Combustion chamber floor of a turbine engine

Description

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to the field of combustion chambers for aircraft gas turbomachines.

[0002] In the field, such combustion chambers are known, comprising: two internal and external walls respectively (also called internal and external shells, or longitudinal walls), and a chamber bottom (FDC) extending between said internal and external walls and comprising first openings for mounting devices for injecting (in particular) combustion air to inject this combustion through said openings.

[0003] A deflector is also often arranged downstream of the bottom wall, to protect it thermally from the hearth of the combustion chamber in which combustion takes place, the deflector having second openings for mounting said oxidant injection devices (i.e. configured for this purpose), the first and second openings then being a priori coaxial. For the record, the hearth of a combustion chamber is delimited by said longitudinal walls and the chamber bottom.

[0004] This is the case in EP 1 785 671.

[0005] Typically, two main functions of a baffle are to thermally protect the chamber bottom, which is often more structural, and to create a "cup" film for upstream cooling of the (inward-facing surfaces of the chamber) internal and external walls, thanks to the impact flow coming from the pierced chamber bottom. However, it turns out that this flow in the primary zone of the hearth (upstream part) disturbs the stability of the combustion and the early cooling of the internal and / or external walls accentuates the thermal gradient in the critical zone, around holes passing through them, typically called primary and / or dilution holes.

[0006] For combustion in the combustion chamber, fuel injection devices for injecting fuel through at least said first openings are also provided on these combustion chambers.

[0007] In this application: axial has the meaning: extending (substantially) parallel to the general axis of the combustion air supply (or injection) system and the fuel injector heads, which general axis is also that of the aforementioned first mounting openings; internal and external has the meaning (substantially) radially internal and radially external with respect to: -- the longitudinal axis X around which the combustion chamber extends, for the aforementioned longitudinal walls of the chamber, or -- said aforementioned general axis (axis 122a below), for the other elements referred to in this text; the expressions upstream and downstream are to be considered with reference to the general direction of circulation of the air in the combustion chamber, the air concerned here arriving from upstream (of the compressor(s)) to, with fuel, enter the combustion chamber through the bottom of the chamber, the gases resulting from the combustion exiting downstream to then pass into the turbine(s).

[0008] FR 2 998 038 discloses a combustion chamber in which there is a chamber bottom with two walls: upstream and downstream, the second acting as a deflector, with a space (or an enclosure) between them, this space being supplied with air via multi-perforations, in order to ensure cooling by impact of the downstream wall, which is directly exposed to the radiation of the flame. The air is then ejected through slots or holes towards the (said surfaces facing the interior of the chamber of the) internal and external walls in order to initiate a film of air which is then relayed by the multi-perforation holes of these walls. EP 1 785 671 A1 also discloses another combustion chamber.

[0009] In the present patent, the chamber bottoms of such combustion chambers are in particular concerned.

[0010] A technical issue addressed here concerns the deterioration of the in-service condition of the chamber bottom. Burning phenomena have been observed at the chamber bottom. Cracks have also been observed.

[0011] Based on the analyses carried out, the thermal level of exposure of these various parts appears to be the cause of the damage observed. Indeed, the area concerned is massive and has high thermal inertia. However, current technology makes it difficult to cool.

[0012] It is in order to provide a solution to at least some of the difficulties mentioned above that it is proposed to develop a combustion chamber for a gas turbomachine for aircraft comprising: longitudinal walls extending parallel to an axis (122a below), a hearth where combustion takes place, at least one bottom wall connected to said longitudinal walls and extending transversely to them, the bottom wall comprising: -- at least one axial opening, -- holes passing through it, for the passage of cooling air between at least one inlet orifice and at least one outlet orifice of said holes, the holes extending along the bottom wall inside the latter, the outlet orifice being located closer to said at least one opening than the inlet orifice, and -- at the outer periphery, a curved part forming a rim, and at least one combustion air supply system comprising a bowl mounted in said at least one opening, or in one piece with said at least one bottom wall, with the important characteristic that at the location of said rim the bottom wall is fixed with the longitudinal walls.

[0013] By fixing the chamber back wall (with its air passage holes along it) and the longitudinal walls (internal and external walls mentioned above) together by this edge, an indirect thermal impact on these longitudinal walls is expected. The fixing can be carried out by means of screws.

