EP1342955A1 - Injection system for air-fuel mixture in a combustion chamber - Google Patents

Abstract

The system for injection of an air/fuel mixture into the combustion chamber of a gas turbine engine includes a fuel injectors which are specifically placed with regard to air injectors. The fuel injector positions ensure that the fuel is injected in a direction perpendicular to air flow. This allows various operating modes for use at different speeds. The system for injection of an air/fuel mixture into the combustion chamber of a gas turbine engine includes a fuel injector situated between first (22) and second (24) air injectors. This is placed in the internal cavity of a venture (26), and includes a first fuel admission circuit (32) and a second fuel admission circuit (34). These are independent and enable a number of different modes of injection of the fuel and air. At least one orifice of the first circuit is formed in a front wall (28) of the venture, in order to inject the fuel in a direction perpendicular to the flow of air from the first air injector. A further orifice (38) in the second circuit is formed in a wall upstream of the venture, in order to inject fuel in a direction perpendicular to the flow of air from the second air injector.

Description

Invention background

The present invention relates to the general field of fuel injection systems in a combustion chamber of a gas turbine engine. It relates more particularly to an injection system of an air / fuel mixture provided with a multi-mode fuel injection making it possible to define at least two independent modes of injection of the air / fuel mixture according to predetermined engine operating regimes. .

In a conventional combustion chamber of a gas turbine engine, the fuel injection is carried out, for each injection system, in a single mode by means of a fuel injector. Two air tendrils centered on the fuel injector each deliver a radial air flow downstream of the fuel injection in order to produce the air / fuel mixture intended to be injected and then burned in the combustion chamber. The air flows from the two tendrils are generally delimited by a venturi interposed between these tendrils and a bowl mounted downstream of them accelerates the flow of the air / fuel mixture towards the combustion chamber.

The air / fuel mixture obtained by such injection systems must be optimal to allow the combustion chamber to ignite, ensure combustion stability, especially at low engine operating speeds, and limit emissions of pollutant releases. in the atmosphere, in particular in the so-called full throttle engine regime. These requirements imply operating modes which are often incompatible with each other. For example, the stability of the combustion flame, necessary in particular at low engine operating speeds, is favored by a heterogeneity of the air / fuel mixture having zones rich in air / fuel mixture close to zones poor in mixture. Conversely, the formation of pollutants, such as nitrogen oxides, is limited by combustion in a lean and homogeneous mixture environment.

A single-mode fuel injection system such as that described above does not correctly fulfill all of the operating requirements listed above. In fact, the fuel injection of these systems takes place in areas where the mass of air introduced is the smallest, which tends to make the air / fuel mixture heterogeneous. Fuel injection reduced to a single point is further optimized for only one or at most two engine operating speeds. In particular, the idling speed of these injection systems is not perfectly guaranteed, which leads to significant levels of carbon monoxide emissions.

In order to overcome these drawbacks, it is known to use combustion chambers with two heads, the principle of which consists in separating the combustions at low and at high speed by providing the chamber with fuel injectors distributed over a so-called “pilot” head. and on a so-called “takeoff” head spaced from the previous one both radially and axially. Although this solution appears satisfactory, a two-headed chamber remains difficult to control and expensive considering the doubling of the number of fuel injectors compared to a conventional single-head combustion chamber.

Also known is American patent US Pat. No. 5,816,049 which proposes a system for injecting an air / fuel mixture, the fuel injection of which is carried out in multiple ways through orifices provided at the level of a venturi delimiting air flows. from a radial spin and an axial spin and through orifices opening into the passage of the air flow from the radial spin. However, the injection system described in this patent also has drawbacks. The fuel supply to the injection orifices takes place in particular through several supply conduits which considerably increases the risks of coking of the fuel. In addition, the particular arrangement of the fuel injection orifices with respect to the air injection involves significant risks of rising fuel.

Subject and summary of the invention

The present invention therefore aims to overcome such drawbacks by proposing an injection system comprising a multi-mode injection of the air / fuel mixture which makes it possible to prepare an optimal air / fuel mixture under low speed and high speed conditions in order to limit polluting emissions. It also targets an injection system which limits the risks of coking and prevents any refueling.

