FR3097298A1 - CANDLE INTEGRATED INTO THE FLAME HOLDER - Google Patents

Abstract

Title: Spark plug integrated into the flame-holder arm The present invention relates to a post-combustion device (100) for a turbojet, configured to extend at least partially within a gas stream (V) of a turbojet, the device for post-combustion (100) comprising: - a flame-holder arm (120) comprising a gutter (122) extending in a longitudinal direction (B) defining an enclosure (E) open downstream, the gutter (122) being configured to form an obstacle in the flow of the primary gas stream (F1), - a spark plug (170), the device being characterized in that the spark plug (170) is positioned at least partially in the enclosure (E). Figure for the abstract: Fig. 6

Description

Candle integrated into the flame holder arm

FIELD OF THE INVENTION

The present invention relates to the field of turbojets with a system for reheating the flow of primary gas (also called a postcombustion device), comprising a flame holder device and in particular a flame holder arm.

STATE OF THE ART

So-called "post-combustion" turbojet engines generally comprise, from upstream to downstream in the direction of gas flow, one or more compressor stages, a combustion chamber, one or more turbine stages, a reheat channel (or post-combustion channel), and an exhaust nozzle. Downstream of the turbine stages, in the reheat channel, the gas flow can undergo a new combustion, thanks to the oxygen still present within it, before expanding in the exhaust nozzle.

At the entrance to the postcombustion channel, flame holders extend within the gas stream. FIG. 1 represents a postcombustion channel 1 of a prior art turbojet engine, located just downstream of the last blade 2 of the turbine. The heating channel 1 is delimited by an annular casing 1", called the postcombustion casing 1". In this case, a so-called confluence shell 1' delimits, with the afterburner casing 1", a passage for the cooling air coming from the secondary air flow F2, the primary gas flows F1 and secondary F2 being here mixed downstream of the confluence shroud 1′. By external and internal, we mean external and internal with respect to the axis A′ of the turbojet engine.

At the inlet of the post-combustion channel 1 extend radially arms 3 fuel injectors, integral with the confluence shell 1 'and the post-combustion casing 1 ". The function of the injector arms 3 is to vaporize fuel in the direction of the hook arm -flames 4, located downstream in the afterburner channel 1.

Close to the confluence shroud 1', here in the primary flow F1, the flame holder arms 4 support a peripheral flame holder ring 5 . This flame holder ring 5 consists of a plurality of ring portions, typically nine in number, which extend, concentrically to the ferrule 1' and to the casing 1" of the heating channel 1, between two hanging arms -flames 4. The flame holder ring 5 performs the same function as the flame holder arms 4, namely, a flame stabilization function. In Figure 1 , the arms 4 are supplied with fuel but the ring Flame Hanger 5 is not.

With particular reference to Figure 2, which is a sectional view of the flame holder arm 4 according to AA of Figure 1 , each flame holder arm 4 comprises a gutter 6, of U-shaped section open on the downstream side, whose function is to form an obstacle in the flow of the primary gas flow to generate gas recirculation zones, which stabilize the flames.

The flames are thus "hooked" on the arm 4. The gutter 6 is moreover the structural element of the arm 4, the other elements of the latter being attached to it. A fuel supply rail 7 can be provided and can extend along each arm 4, inside the gutter 6. The fuel supply of the flame-holder devices makes it possible to obtain an adaptable combustion and better efficiency, because fuel is injected both at the level of the fuel injector arms 3, from where it is vaporized in the direction of the flame-holder arms 4, and at the level of the flame-holder arms 4, from where it is is injected directly into the flame stabilization zone.

Each arm 4 also comprises a ventilation box 8, extending radially from the upstream side of the gutter 6, that is to say on the side of the base of the V, upstream from the tube 7 for supplying fuel. Such a ventilation box 8 has the function of cooling the walls of the gutter 6, as well as cooling the tube 7 for fuel injection; for this, the box 8 is supplied with cooling air and comprises a plurality of perforations through which the cooling air is projected against the elements to be cooled.

Cooling the injection tube 7 is useful even in the absence of afterburner, because it prevents fuel residues from entering a coking process on the tube 7.