[0014] The expression "along the chamber bottom wall" indicates that said holes extend (at least over the majority of their length) transversely to the thickness of this wall, internally. Considering a substantially flat area of ​​this bottom wall, said holes extend, inside this wall, substantially in the plane thereof, and therefore not transversely to this plane. Since the chamber bottom extends (generally) between said internal and external walls, said internal holes will extend (at least over the majority of their length) substantially transversely to the aforementioned longitudinal axis of the combustion chamber

[0015] Furthermore, these holes will favorably define (air) ducts. The expression "duct" is intended to indicate that said holes will favorably be very long in relation to their cross-section(s), typically their diameter(s), this ratio thus being greater than 5, or even preferably 10, including if said cross-section varies. The maximum cross-section will then be considered.

[0016] Each of these holes will thus be able to ensure a circulation of cooling air supplied by the highest available pressure differential. The air flow obtained will allow calories to be recovered by pumping into the bottom of the chamber. It will also be possible to at least limit the use of a deflector (see below).

[0017] According to the invention, the inlet orifice of the hole(s) in question will be located towards an external periphery of the chamber bottom wall.

[0018] This will allow for easier construction (access via this periphery) and the potential longest length of holes or pipes, with therefore an optimized thermal effect.

[0019] According to the invention, the combustion chamber: which is adapted so that air circulates there, from upstream (AM) to downstream (AV; arrow 111 figure 2 ), passing successively: -- in said at least one axial opening and said holes in the bottom wall, then, -- in the hearth, will be such that said rim is oriented upstream, said at least one inlet orifice being preferably located towards a free end of the rim (therefore possibly at a certain distance from the free end of the rim).

[0020] In addition to the above advantages, this edge can then be used to both fix the aforementioned walls and manage the aforementioned thermal problem in an optimized way (by extending the length of the said holes).

[0021] According to the invention, the rim is oriented upstream. This also makes it easier to let in air, which will also be cooler.

[0022] According to the invention, said holes will open onto the edge of the chamber bottom wall at the location of the inlet orifices. Preferably, said holes will open onto the edge of the bottom wall at the location of the outlet orifices.

[0023] We will then favor all the more, respectively, an easier realization and a significant length of holes. In addition, opening the outlet orifices of the holes on the edge (radially internal) of the chamber bottom wall, or at least in the immediate environment of said (each) mounting opening of the combustion air supply system(s), will allow the air flow obtained, having recovered calories by pumping in the chamber bottom, to open into the chamber (inlet of the hearth) to feed the combustion. Note that such heated air will be beneficial for the stability of the combustion, the pipes (holes) being fed by the highest available pressure differential.

[0024] At least some of said holes may individually define a sinuous line over at least part of their length.

[0025] Thus, we can move towards making the holes / pipes as precisely as possible so that the chamber back wall provides both a structural function and is effectively cooled. Thus, a sinuous shape will allow us to maintain a constant material thickness (at least sufficient) and maximize the exchange surface so as not to create mechanical weakness or an area likely to promote hot spots. It will help to take into account the issues of homogenizing the thermal performance of the chamber back and its lifespan.

[0026] Also concerned is a combustion chamber of a gas turbomachine for aircraft, in itself, comprising: of said longitudinal walls, a said hearth where combustion takes place, at least one said chamber bottom wall, with all or part of the aforementioned characteristics, connecting these longitudinal walls, and at least one said combustion air supply system (SI) comprising a bowl mounted in said at least one opening, or in one piece with said at least one chamber bottom wall which is provided with it.

[0027] Preferably, the combustion air supply system(s) will further comprise at least one supply passage towards an external periphery of the bowl, and / or at least one spiral, provided respectively to be supplied with combustion air to be supplied inside the bowl, mixed with the air having passed through said second holes.

[0028] Thus, in particular with outlet orifices of the aforementioned air holes opening onto the (radially internal) edge of the chamber bottom wall, or at least in the immediate environment of said (each) mounting opening of the combustion air supply system(s), it will be possible, in addition to recovering calories by pumping into the chamber bottom, to feed the combustion with this heated air, thus favouring the stability of the combustion.

[0029] In connection with the above, it is proposed that the aforementioned bowl is (typically at the location of a flared part) crossed by second holes and / or third holes for the passage of fluid (a priori only air). These second holes and / or third holes will open into the hearth of the combustion chamber and, close to them, will be able to open at least some of the outlet orifices (of at least some) of said holes in the chamber bottom wall, so that (heated) air having passed through these holes can also pass through said second and / or third holes, therefore towards said hearth.