To this end, there is provided a system for injecting an air / fuel mixture into a combustion chamber of a gas turbine engine, the injection system having a longitudinal axis and comprising means for injecting fuel interposed between first and second air injection means, the fuel injection means being arranged in an annular internal cavity of a venturi, the cavity being delimited by a substantially axial upstream wall and by a downstream wall substantially radial, the fuel injection means comprising at least one first fuel intake circuit provided with at least one fuel injection orifice, and a plurality of second fuel intake circuits, independent of the first, each provided with at least one fuel injection orifice so as to define a plurality of independent modes of injection of the air / fuel mixture according to determined engine operating speeds, the syst th of injection being characterized in that the fuel injection orifice of the first fuel intake circuit is formed in the upstream wall of the venturi in order to inject fuel towards the combustion chamber in a general direction substantially perpendicular to a flow of air from the first air injection means, and in that the fuel injection orifices of the second fuel intake circuits are formed in the downstream wall of the venturi in order to inject fuel towards the combustion chamber in a general direction substantially perpendicular to an air flow from the second air injection means.

In this way, the injection system makes it possible both to generate a homogeneous and lean air / fuel mixture at high speed conditions in order to limit the polluting emissions of nitrogen oxides, and to create gas pockets in proportion stoichiometric at low conditions speed to guarantee the ignition and stability of the combustion flame in the chamber while controlling carbon monoxide emissions. The injection of the air / fuel mixture is carried out in a multi-mode manner according to the operating conditions of the engine. The distribution of fuel in the injection system can thus be perfectly controlled as a function of the mass of air introduced by the air injection means. In addition, the injection of fuel in directions perpendicular to the air flows from the air injection means improves the homogenization of the air / fuel mixture.

Advantageously, the fuel injection orifices of the first and second fuel intake circuits are regularly distributed around the longitudinal axis and have angular positions offset with respect to each other in order to improve the homogenization of the mixture.

A single supply conduit makes it possible to supply fuel to the first and second fuel intake circuits, for example via a plurality of concentric tubes. Thus, the fuel supply is carried out by a single conduit which limits the risks of coking by taking advantage of the cooling obtained by the circulation of the fuel in the circuits.

Additional means for injecting air or fuel centered on the longitudinal axis of the injection system advantageously make it possible to define additional modes of injecting the air / fuel mixture. These means are mounted on a bowl centered on the longitudinal axis and extending downstream from the first air injection means.

Brief description of the drawings

• la figure 1 est une vue en coupe et partielle d'une chambre de combustion équipée de systèmes d'injection selon un exemple de réalisation de l'invention ;
• la figure 2 est une vue partielle et agrandie d'un système d'injection de la figure 1 ;
• la figure 3 est une vue en perspective et en écorché d'un système d'injection de la figure 1 ; et
• la figure 4 est une vue schématique de face d'un système d'injection selon un autre exemple de réalisation de l'invention.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures:

• Figure 1 is a sectional and partial view of a combustion chamber equipped with injection systems according to an exemplary embodiment of the invention;
• Figure 2 is a partial and enlarged view of an injection system of Figure 1;
• Figure 3 is a perspective and cutaway view of an injection system of Figure 1; and
• Figure 4 is a schematic front view of an injection system according to another embodiment of the invention.

Detailed description of an embodiment

Reference is made to FIG. 1 which partially illustrates and in section a combustion chamber 10 equipped with a plurality of systems for injecting an air / fuel mixture 12. The combustion chamber 10 is hung on an external casing 14 by fixing means not shown. It is for example of the annular type and is delimited by two annular walls 16, 18 connected upstream by an annular chamber bottom 20. The chamber bottom 20 comprises a plurality of openings regularly spaced circularly around an axis 21 of the gas turbine engine equipped with such a combustion chamber. An injection system 12 according to the invention is mounted in each of these openings. The injection systems prepare an air / fuel mixture intended to be burned in the combustion chamber 10. The gases resulting from this combustion flow downstream in the chamber before supplying a high pressure turbine.

As more particularly illustrated by FIG. 2, the injection system 12, of longitudinal axis X-X, comprises fuel injection means interposed between first and second air injection means. These first and second air injection means are preferably constituted respectively by internal 22 and external 24 tendrils arranged radially with respect to the longitudinal axis X-X. These air tendrils, of a type known per se, therefore each deliver an air flow in a substantially radial direction. The external spin 24 is mounted so as to be offset radially with respect to the internal spin 22.

