology of the injection system used and on the aerodynamics in the vicinity of the sheet of fuel. Evaporation time also depends on the injection system used. It is a function directly of the size of the droplets resulting from the disintegration of the sheet of fuel; the smaller the droplets, the shorter the evaporation time. Mixing time corresponds to the time needed for the fuel vapor coming from evaporation of the droplets to mix with the air. It depends mainly on the level of turbulence within the combustion area, and thus on the flow dynamics in the primary zone. Chemical time represents the time needed for the chemical reactions to develop. It depends on the pressures and temperatures at the inlet to the combustion area and on the nature of the fuel used.
The injection system used thus plays a fundamental role in the process of designing a combustion chamber, in particular when optimizing the times that are characteristic of fuel atomization and evaporation.
There exist two main families of injection systems: “aero-mechanical” systems in which the fuel is atomized as a result of a large pressure difference between the fuel and the air; and “aerodynamic” systems in which the fuel is atomized by being sheared between two sheets of air. The present invention relates more particularly to systems of the aero-mechanical type.
Aero-mechanical injection systems known in the prior art present numerous drawbacks. In particular, the pressure limitation does not enable the size of fuel droplets to be reduced sufficiently. Furthermore, the air/fuel spray created by such injection systems is not always stable at all operating speeds of the engine.
A main object of the present invention is thus to mitigate such drawbacks by proposing an injector for an aero-mechanical injection system that enables the times characteristic of fuel atomization and evaporation to be reduced under all operating speeds of the turbomachine.
To this end, the invention provides a fuel injector for an aero-mechanical injection system for injecting an air/fuel mixture into a turbomachine combustion chamber, the injector comprising: a main tubular structure of axis XX′ opening out at a downstream end for delivering the air/fuel mixture; a tubular fuel duct disposed inside the main structure so as to co-operate therewith to form an annular passage, and opening out at a downstream end into the main structure via a fuel atomizer plug so as to introduce fuel at a pressure PC into the main structure; and at least one air feed channel connected to a compressor stage of the turbomachine and opening out into the annular passage in such a manner as to introduce air at a pressure PA into said passage, the injector further comprising means for injecting a gas into the fuel duct, the gas being at a pressure PG that is greater than PA and greater than or equal to PC, in order to create effervescence in the fuel while it is being introduced into the main structure.
Injecting gas into the fuel duct at a pressure that is greater than or equal to the pressure of the fuel creates a liquid/gas mixture at the pressure PC prior to its introduction into the main structure in which it will be dispersed. As this mixture expands from the pressure PC to the internal pressure within the main structure, the sudden expansion of the gaseous phase causes the sheet of fuel to disintegrate: this is referred to as effervescence. As a result, the times characteristic of the fuel atomizing and evaporating at the outlet from the injection system can be reduced considerably.
At low operating speeds of the turbomachine, these shorter times enable combustion efficiency to be improved and increase the ability of the combustion area to avoid going out, and at full-throttle operating speed of the turbomachine they serve to limit the formation of polluting emissions of the nitrogen oxide and soot types.
More particularly, the injector includes a tubular gas duct which is disposed inside the fuel duct and has a plurality of orifices opening out into the fuel duct.
Advantageously, the orifices of the gas duct open out substantially perpendicularly into the fuel duct and they are disposed in at least one common transverse plane.
The fuel atomizer plug may comprise a cylindrical portion centered on the axis XX′, having an outside diameter that is smaller than the inside diameter of the fuel duct, and provided with a plurality of profiled fins extending radially outwards, said fins having outside surfaces coming into contact with an inside surface of the fuel duct.
Preferably, the profiled fins of the fuel atomizer plug are distributed regularly over the entire circumference of the cylindrical portion. They may be twisted angularly, preferably by about 45°, in the same direction.
In an embodiment of the invention, the orifices of the gas duct open out into the fuel duct through the fuel atomizer plug.