Each arm 4 comprises, downstream of the fuel injection tube 7, a protection screen 9 (or heat shield), with a V-section, the function of which is to protect the fuel injection tube 7, the cooling 8 and the gutter 6 against the flames attached to the trailing edges of the walls of the gutter 6. This screen 9 occupies almost all the space between the downstream end of the walls of the gutter 6. The fuel, schematized by the arrows 10 , is propelled against the walls of the gutter 6 and evacuated between these walls and the protective screen 9, in order to participate in the combustion.

The description which has just been made in relation to the arms 4 is entirely transposable to a flame holder ring (or to portions of a ring). The cross-sectional view of FIG. 2 may correspond to a cross-sectional view, not of a rectilinear radial flame-holder device (an arm), but of a curvilinear annular flame-holder device (a flame-holder ring or a flash holder ring portion). A person skilled in the art will easily transpose. In Figure 1 , the ring 5 is not supplied with fuel.

Such a flame holder device is described in particular in the documents FR2909438 and FR2942640.

According to other configurations, the flame holder arm 4 does not include an injection tube; in this case, it fulfills its function of stabilizing the flames but not that of supplying the flames with fuel. Such a flame holder device is described in particular in the documents EP1840469.

In order to ignite the mixture, a candle is needed. The spark plug is usually mounted on the flame holder ring and exits inside the flame holder ring near the fuel supply tube. This candle is described in detail in the documents FR2942640 and EP1621817.

Furthermore, the flame holder ring is positioned most of the time in the secondary gas flow, even if it can sometimes be in the primary gas flow. Document EP1621817 describes this.

The ignition of the postcombustion is therefore generally initiated in a flame holder ring bathed in the secondary flow, i.e. a cold flow. The ignition range and the ignition probabilities are restricted there.

The document FR3039220 proposes a structure that is notoriously different from the existing post-combustion devices, with a nozzle 14 integrated in a flame holder ring 4 located at the level of the primary gas flow, downstream of which is positioned a spark plug 15 for the post-combustion. The spark plug 15 is then mounted via an orifice in the flame holder ring 5. FIG. 3 illustrates the solution proposed by this document.

Nevertheless, it is necessary here to completely review the structure of the flame holder arm in order to set up a specific nozzle there. In addition, the location of the candle in the flame holder ring, in the middle of the combustion chamber, can pose difficulties.

An object of the invention is to solve both the existing ignition difficulties, while keeping an architecture close to that existing to limit the modifications to be made.

To this end, a postcombustion device for a turbojet engine is proposed, configured to extend at least partially within a gas stream of a turbojet engine, the postcombustion device comprising:
- a flame holder arm comprising a gutter extending in a longitudinal direction defining an enclosure open downstream, the gutter being configured to form an obstacle in the flow of primary gas flow,
- a candle,
the device being characterized in that the candle is positioned at least partially in the enclosure.

Ignition therefore takes place in the primary flow, which is a hotter environment than the secondary flow F2, which increases the ignition domain and the ignition probabilities in this domain.

More precisely, the spark plug comprises electrodes, the electrodes being positioned in the enclosure. The candle also includes a body, which makes up most of the volume of the candle. Preferably only the electrodes are positioned in the enclosure, that is to say that the body of the candle, or the major part of the body of the candle, is located outside the enclosure.

In one embodiment, the gutter has a V-shaped section, open on the downstream side. The base of the V is advantageously rounded.

Preferably, the flame holder arm is a so-called radial arm, which means that the flame holder arm passes through a plane containing the turbojet axis.

In one embodiment, the flame holder arm further comprises a protective screen extending in the longitudinal direction and separating the enclosure into a confined space and an open space, in which the candle is positioned at least partially in the 'open space. The electrodes are then positioned in the open space.

In one embodiment, the protective screen comprises a plurality of free orifices, to allow the air-fuel mixture to escape from the confined space into the open space.

In one embodiment, the protective screen has a V-shaped section, open on the downstream side. The base of the V is advantageously rounded.