The fuel injection means are mounted in an annular internal cavity of an annular venturi 26 centered on the longitudinal axis XX of the injection system and delimiting the air flows from the internal 22 and external 24 gimlets. The venturi includes an upstream wall 28 extending in a substantially axial direction from the internal spin 22 and extending by a substantially radial downstream wall 30 connected to the external spin 24.

The fuel injection means comprise at least a first fuel intake circuit 32 and a plurality of second fuel intake circuits 34. These first and second circuits are independent of each other and are in particular delimited by the upstream 28 and downstream 30 walls of the venturi 26. For reasons of convenience of representation, the fuel injection means illustrated in FIGS. 1 to 3 comprise a single first and only one second fuel intake circuits. Of course, it is conceivable that these injection means comprise several first and second circuits.

The first fuel intake circuit 32 opens towards the combustion chamber 10 in a generally radial direction through at least one fuel injection orifice 36 formed in the upstream wall of the venturi. The second fuel intake circuits 34 open towards the combustion chamber 10 in a generally axial direction generally via at least one fuel injection orifice 38 formed in the downstream wall of the venturi. Thus, in accordance with the invention, the fuel present in the first fuel intake circuit 32 is injected into the flow of the air flow generated by the internal spin 22 in a general direction substantially perpendicular to this flow. Likewise, the fuel present in the second fuel intake circuits 34 is injected into the flow of the air flow generated by the external spin 24 in a general direction substantially perpendicular to this flow. As an example, six fuel injection orifices can be provided per fuel intake circuit.

According to an advantageous characteristic of the invention, the fuel injection orifices 36, 38 of the first and second fuel intake circuits 32, 34 are distributed regularly all around the longitudinal axis XX of the injection system, and the orifices 36 of the first circuits have angular positions offset with respect to the orifices 38 of the second circuits. This characteristic makes it possible to improve the homogeneity of the air / fuel mixture. In addition, the injection ports fuel are preferably not arranged opposite the air outlets of the inner and outer tendrils.

The presence of at least a first and a plurality of second independent fuel intake circuits each provided with at least one fuel injection orifice makes it possible to define a plurality of independent modes of injection of the air / fuel according to determined engine operating speeds. For example, in the case of fuel injection means comprising a single first and a single second fuel intake circuit as illustrated in FIGS. 1 to 3, a fuel injection carried out by the first circuit 32 may correspond to a engine idle speed, while a fuel injection performed by the first and second circuits may be suitable for a full throttle engine speed.

According to another exemplary embodiment of the invention illustrated diagrammatically in FIG. 4, there are provided two first fuel intake circuits 32a, 32b and two second fuel intake circuits 34a, 34b. The first fuel intake circuits 32a, 32b each have three fuel injection holes 36a, 36b and the second fuel circuits 34a, 34b each also have three fuel injection holes 38a, 38b so that this system injection 12 allows sixteen independent modes of injection of the air / fuel mixture to be defined. In this figure, it is also noted that the fuel injection orifices 36a, 36b, 38a and 38b of the first and second fuel intake circuits are distributed regularly all around the longitudinal axis XX of the injection system and that 'they have angular positions offset from each other so as to promote the air / fuel mixture.

According to yet another embodiment not shown in the figures, sixteen first and sixteen second fuel intake circuits can be provided, these circuits each being provided with two fuel injection orifices. In this way, these fuel injection means make it possible to define 256 independent modes of injection of the air / fuel mixture.

In Figures 1 and 2, we note that the injection system 12 according to the invention further comprises at least one radial supply duct 40 supplying fuel to both the first and second fuel intake circuits 32, 34. This supply duct 40 advantageously comprises a plurality of tubes, for example concentric, each supplying a fuel intake circuit. In the case illustrated in FIG. 2, the supply duct comprises two tubes 42, 44. More specifically, a first central tube 42 of the duct supplies fuel to the second fuel intake circuit 34, the latter preferably having a torus shape (Figure 3). A second conduit 44, concentric to the first, supplies fuel to the first circuit 32. In the case of several first and several second fuel intake circuits, as many concentric tubes are provided as there are circuits. Thus, the fuel supply to the fuel intake circuits takes place through a single conduit 40 which limits the risks of coking of the fuel. Alternatively, it can be envisaged that the fuel supply conduits are parallel and independent from each other.