More particularly, the orifices of the gas duct open out between pairs of adjacent fins of the fuel atomizer plug and open out tangentially into the gas duct.
In another embodiment of the invention, the orifices of the gas duct open out into the fuel duct upstream from the fuel atomizer plug.
According to an advantageous characteristic of the invention, a device is provided for controlling the flow rate of the gas injected into the fuel duct.
The present invention also provides an aero-mechanical injection system fitted with a fuel injector as defined above.
Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings which show an embodiment that has no limiting character. In the figures:
With reference to
A tubular fuel duct 6 is disposed inside the main structure 4 so as to co-operate therewith to form an annular passage 8. The tubular duct 6 which is centered on the axis XX′ opens out at a downstream end inside the main structure 4 via a fuel atomizer plug 10, 10′. Its downstream end may also be substantially conical in shape.
The fuel atomizer plug 10, 10′ serves to introduce fuel at a pressure PC, e.g. of about 4 bar to 80 bar, into the main structure 4 at its downstream end 4a. Its main function is to cause the fuel to be dispersed in the form of a plurality of jets (or tubes) of fuel.
The fuel injector 2, 2′ further comprises at least one air feed channel 12 that is connected to a compressor stage (not shown) of the turbomachine and that opens out into the annular passage 8 so as to introduce air therein at a pressure PA, e.g. of the order of 0.5 bar to 50 bar.
In the embodiments shown in
An air swirler 14 can be disposed in the annular passage 8 between the upstream and downstream ends 4a and 4b of the main structure 4. Such an air swirler 14 serves to impart a rotary effect (or “swirl”) to the flow of air in the annular passage 8.
The air flowing in the annular passage 8, optionally caused to swirl by the air swirler 14, then comes to break up the jets of fuel created by the fuel atomizer 10, 10′ in the vicinity of the downstream end 4a of the main structure 4. Under the combined effect of the fuel atomizer 10, 10′ and of the air flowing in the annular passage 8, an air/fuel spray is created at the outlet from the injector.
According to the invention, the fuel injector 2, 2′ further comprises means for injecting a gas into the fuel duct 6, which gas is at a pressure PG that is greater than the pressure PA and greater than or equal to the pressure PC, so as to create effervescence in the fuel on being introduced into the main structure 4.
More particularly, a tubular gas duct 16 is disposed inside the fuel duct 6 and has a plurality of orifices 18 opening out into the fuel duct 6. The gas duct 16 is likewise centered on the axis XX′ and co-operates with the fuel duct 6 to form an annular passage 20 for the flow of fuel.
Introducing gas into the fuel duct 6 at a pressure PG greater than the pressure PA and greater than or equal to the pressure PC serves to create a liquid/gas mixture at the pressure PC prior to its introduction into the main structure 4. The effervescence of the fuel is characterized by the fuel atomizing as the result of the gas expanding suddenly on being introduced into the main structure 4. The times characteristic of fuel atomization and evaporation are thus shortened.
More particularly, fuel effervescence occurs when the following conditions are satisfied: the gas must be at a pressure PG that is at least substantially equal to the pressure PC of the fuel (or at a pressure that is slightly greater than that), and liquid/gas mixing must take place in a space that is substantially confined so that the mixture is at the pressure PC (specifically, mixing takes place in the zone of confluence between the orifices 18 and the fuel duct 6 into which they open out).
The gas is preferably an inert gas that has no direct influence on the subsequent combustion of the air/fuel mixture. For example the gas may be air taken from a compressor stage of the turbomachine and that is further compressed in order to reach a pressure PG greater than the pressure PA of the air being fed to the air feed channels 12.
According to an advantageous characteristic of the invention, the orifices 18 of the gas duct 16 open out substantially perpendicularly into the fuel duct 6. This particular arrangement serves to encourage the appearance of effervescence in the fuel.
Alternatively, the orifices 18 may slope downstream relative to the axis XX′, e.g. at about 60°.