[0030] In connection with the aforementioned aspect concerning the combined effect of fixing said chamber bottom wall and thermal management in the environment of this fixing, it is proposed that at the location of a said rim formed, at the external periphery of the wall, by a curved part, said at least one chamber bottom wall is fixed with the longitudinal walls by screws which will bypass certain of said holes / channels of the chamber bottom wall.

[0031] With a combustion chamber having all or part of the aforementioned characteristics, it will thus be possible to have a chamber back wall which directly faces the interior hearth of the chamber, without the interposition of a deflector plate, understood to be arranged opposite, slightly downstream of said back wall, as it is transverse to said internal and external walls.

[0032] In fact, with a chamber bottom wall without a transverse hole (i.e. substantially axial) for the cooling air (holes previously called "multi-perforations"), it will be possible to produce such a wall and a deflector in a single piece. The cup film function could then be eliminated and the thermal and structural functions could be provided by the single-piece chamber bottom. The weight saving compared to separate parts would depend on the cooling requirement and the mechanical strength.

[0033] It is thus further proposed that the manufacture of said chamber bottom wall be carried out by additive manufacturing, by providing for the manufacture of said holes in this wall with a section smaller than the remaining thickness of said bottom wall on either side of this section.

[0034] It will then become possible to integrate a network of holes forming pipes into a relatively small space, with therefore, expected weight savings and efficient and optimized cooling of critical areas. Additive manufacturing must make it possible to construct said holes / pipes as precisely as possible to ensure both the structural function and the cooling function of the chamber bottom. Thus, possible sinuous shapes as mentioned above will make it possible to maintain a constant material thickness and maximize the exchange surface so as not to create mechanical weakness or an area likely to promote hot spots.

[0035] The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of non-limiting example with reference to the appended drawings. BRIEF DESCRIPTION OF THE FIGURES

[0036] there figure 1 is a diagram of a combustion chamber of a gas turbomachine according to the prior art; the figure 2 is a section along the II-II direction of the figure 3 of an upstream part of a gas turbomachine combustion chamber, with a bottom wall in accordance with the invention; the figure 3 is a diagram of a sector of this bottom wall fixed with said internal and external walls of said chamber; the figure 4 is an enlarged diagram of said sector of this back wall; the figure 5 shows a bypass of a fixing screw; the figures 6,7 schematize the shapes of said holes or air ducts passing through the back wall of the chamber, the figure 7 also presenting a local enlargement; the figure 8 is a sinuous-shaped diagram of said holes or air ducts; and the figures 9,10 , 11 outline alternatives to the method of realizing the figure 2 . DETAILED DESCRIPTION

[0037] There figure 1 illustrates a combustion chamber 10 of a gas turbomachine 1 for an aircraft in accordance with the prior art. The turbomachine 1 comprises, upstream (AM) relative to the overall direction of circulation of the gases in the turbomachine (arrow 11) a compressor not shown in which air is compressed before being injected by an annular diffusion duct into an external chamber casing 5, then into the combustion chamber 10 mounted in this external casing 5. The compressed air is introduced into the combustion chamber 10 and mixed with fuel from injectors 12. The gases resulting from the combustion are directed towards a high-pressure turbine not shown, located downstream (AV) of the outlet of the chamber 10. The combustion chamber 10, which is of the annular type, comprises a radially internal wall 14 and a radially external wall 16 (also called longitudinal walls), the upstream ends of which are connected by a bottom wall 18 extending substantially radially.The bottom wall 18 comprises a plurality of axial openings 19 used for mounting combustion air injection devices 20 also called combustion air supply systems. Fuel injector heads 12 are also engaged opposite the openings 19. Holes, for circulation of dilution and / or cooling air, 140 and 160, can pass through the internal 14 and / or external 16 walls, respectively.

[0038] The longitudinal walls 14 and 16 may be substantially coaxial with each other and parallel to the axis 22a, this axis belonging to the section plane of the figures 1 , 2 And 9-11and therefore being the general axis of alignment of each combustion air injection device 20 and of each associated fuel injector head 12. The combustion chamber 10 develops, on the other hand, annularly, around the axis X which is the general axis of the turbomachine 1 around which the rotating elements of the compressor(s) and the turbine(s) rotate. In the example, an acute angle exists between the axes X and 22a. These two axes could be parallel. The chamber bottom 18 of the combustion chamber 10 further comprises deflectors 24 mounted downstream of the bottom wall 18 and intended to protect it from the flame formed in the hearth 15 of the combustion chamber 10, defined between the walls 14, 16. The deflectors 24 are arranged, in successive sectors around the axis X, adjacently by their lateral edges, so as to form an annular ring of deflectors.