The fuel present in the fuel intake circuits is protected from hot gases from the combustion of the air / fuel mixture by means of thermal screens 46 notably interposed between the circuits 32, 34 and the upstream walls 28 and downstream 30 of the venturi 26. The fuel which circulates in the fuel intake circuits also makes it possible to cool the walls of the venturi. In the case of several first and several second fuel intake circuits, the heat shields can also be used to separate the different circuits from each other.

According to another advantageous characteristic of the invention, the injection system further comprises additional means 48 for injecting air or fuel (shown in dotted lines in FIG. 2) centered on its longitudinal axis XX. These additional injection means 48 thus make it possible to define additional modes of injection of the air / fuel mixture. For example, in the case of additional fuel injection means, the fuel injection carried out only by these means may correspond to an engine idling speed, and the fuel injection carried out both by these additional means and through the orifices of the first fuel intake circuits can be suitable for a whole range of intermediate speeds. Finally, a fuel injection by additional means and by the orifices of the first and second circuits may coincide with a full throttle speed of the engine.

Preferably, the additional means 48 for injecting air or fuel are mounted on a bowl 50 centered on the longitudinal axis X-X and extending downstream from the first air injection means. In the case of additional fuel injection means, these consist for example of a conventional fuel injector passing through a wall 52 of the bowl 50 forming the bottom. Similarly, when it comes to additional air injection means, these can be formed by a conventional air spin also passing through the wall 52 of the bowl forming the bottom.

Finally, it can also be noted that a mixing tube 54 is disposed downstream of the external spin 24. This mixing tube has a wall 56 converging downstream and ending in a substantially radial wall 58 extending into the chamber combustion chamber by a deflector 60. This tube makes it possible to accelerate the flow of the air / fuel mixture towards the combustion chamber and to prevent the combustion flame from going upstream.

Claims (11)

Injection system (12) of an air / fuel mixture into a combustion chamber (10) of a gas turbine engine, said injection system having a longitudinal axis (XX) and comprising injection means fuel interposed between first (22) and second air injection means (24), said fuel injection means being disposed in an annular internal cavity (32, 34) of a venturi (26), said cavity being delimited by a substantially axial upstream wall (28) and by a substantially radial downstream wall (30), said fuel injection means comprise at least a first fuel intake circuit (32) provided with at least a fuel injection port (36), and a plurality of second fuel intake circuits (34), independent of the first, each provided with at least one fuel injection port (38), so as to define a plurality of independent modes of injection of the air / fuel mixture according to re determined engine operating modes, said injection system being characterized in that the fuel injection orifice (36) of the first fuel intake circuit is formed in the upstream wall of the venturi in order to inject fuel towards the combustion chamber in a general direction substantially perpendicular to an air flow coming from the first air injection means (22), and in that the fuel injection orifices (38) of the second circuits fuel intake is made in the downstream wall of the venturi in order to inject fuel towards the combustion chamber in a general direction substantially perpendicular to an air flow coming from the second air injection means (24). System according to claim 1, characterized in that the fuel injection orifices (36, 38) of said first and second fuel intake circuits (32, 34) are distributed regularly all around said longitudinal axis. System according to one of claims 1 or 2, characterized in that the fuel injection orifice (36) of said first fuel intake circuit (32) has an angular position offset by relative to the fuel injection orifices (38) of said second fuel intake circuits (34). System according to any one of Claims 1 to 3, characterized in that the second fuel intake circuits (34) have the shape of a torus. System according to any one of Claims 1 to 4, characterized in that it also comprises at least one radial supply duct (40) supplying fuel to the first and second fuel intake circuits (32, 34) . System according to claim 5, characterized in that the supply duct comprises a plurality of concentric tubes (42, 44) each supplying a fuel intake circuit. System according to any one of Claims 1 to 6, characterized in that it further comprises additional air injection means (48) centered on the longitudinal axis (XX) of the injection system. System according to any one of Claims 1 to 6, characterized in that it further comprises additional fuel injection means (48) centered on the longitudinal axis (XX) of the injection system. System according to one of claims 7 or 8, characterized in that said additional injection means are mounted on a bowl (50) centered on said longitudinal axis and extending downstream from the first injection means d air (22). System according to any one of Claims 1 to 9, characterized in that the first (22) and second air injection means (24) are arranged radially with respect to said longitudinal axis. System according to any one of claims 1 to 10, characterized in that the first and second air injection means are constituted respectively by an internal twist (22) and by an external twist (24).

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