According to another advantageous characteristic of the invention, the orifices 18 of the gas duct 16 are disposed in at least one common transverse plane (in two transverse planes in
As shown in
The profiled fins 24 together present an outside surface that comes into contact with an inside surface of the fuel duct 6 (
The fins 24 of the fuel atomizer plug 10 may be distributed regularly over the entire circumference of the cylindrical portion 22. They may also be twisted in a common direction, i.e. they may present angular twists in the same direction. Together they thus form threading.
The angular twist of the fins 24 is preferably about 45° relative to the axis XX′. This angular twist serves to create a swirl effect in the flow of fuel, and more particularly in the fuel jets, at the outlet from the fuel atomizer 10.
Furthermore, when the fuel injector 2, 2′ includes an air swirler 14 disposed in the annular passage 8, the angular twist of the fins 24 is advantageously in the same direction as that of the swirler 14.
According to yet another advantageous characteristic of the invention, the injector system 2, 2′ further comprises a device 28 for controlling the flow rate of the gas injected into the fuel duct 6. Such a device 28 thus serves to control the rate at which gas needs to be injected for the purpose of causing effervescence in the fuel. For example, the gas flow rate may be controlled as a function of the flow rate and the pressure PC of the fuel.
Particular features of the fuel injector 2 shown in
In this embodiment, the orifices 18 of the gas duct 16 open out into the fuel duct 6 through the fuel atomizer plug 10. To this end, the gas duct 16 extends axially as far as the atomizer plug 10 to which it is secured. The atomizer plug 10 may present a hollow cavity into which the gas duct 16 opens out, with the cavity leading to the orifices 18. Alternatively, the gas duct 16 and the atomizer plug could be made as a single piece.
More particularly, the orifices 18 of the gas duct 16 open out between pairs of adjacent fins 24 on the fuel atomizer plug 10, i.e. they open out into the grooves 26 in which the fuel jets form. As a result, the mixing between the fuel of the gas takes place in the zone of confluence between the orifices 18 and the grooves 26, and the resulting effervescence in the fuel causes the jets of fuel to disintegrate into fine drops.
As shown in
The particular features of the fuel injector 2′ shown in
In this embodiment, the orifices 18 of the gas duct 16 open out into the fuel duct 6 upstream from the fuel atomizer plug 10′. The gas duct 16 extends axially as far as the atomizer plug 10′ and it is secured thereto (or it may form a single piece therewith).
The orifices 18 may be arranged in two transverse planes. Thus, mixing between the fuel of the gas takes place in the zone of confluence between the orifices 18 and the zone of the gas duct 16 into which the orifices open out. Mixing between the liquid and the gas takes place before the mixture is dispersed in the form of jets via the atomizer plug 10′.
Still in this embodiment, it should also be seen in
The fuel injector 2, 2′ as described above is appropriate for aero-mechanical injection systems for injecting an air/fuel mixture into a turbomachine combustion chamber.
The injection system 100 shown in
A Venturi 106 presenting an internal throat of convergent and divergent shape is interposed between the inner and outer air swirlers 102 and 104. It serves to mark the boundary between the flows of air coming from the air swirlers 102 and 104.
A bowl 108 that is flared downstream is mounted downstream from the outer air swirler 104. By means of its opening angle, the bowl 108 serves to distribute the air/fuel mixture over the primary zone of the combustion area.
The injection system 200 shown in
The injection system 200 includes a fuel injector 2, 2′ of the invention centered on its axis ZZ′. It has an inner air swirler 202 disposed downstream from the injector 2, 2′ serving to inject air in a radial direction, and an outer air swirler 204 disposed downstream from the inner air swirler 202 and serving to inject air in a radial direction.
A first Venturi 206 is interposed between the air injectors 202 and 204, and a second Venturi 208 is disposed downstream from the outer air swirler 204. A pre-mixer and/or pre-vaporization tube 210 is also disposed downstream from the second Venturi 208.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04 10051 | Sep 2004 | FR | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20060059915 A1 | Mar 2006 | US |