[0039] The bottom wall 18 has multiple perforations 28 serving for the passage of air from the compressor and opening into the annular space 30 formed between the bottom wall 18 and the deflectors 24. The ventilation of the bottom wall 18 may not be uniform over its entire circumference.

[0040] On the figures 2-11 , which illustrate several embodiments of the invention, respectively monobloc and non-monobloc, with different drillings, the parts identical, and / or with identical functions, to those presented in relation to the figure 1 have the same benchmark, increased by 100.

[0041] Thus we see that, in all the embodiments detailed below, we find, as in the figures 2-11 , an annular wall 118 at the bottom of the annular combustion chamber connecting together, by means of fasteners (such as the screws 32), the longitudinal walls 114, 116, substantially transversely to them. The bottom wall 118 has: openings 119 for mounting the combustion air supply systems 120, and holes 128 passing through it, for the passage of cooling air, between at least one inlet orifice 128a and at least one outlet orifice 128b of these holes.

[0042] Furthermore, in order to seek to overcome at least some of the problems and drawbacks mentioned above, it is proposed in the invention that, as already explained, the holes 128 for the passage of cooling air passing through the bottom wall 118 extend internally along this bottom wall, between at least one said inlet orifice 128a and at least one said outlet orifice 128b.

[0043] Compared to the opening 119 which is most adjacent to it, the outlet orifice 128b is located closer to the opening 119 than the inlet orifice 128a, as can be seen better. figure 4 .

[0044] Thus, it is in (internally along) the total thickness e of the bottom wall 118 that at least part of these cooling air passage holes 128 will pass, or circulate.

[0045] To achieve this, it will certainly be favorable in practice to locate the (each) inlet orifice 128a towards an external periphery 178a (external with respect to the axis 122a) of said bottom wall 118.

[0046] Rather than being a single block over 360°, the bottom wall 118 will preferably comprise, around the axis 122a, a circumferential succession of wall sectors 148a each provided with an opening 119; see in particular figure 3 .

[0047] For its fixing, the bottom wall 118 has, at its external periphery, an annular rim 138a for fixing to the upstream end of the external wall 116 of the chamber, and, at its internal periphery, an annular rim 138b for fixing to the upstream end of the internal wall 114 of the chamber. It will be a priori preferred that the external annular rims 138a and 138b internal are turned upstream. They may be substantially cylindrical. The fixing itself is, in the preferred example, ensured by means of the screw-nut type 32 which pass through orifices 34 formed in the rims 138a, 138b, radially to the axis 122a; see figure 5 .

[0048] To combine fixing and cooling qualities, it is proposed that some of said holes 128 of the bottom wall bypass the screws 32 (and their orifices 34); figure 5 .

[0049] It is in particular towards the respective upstream free ends 158a, 158b of these fixing edges 138a, 138b that the inlet orifices 128a of the aforementioned cooling air passage holes 128 will be located; see figures 5 , 6 .

[0050] Thus, it is then away from the hot and fixing zones, from the free edge 168a and / or 168b of these fixing edges 138a, 138b, that the cooling air can circulate in the wall 118.

[0051] Towards the exit, after having conducted the air, the holes 128 can also open onto the inner edge 168c of the bottom wall; see figures 3 , 9 .

[0052] In this way, the bottom wall 118 can be cooled as best as possible, sector by sector, if it is thus formed.

[0053] In the thickness of the bottom wall 118, the section of the holes 128 may be constant or variable. It may be rectangular ( figure 6 ) or circular ( figure 7 ), For example.

[0054] On this point, we can see on most of the figures 2 and following that the holes 128 are, as preferred, very long compared to their cross-section (whether this is unique or variable), this ratio being greater than 5, or even preferably 10, including if said cross-section varies. The maximum cross-section will then be considered. The expression "pipeline" aims to mark this length (L) / section (S) ratio > 5, as can be seen for example figure 5 .

[0055] The number of inlets 128a and the number of outlets 128b will be defined according to requirements. An inlet will not necessarily correspond to a single outlet; and vice versa. For example, a single inlet 128a in the form of a long slot can be provided, with internal connections 36 at the bottom of the chamber ( figure 7 ) or outlets at different locations; for example, an outlet at the air injection system (bowl holes and collar) and an outlet along the wall 118.

