EP1840469B1 - Afterburner flame-holder arm - Google Patents

Description

The present invention relates to a flame-holder arm of an afterburner chamber in a turbomachine such as a turbojet engine.

Conventionally, an afterburner comprises a series of flame-holder arms which are each formed of a hollow dihedron whose crown edge is oriented upstream of the chamber and which is closed on the downstream side by a thermal protection screen. A fuel rail extends radially inside the arm from an outer casing of the chamber. This ramp is connected to fuel supply means and has fuel spray holes (see for example the documents EP-A-1619441 and FR-A-2,709,342 ).

A ventilation box extends in the arm substantially parallel to the ramp, between the latter and the edge of the dihedral arm, and has at its radially outer end a cooling air intake opening for distribution in the arm through holes in the box. The radially inner end of the ventilation box is closed and comprises a centering finger engaged in an orifice of the arm.

The ventilation box also comprises, in the vicinity of its radially inner end, a lug protruding downstream and whose free end is engaged in a corresponding orifice of the thermal protection screen to maintain the ventilation box . An orifice formed in the lug receives the lower end of the fuel rail to center it in the arm.

During assembly, the arm is assembled with the ventilation box and the thermal protection screen which is fixed on the arm by means of welded and welded pins and which immobilizes the ventilation box. Then, the fuel rail is mounted in the arm from the outer casing of the chamber, by engagement of its radially inner end between the thermal protection screen and the ventilation box, until this end is housed in the centering hole formed in the lug of the box.

However, this operation is performed blind, which may lead to improper assembly of the ramp whose inner end can engage in a free space between the lug and a side wall of the arm. This results in a poor distribution of the sprayed fuel in the arm and a degradation of the cooling of the arm, resulting in a possible destruction of the thermal protection screen.

In operation, the ventilation box is subjected to significant vibrations that cause frictional wear of its lug and the corresponding orifice of the thermal protection screen, which results in a displacement of the box inwards, and by exceeding the box finger in the primary flow, and wear and enlargement of the orifice of the arm which receives the centering pin of the box.

Moving the vent box inward may cause the fuel rail to disengage from the pin hole and rupture the boom.

To improve the situation, in particular EP1593911 or EP1619441 propose solutions. EP1619441 discloses a flame holder arm with the features of the preamble of claim 1 and a vent box with the features of the preamble of claim 7.

Thus disclosed is the use of a post-combustion chamber flame-holder arm, said arm comprising an open dihedral-shaped body, a ventilation box extending inside the body and having at one end a centering finger engaged in an orifice of the body, a fuel rail extending inside the body along the ventilation box, means for guiding and centering the ramp relative to the box, and a protective screen thermal device fixed on the body and closing the open face of the dihedron, the ventilation box comprising immobilization means in the body of the arm which are independent of the thermal protection screen.

Thus, the centering and immobilization of the ventilation box in the flame holder arm are assured independently of the screen of thermal protection, which eliminates the centering pin and fixing provided on the box in the prior art.

But, the blind assembly of the fuel rail in the body of the arm can still result in an improper layout of the ramp and cause wear and degradation of the fuel rail and the body of the arm.

In order to provide a simple, effective and economical solution to all of these problems, the invention proposes that the flame-holder arm of an afterburner chamber, thus comprising, as mentioned above, a dihedral shaped body. open, a ventilation box extending inside the body and having at one end a centering finger engaged in an orifice of the body, a fuel rail extending inside the body along the ventilation box , guiding and centering means of the ramp relative to the box, and a thermal protection screen attached to the body and closing the open face of the dihedron, the ventilation box comprising immobilization means in the body of the arm, which are independent of the heat shield, or such that the centering finger comprises an annular shoulder intended to bear on the edge of the orifice of the body of the arm, inside the arm, that the end on point external to the arm comprises means for retaining the finger in the orifice, that the retaining means comprise an annular piece fixed by brazing or welding on the finger of the box, and that the annular shoulder of the box finger is applied to the arm by the annular piece fixed at the end of this finger.

This ensures a setting without play of the box on the body of the arm and avoids the radial vibrations of the box relative to the body of the arm.

It can also be expected that this annular piece comprises at least one flat cooperating abutting with a corresponding element of the body of the arm to participate in the immobilization in rotation of the box relative to the arm.

• l'usure de l'écran de protection thermique qui résultait des vibrations de cet ergot dans l'orifice de réception formé dans l'écran,
• l'usure du doigt de centrage dans l'orifice formé dans le corps du bras et l'usure correspondante des bords de cet orifice,
• les risques de rupture de la rampe de carburant par désengagement des moyens de centrage et de guidage formés sur le caisson de ventilation.

The presence of the transverse flange inside the arm body prevents mounting the end of the fuel rail other than the centering hole formed in this flange.
It should be noted that, thanks to the global solution above, we have deleted:

• the wear of the thermal protection screen resulting from the vibrations of this pin in the receiving orifice formed in the screen,
• the wear of the centering finger in the orifice formed in the body of the arm and the corresponding wear of the edges of this orifice,
• the risk of rupture of the fuel rail by disengagement of the centering and guiding means formed on the ventilation box.