In one embodiment, the protective screen has a curved shape partially surrounding the spark plug, more precisely the electrodes of the spark plug.

In one embodiment, the flame holder arm further comprises a fuel injection rail extending in the longitudinal direction in the enclosure.

In one embodiment, the fuel injection rail extends in the longitudinal direction along a diffusion length longer than half the length of the gutter and includes a plurality of diffusion ports for supplying fuel to the flame holder arm on the diffusion length.

In one embodiment, the candle extends a candle length between 5 and 20% of the length of the flame holder arm, for example between 10 and 15%.

In one embodiment, the postcombustion device further comprises a flame holder ring, located at one end of the flame holder arm, the postcombustion ring comprising two wings, the two wings comprising passage openings and/or notches to allow the passage of a body of the candle (170).

In one embodiment, the flame holder arm further comprises a ventilation (or cooling) ramp box extending in the longitudinal direction in the enclosure, the ventilation ramp comprising an inlet located at a radially outer end and configured to capture air from the secondary flow and including a plurality of vents, configured to allow air to be exhausted to the enclosure.

Finally, the invention proposes a turbojet comprising a post-combustion device as described above.

DESCRIPTION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

FIG. 1 illustrates a first post-combustion device known from the prior art, with in particular a flame holder arm.

Figure 2 illustrates a sectional view along AA of the flame holder arm of Figure 1.

FIG. 3 illustrates a second post-combustion device known from the prior art.

FIG. 4 schematically illustrates a post-combustion device according to one embodiment of the invention.

FIG. 5 schematically illustrates a post-combustion device according to one embodiment of the invention.

FIG. 6 illustrates a view in section of a post-combustion device according to FIG. 4 or 5, at the level of the spark plug (more precisely of the electrodes).

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figures 4 to 6 , an afterburner 100 will be described. It is mounted on a turbojet as described in the introduction, with a secondary stream and a primary stream. A longitudinal direction A′ is defined at the turbojet, which corresponds to a direction of rotation of the turbine and a radial direction, extending orthogonally to the longitudinal direction.

The following elements are similar to those presented in FIG. 1 in particular: the turbojet with an axis A′, a turbine blade 2, a fuel injector arm 3, an annular casing 110, called postcombustion casing, a confluence shroud 114 which separates the primary stream F1 and the secondary stream F2.

The afterburner 100 includes a flame holder arm 120, mounted on the afterburner casing 110 which defines an afterburner chamber of a turbojet, at its radially outer end. The flame holder arm 120 extends inside a vein V of the turbojet engine along a longitudinal direction B. The longitudinal direction B passes through the axis A' of the turbojet engine, which means that the arm -flame passes through a plane containing the axis A' of the turbojet engine. The radially inner end of the flame holder arm 120 is located downstream relative to the radially outer end, depending on the direction of gas flow in use.

A plurality of post-combustion devices 100 are provided: they are distributed along the circumference of the post-combustion casing 110. There can be nine of them, for example, distributed every 40°. The description will be made for a single afterburner 100.

Advantageously, the postcombustion device 100 comprises a flame holder ring 130, placed peripherally in the vein V. It can comprise several ring sections placed end to end; typically there are as many portions as there are flame holder arms 120. The flame holder ring 130 comprises two wings forming an opening downstream, like a gutter 122 of flame holder arms (which will be described below). The flame holder ring 130 has the same function as the flame holder arm 120 and it advantageously comprises a fuel rail (not visible in FIGS. 4 to 6). In FIGS. 4 and 5 , the flame holder ring 130 is placed in the secondary flow F2, but it can be moved in the primary flow F1.

At secondary flow F2, flame holder arm 120 may include an aerodynamically shaped shroud at the radially outer location where flame holder arm 120 attaches to afterburner housing 110.

The flame holder arm 120 comprises a gutter 122 defining an enclosure E open downstream. The function of such a flame holder arm 120 is to obstruct the flow of the primary gas flow F1 to generate gas recirculation zones, which stabilize the flames. The gutter 122 extends along the longitudinal direction B. Except at its ends, the gutter 122 has a V-section with two wings 122a, 122b which diverge downstream to form two ejection springboards for sprayed fuel. In other words, to define the enclosure E, except at its radial ends, the gutter 122 has substantially (with the curvatures close in particular, and in particular the base where the shape is generally rounded) an open dihedral shape with the two wings 122a, 122b and whose intersection line extends along the longitudinal direction B.