[0056] In particular by additive manufacturing (one of the manufacturing processes, most of the time computer-assisted, aiming at shaping a part by adding material, by stacking successive layers), it will be possible to manufacture / construct holes / pipes 128 to ensure as accurately as possible both the structural function and the cooling function of the bottom 118 of the chamber. It will thus be possible for at least some of these holes or pipes to individually define a sinuous line, over at least part of their length, as on the figure 8 , thus allowing a constant material thickness to be maintained and the exchange surface to be maximized so as not to create any mechanical weakness or area likely to promote hot spots.

[0057] With additive manufacturing, it will be possible in particular to manufacture the holes / pipes 128 of the wall 118 with a section e1 (such as a diameter) less than the remaining thickness (e2a + e2b) of said bottom wall, on either side of this section; i.e. e1 < e2a + e2b; figure 7 This will allow: to assemble a chamber bottom and a deflector in a single part, and that the holes / pipes 128 are supplied by the highest available pressure differential, and to produce holes / pipes 128 of very small diameter, over a travel distance in the part of several cm, and for trajectories which are possibly not straight.

[0058] Diameters e1 of holes / pipes 128 less than a millimeter must allow a low thickness (e2a+e2b) of the chamber bottom to be maintained and a guaranteed structural role. A minimum thickness of material will thus be maintained. These diameters will be favorably of the order of a quarter to a third of the total thickness (e1+e2a+e2b) of the chamber bottom.

[0059] THE figures 2 And 9-11schematically detail the environment of the chamber bottom wall 118. Thus, it can be seen that the combustion chamber 101 is supplied with liquid fuel mixed with air. The liquid fuel is brought there by the fuel injector heads 112 engaged opposite (just upstream) the openings 119, along each axis 122a, after each having passed through the axial opening 37 of an annular cowling 39 fixed peripherally to the walls 114, 116. Initiated at the injector, the vaporization of the fuel is continued at the level of a venturi 38 and a pre-vaporization bowl 40 of generally annular shape, typically frustoconical, by the effect of the pressurized air coming from the aforementioned compressor.To pass through the opening 119 in question, the pressurized air passes through one or more radial swirlers 42 of the corresponding system 120, in order to ensure rotation of the fuel sprayed by the fuel injector head 112 coaxial with said system 120 in question. Each radial swirler may comprise an upstream swirler 42a and a downstream swirler 42b, adjacent. Each bowl 40 may have at its downstream end a collar 44 forming an outer rim, which may be radial. The swirlers could also be axial.

[0060] THE figures 2 , 10-11 show, by simple arrows, different air supply paths towards the hearth 115 and, figure 2 , by a double arrow, a fuel supply path towards this same hearth 115, which extends axially from the wall 118 of the chamber bottom, between the longitudinal walls 114, 116.

[0061] Each bowl 40 of the combustion air supply system 120 is mounted in (or surrounds, in a single-piece construction; see below) the opening 119 of one of the sectors of the chamber bottom wall 118.

[0062] The bowl 40 is crossed by the air and the fuel to ignite in the hearth 115.

[0063] Coming from the upstream compressed air (arrow 11), the compressed cooling air having circulated in the holes / pipes 128, can exit via: second holes 46 passing through the bowl 40, obliquely, in the direction of the axis 22a, and / or third holes 48 also passing through the bowl 40, just opposite the collar 44, to cool it, by impact.

[0064] The third holes 48 are substantially parallel to the axis 122a.

[0065] Before passing through the second 46 and third holes 48, the air having circulated in the holes / pipes 128 will preferably be released through the edge of the wall 118, at 128b (see figures 2 , 9-11 ), in order to supply an intermediate air distribution chamber 50, annular around the axis 122a. The distribution chamber 50 is closed upstream by a bent wall 52 connected both to the wall 118, towards its inner edge, and to the bowl 40.

[0066] The bent wall 52 may be crossed by at least one passage 54 for supplying, into the distribution chamber 50, air from the flow 111 but not having passed through the holes / pipes 128.

[0067] Thus, each combustion air supply system 120 may comprise at least one said supply passage 54 towards an external periphery of the bowl, and / or at least one spiral 42, provided respectively to be supplied with combustion air to be supplied inside the bowl 40, mixed with the air, coming from the chamber bottom wall 118, and having therefore passed through the second holes 46, for supplying air directly to the location of the opening 119 in question.

[0068] The relevant external periphery of the bowl 40 and the second holes 46 will be favorably located in its downstream part 40a which widens downstream, in order to distribute the air / fuel mixture in the combustion chamber 115.