Preferably, the centering pin of the box passes through the orifice formed in the body of the arm and comprises said means for immobilizing the box on the body of the arm.

The invention also proposes a ventilation box for a flame holder arm, comprising an open end and an end formed with a substantially axial finger, characterized in that this finger has an annular support shoulder on a support.

This ventilation box is further characterized in that it is formed with a transverse flange having a through hole whose axis is substantially parallel to the longitudinal axis of the box.

The invention also relates to a turbomachine, such as an airplane turbojet engine with an afterburner chamber, characterized in that it comprises at least one flame holder arm of the type described in the foregoing.

• la figure 1 est une vue schématique partielle en coupe axiale d'une chambre de post-combustion d'une turbomachine ;
• la figure 2 est une vue à plus grande échelle d'une partie d'un bras accroche-flammes de la figure 1 et illustre un dispositif de fixation d'un caisson de ventilation dans le bras accroche-flammes selon la technique antérieure ;
• la figure 3 est une vue en coupe selon la ligne III-III de la figure 2, à plus grande échelle ;
• la figure 4 est une vue correspondant à la figure 2 mais illustre un dispositif de fixation selon l'invention ;
• la figure 5 est une vue en coupe selon la ligne V-V de la figure 4, à plus grande échelle.
• la figure 6 est une vue de dessous du bras de la figure 4.

The invention will be better understood and other details, characteristics and advantages of the present invention will appear on reading the following description given by way of nonlimiting example and with reference to the appended drawings in which:

• the figure 1 is a partial schematic view in axial section of an afterburner chamber of a turbomachine;
• the figure 2 is a larger-scale view of a part of a flame-holder arm of the figure 1 and illustrates a device for fixing a ventilation box in the flame-holder arm according to the prior art;
• the figure 3 is a sectional view along line III-III of the figure 2 , see you large scale ;
• the figure 4 is a view corresponding to the figure 2 but illustrates a fixing device according to the invention;
• the figure 5 is a sectional view along line VV of the figure 4 , on a larger scale.
• the figure 6 is a bottom view of the arm of the figure 4 .

We first refer to Figures 1 to 3 wherein a flame holder arm 10 of the prior art is mounted on a casing 12 of an afterburner chamber of a turbojet engine at its radially outer end, said arm 10 extending substantially radially in the chamber post-combustion and passing through a confluence sheet 14 which separates the primary stream 16 of the hot combustion gases from the secondary stream 18 provided by a fan mounted at the front of the turbojet engine.

In known manner, the flame holder arm 10 comprises a body 20 in the form of an open dihedron, whose apex edge 22 is oriented upstream and whose opening is turned downstream and in which are arranged a ventilation box 24, a fuel rail 26 and a thermal protection screen 28 having a section C and which closes the open face of the body 22.

The ventilation box 24 extends inside the arm along the crown edge 22 and comprises a radially outer end which is open and is supplied with air from the secondary flow 18 through an opening in the radially outer portion of the body of the arm. The radially inner portion of the box 24 comprises multiple perforations of air distribution inside the arm.

The radially inner end of the casing forms a cylindrical finger 30 which is engaged without play in an orifice of the base 32 of the body of the arm, the end of the finger 30 coming flush with the outer face of this base 32 without protruding from the outside the arm.

In the vicinity of this radially outer end, the housing of ventilation 24 comprises a tab 34 which extends downstream in the direction of the heat shield 28, substantially perpendicular to the longitudinal axis of the box 24, and whose free end forms a lug 36 engaged in a corresponding orifice of the screen 28.

This tab 34 also comprises, in an intermediate portion between the ventilation box 24 and the lug 36, a through hole for receiving the lower part of the fuel rail 26 for centering this ramp inside the arm 10 .

On assembly, the ventilation box 24 is first disposed in the body 20 of the arm 10, then the thermal protection screen 28 is put in place, the lug 36 of the ventilation box being engaged in the opening of the housing. screen, then the screen 28 is fixed by welding at four points 34 on the side walls of the body 20 of the arm, thus fixing the ventilation box 24 inside the arm. The fuel rail 26 is then blindly mounted inside the arm from the radially outer end thereof. This operation requires particular care because the lower end of the fuel rail 26 must be engaged in the hole provided in the lug 34 of the ventilation box 24 and not between this lug 34 and a side wall of the body 20 of the arm 10.

In operation, the ventilation box 24 is subjected to radial vibrations inside the arm 10, which results in wear of its lug 36 and the edges of the corresponding orifice of the heat shield 28 as well as by a wear of the finger 30 of its radially inner end and the edges of the corresponding orifice formed in the base 32 of the arm 10.

These wears result in a descent of the box 24 inside the arm 10, the end of the finger 30 projecting under the base 32 of the arm 10 and disturbing the conditions of the afterburner. In addition, this displacement of the ventilation box 24 in the arm 10 may allow the radially inner end of the fuel rail 26 to disengage from its guide orifice formed in the lug 34 of the housing. ventilation, which causes the rupture of the fuel rail 26.