The enclosure E is therefore the volume defined inside the gutter 122, between the two wings 122a, 122b (if the end of the two wings 122a, 122b were closed by a flat surface, the enclosure E would then correspond to volume shut in).

The flame holder arm 120 further comprises a fuel injection ramp 140 which extends along the longitudinal direction B inside the gutter 122, in the enclosure E. This is a ramp and not a jet because it allows the fuel to be diffused more widely using several ejection points. To distinguish it from a nozzle or other localized injection means, a diffusion length is defined for it which is longer than half the length of the gutter 122 in the longitudinal direction B. in a fuel injection pipe make it possible to produce the injection rail 140.

The flame hanger arm 120 also comprises a ventilation box 150 (or cooling box), which extends along the longitudinal direction B inside the gutter, in the enclosure E. More specifically, the ventilation box 150 is arranged at the top of the dihedral forming the gutter 120 (that is to say the base of the V). The ventilation box is therefore located upstream of the fuel supply rail 140. Such a ventilation box 150 has the function of cooling the walls of the gutter 6, as well as cooling the rail 140 for fuel injection. In this respect, the ventilation box 150 is supplied with cooling air from the secondary flow F2 and comprises a plurality of ventilation orifices 152 through which the cooling air is projected into the enclosure E, against the elements to be cooled. .

The cooling of the fuel injection rail 140 is useful even in the absence of afterburner, because it prevents fuel residues from entering a coking process.

The flame holder arm 120 also includes a protective screen 160 (or heat screen), which extends along the longitudinal direction B inside the gutter 122, in the enclosure E. More precisely, the screen of protection 160 is disposed downstream of the fuel injection rail 140. Except at its ends, the protection screen 160 has a V-section with two wings 162a, 162b which diverge downstream to form, with the wings 122a, 122b of the gutter 122, a sprayed fuel ejection channel. In other words, to define the enclosure E, except at its radial ends, the protective screen 160 has substantially (except for curvatures in particular, and in particular the base where the shape is generally rounded) an open dihedral shape with the two wings 162a, 162b and whose intersection line extends in the longitudinal direction B.

The function of the protective screen 160 is to protect the fuel injection rail 140, the ventilation box 150 and the gutter 120 against the flames hanging on the trailing edges of the wings 122a, 122b of the gutter 120. For this , the protective screen 160 can be made of CMC.

The fuel, shown schematically by dotted arrows in FIG. 6 , is propelled against the wings of the gutter 122a, 122b and is evacuated between these wings 122a, 122b and the protective screen 160, in order to participate in the combustion.

The protective screen 160 can include holes for fixing and centering, for maintaining it on the gutter 122 and aligning it with the ventilation box 150.

The protective screen 160 is therefore positioned in the enclosure E and separates it into two spaces: a confined space Ec, where the ventilation box 150 and the fuel injection rail 140 are located, and an open space Eo , open to the outside, i.e. to the vein V.

Preferably, the ends of the wings 162a, 162b of the protective screen 160 are substantially at the same level as the ends of the wings 122a, 122b of the gutter 120.

In order to ignite the air-fuel mixture, the afterburner 100 comprises a spark plug 170. The spark plug 170 comprises a body 171 and electrodes 172 capable of generating a spark which makes it possible to ignite the air-fuel mixture. The body 171 represents the major part of the volume of the spark plug 170 and houses all the components necessary for the generation of the spark by the electrodes 172.

The candle 170 is positioned, at least partially, in the enclosure E. In particular, the electrodes 172 are positioned in the enclosure E. This means that the rest of the candle 170 may not be positioned in the enclosure E, as shown in Figures 4 and 5 .

Ignition therefore takes place in the primary flow F1, in a hotter environment than in the secondary flow F2, which increases the ignition range and the ignition probabilities in this range.