[0069] If it is also desired to create a "cup" film for the upstream cooling of the (said surfaces oriented towards the chamber of the) internal 114 and external 116 walls, thanks to an impact flow coming from the bottom of the chamber 118, some of the outlets 128b, such as those 128b1, 128b2 figure 11 , will be able to pass through a remaining thickness of the wall 118, therefore across this thickness. These outlets 128b1, 128b2, connected to the holes / pipes 128, will be close to the edges 138a, 138b, while being directed downstream, in the immediate vicinity of the internal 114 and external 116 walls, respectively.

[0070] In all the above examples (see figures 2 , 9-11 ), the back wall 118 directly faces the inner hearth 115, without the interposition of a deflector plate, unlike the solution of the figure 1 .

[0071] In addition to additive manufacturing which may have made this possible (see above), this specificity is of course linked to the holes / pipes 128.

[0072] Concerning the connection between the bottom wall 118 and the combustion air supply system 120, several cases have been provided for: first, the bottom wall 118 and the system 120 can be welded together (in particular brazed); cf. figure 2 , alternatively, the bottom wall 118 and the system 120 can be monobloc (in particular if additive manufacturing); cf. figures 9 , 10-11 .

[0073] In both cases, the wall 118 was connected, towards the periphery of the opening 119, to the outer face of the flared part 40a of the bowl 40 and to the downstream end of the bent wall 52. In order to form the annular chamber 50, the upstream ends of the bowl 40 and the bent wall 52 were also connected together.

Claims

1. Combustion chamber (101) of a gas turbomachine for an aircraft, comprising: - longitudinal walls (114, 116) extending parallel to an axis (122a), - a hearth (115) where combustion takes place, - at least one bottom wall (118) connected to said longitudinal walls (114, 116) and extending transversely thereto, the bottom wall (118) comprising: -- at least one axial opening (119), -- holes (128) passing through it, for passing cooling air between at least one inlet (128a) and at least one outlet of said holes, the holes (128) extending along the bottom wall, inside the bottom wall, the outlet (128b) being located closer to said at least one opening (119) than the inlet, and -- at an outer periphery, a curved portion (138a, 138b) forming a rim, and - at least one combustion air supply system (120) comprising a bowl (40) mounted in said at least one opening (119), or integral with said at least one bottom wall (118), at the location of said rim (138a, 138b) the bottom wall (118) is fixed with the longitudinal walls (114, 116), - the combustion chamber being adapted to allow air to flow through it from upstream to downstream, passing successively: -- in said at least one axial opening (119) and said holes (128) in the bottom wall (118), then, -- in the hearth (115), - said rim (138a, 138b) being oriented upstream, said at least one inlet hole (128a) being located near a free end of the rim (138a, 138b), and characterised in that - said holes (128) opening onto the free edge (168a, 168b) of the rim of the bottom wall, at the location of the inlet orifices (128a).

2. Combustion chamber according to claim 1 wherein said holes (128) open onto the radially inner edge (168c) of the bottom wall, at the location of the outlet orifices (128b).

3. Combustion chamber according to any of the preceding claims, wherein at least some of said holes (128) individually define a sinuous line over at least a portion of their length.

4. Combustion chamber according to any one of the preceding claims, wherein the bowl (40) is traversed by second holes (46) and / or third holes (48) for passage of fluid, the second holes (46) and / or third holes (48) open into the hearth (115), and in the vicinity of the second holes (46) and / or third holes (48), open out at least some of the outlet orifices (128b) of at least some of said holes (128) of the bottom wall, so that air having passed through said holes (128) can also pass through said second and / or third holes.

5. Combustion chamber according to claim 4, wherein said at least one combustion air supply system (120) also comprises at least one supply passage (54) near an outer periphery of the bowl, and / or at least one twist (42), respectively adapted to be supplied with combustion air to be supplied to the inside of the bowl (40) mixed with air having passed through said second holes (46).

6. Combustion chamber according to any one of the preceding claims, wherein, at the location of the rim (138a, 138b), said at least one bottom wall (118) is fixed with the longitudinal walls (114, 116) by screws (32) which are circumvented by some of said holes (128) in the bottom wall.

7. Combustion chamber according to any of the preceding claims, wherein said bottom wall (118) directly faces the inner hearth (115).

8. Method of manufacturing, by additive manufacture, one said combustion chamber bottom wall according to any one of the preceding claims, wherein said holes (128) in the bottom wall (118) are made with a section (e1) smaller than the remaining thickness (e2a+e2b) of said bottom wall, on either side of said section.