To avoid these drawbacks, the invention proposes that the ventilation box 24 be mounted and fixed inside the arm 10 independently of the thermal protection screen 28, as has been shown in FIGS. Figures 4 to 6 .

In these figures, the radially inner end of the ventilation box 24 comprises a cylindrical finger 40 which extends in the axis of the box 24 and which has an annular shoulder 42 forming a bearing surface on the edge of the orifice 44 formed in the base 32 of the arm 10, the cylindrical finger 40 extending outside this orifice and carrying an annular piece 46, such as a washer for example, which is fixed, for example by welding or brazing, on the end of the finger 40.

Advantageously, the orifice 44 is formed in the bottom wall 48 of a small recess 49 of the base 32 of the arm 10, this bottom wall 48 being perpendicular to the axis of the box 24 and the finger 40.

When this recess 48 is not cylindrical in shape, as shown schematically in figure 6 the annular piece 46 can be given a corresponding shape so that this annular piece has a function of anti-rotation of the finger 40 and therefore of the box 24 around their longitudinal axis.

One or two flats may also be formed in the contour of the annular piece 46, this flats or flats corresponding to planar faces of the recess 48 to give this anti-rotation function to the annular piece 46.

As can be seen from the Figures 4 and 5 , the ventilation box 24 no longer includes the lug 36 engaged in an orifice of the heat shield 28 and the lug 34 shown in FIG. figure 1 is replaced by a transverse rim 50 of the box 24, this flange 50 being in the form of an angular sector and extending inside the body 20 of the arm 10 so as to occupy, in a transverse plane, the major part of the space available inside the arm 10 between the box 24 and the screen of thermal protection 28.

In the example shown, the sides 52 and 54 of the flange 50 are approximately parallel to the side walls of the arm 10 and the screen 28 respectively, and extend a short distance from these walls, prohibiting a mounting of the radially internal end of the fuel rail 26 other than in the guide hole 56 formed in the flange 50. It thus greatly facilitates the blind assembly of the fuel rail 26 in the arm 10 and avoids any incorrect arrangement of the fuel rail, ensuring better cooling of the arm 10 by the fuel and extending the service life of the arm.

The axial fixing without play of the end finger 40 of the box 24 in the hole 44 of the base 32 of the arm 10 avoids the radial vibrations of the ventilation box 24 in the arm and the resulting wear of the arm and the box.

In case of burning of the thermal protection screen 28, the ventilation box 24 remains in the arm 10 and continues to perform its function of cooling the various elements of the arm. The fuel rail 26 is also held in place on the ventilation box 24 inside the arm and can not break.

Claims (9)

1. Flameholder arm for an afterburner comprising a body (20) in the form of an open dihedron, a ventilation duct (24) extending inside the body and comprising, at one end, a centering finger (40) engaged in an orifice (44) in the body, a fuel injection harness (26) extending inside the body along the ventilation duct (24), means for guiding and centering the harness (26) with respect to the duct (24) and a heatshield (28) fixed to the body (20) and closing the open face of the dihedron, the ventilation duct (24) comprising means (46) of immobilization in the body of the arm which are independent of the heatshield, said arm being characterized in that the centering finger (40) comprises an annular shoulder (42) intended to come to bear against the edge of the orifice (44) in the body of the arm, on the inside of the arm, in that the end of the finger (40) external to the arm comprises means (46) for retaining the finger in the orifice, in that the retaining means comprise an annular component (46) fixed by brazing or welding to the finger of the duct, and in that the annular shoulder (42) of the finger of the duct is pressed against the arm by the annular component (46) fixed to the end of this finger.
2. Arm according to claim 1, characterized in that the ventilation duct centering finger (40) passes through the orifice (44) of the body and comprises means (46) for immobilizing the duct on the body of the arm.
3. Arm according to claim 1 or 2, characterized in that the annular component (46) comprises at least one flat collaborating, by butting against it with a corresponding element of the arm in order to prevent the finger from rotating in the orifice.
4. Arm according to one of the preceding claims, characterized in that the ventilation duct (24) comprises a transverse lip (50) comprising an orifice (56) for centering the fuel injection harness (26).
5. Arm according to claim 4, characterized in that the transverse lip (50) of the duct occupies almost all of the available space inside the arm (10) so as to prevent the fuel injection harness (26) from being fitted incorrectly.
6. Arm according to claim 4 or 5, characterized in that the ventilation duct (24) is formed as a single piece with the finger (40) and the transverse lip (50).
7. Ventilation duct of a flameholder arm, comprising an open end and an opposite end formed with a substantially axial finger (40), characterized in that this finger has an annular shoulder (42) for bearing against a support.
8. Ventilation duct according to claim 7, characterized in that it is formed with a transverse lip (50) comprising a through-orifice (56) the axis of which is substantially parallel to the axis of the duct.
9. Turbo machine with after burner, characterized in that it comprises at least one flameholder (10) arm according to claims 1 to 6.

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