More precisely, the electrodes 172 are positioned in the open space Eo of the enclosure E, that is to say on the open side of the protective screen 160. The protective screen 160 (and therefore the gutter 120 ) therefore surrounds candle 170 over more than 180°.

The spark plug 170 extends up to between 1% and 20% of the length of the flame holder arm 120 in the longitudinal direction B, from the radially outer end, that is to say of the afterburner casing 110. More specifically, a length between 10% and 15% is suitable.

In Figures 4 and 5 , two different inclinations of candles 170 are illustrated. These two variants involve different adaptations of the flame holder ring 130 and in particular the adaptation of the wings of the flame holder ring 130.

In fact, passage orifices or a localized indentation are provided in the wings of the combustion ring 130 to allow the insertion of the spark plug 170 so that the electrodes 172 are located in the enclosure E. Typically, given the inclination parallel or almost parallel to the radial direction of the spark plug 170 and given the presence of the enclosure E radially inside the flame holder ring 130, two through holes are necessary in the variant of Figure 4 , and two notches are suitable in the variant of Figure 5 ,. In the case of openings, sliding crossings can be put in place.

The protective screen 160 further comprises a plurality of free orifices 164 allowing the fuel to pass from the confined space Ec to the open space Eo (where the spark plug 170 is located) by crossing the protective screen 160 .

The free orifices 164 are therefore located longitudinally where the spark plug 170 is located (more precisely the electrodes of the spark plug 170) but they can be provided over the entire length or a major part of the length of the protective screen 160.

Due to the shape of the protective screen 160, the free orifices 164 are oriented towards the same point or the same zone, which is that where the spark plug 170 is located.

Apart from the integration of the spark plug 170, the rest of the postcombustion device 100 remains unchanged: the ventilation box 150 and the fuel injection rail 140 do not need to be modified or adapted, which ensures a simple implementation, in particular on existing turbojet engines.

Claims (10)

Afterburner device (100) for a turbojet engine, configured to extend at least partially within a gas stream (V) of a turbojet engine, the afterburner device (100) comprising:
- a flame holder arm (120) comprising a gutter (122) extending in a longitudinal direction (B) defining an enclosure (E) open downstream, the gutter (122) being configured to form an obstacle in the primary gas stream flow (F1),
- a candle (170),
the device being characterized in that the candle (170) is positioned at least partially in the enclosure (E). Afterburner according to claim 1, wherein the plug (170) comprises electrodes (172), said electrodes (172) being positioned in the enclosure (E). Postcombustion device (100) according to any one of claims 1 to 2, in which the flame holder arm (120) further comprises a protective screen (160) extending in the longitudinal direction (B) and separating the enclosure (E) into a confined space (Ec) and an open space (Eo), in which the plug (170) is positioned at least partially in the open space (Eo). Afterburner (100) according to Claim 3, in which the protective screen (160) comprises a plurality of free orifices (164), to allow the air-fuel mixture to escape from the confined space (Ec ) to the open space (Eo). Postcombustion device (100) according to any one of claims 1 to 4, in which the gutter (122) has a V-shaped section, open on the downstream side. Afterburner device (100) according to any one of Claims 1 to 5, in which the flame holder arm (120) further comprises a fuel injection rail (130) extending in the longitudinal direction (B) in the enclosure (E), Afterburner (100) according to any one of claims 1 to 6, wherein the fuel injection rail (140) extends in the longitudinal direction (B) in a diffusion length longer than half of the length of the gutter (122) and includes a plurality of diffusion ports (142) for supplying fuel to the flame tamer arm (120) along the diffusion length. An afterburner (100) according to any of claims 1 to 7, wherein the spark plug (170) extends a spark plug length of between 5 and 20% of the length of the flame holder arm (120). An afterburner (100) according to any of claims 1 to 8, further comprising a flame holder ring (130), located at one end of the flame holder arm (120), the afterburner ring (130) comprising two wings, the two wings comprising passage openings and/or notches to allow the passage of a body (171) of the spark plug (170). A turbojet engine comprising an afterburner device (100) according to any one of the preceding claims.