FR2689965A1 - Combustion chamber having at least two fuel injection assemblies. - Google Patents

Abstract

The invention relates to a combustion chamber comprising a premixing chamber. According to the invention, the walls of this premix chamber comprise cells (26), the face of which limiting the premix zone is made of a first material resistant to a maximum operating temperature, and which are filled with a second material , whose melting temperature is between normal and maximum operating temperatures, and whose latent heat of fusion is greater than 400 kiloJoule / kilogram mass. One application is the production of a combustion chamber comprising injectors for idling and full throttle speeds.

Description

It is known to equip the combustion chambers, intended in particular for

  turbo-machines, two distinct groups of fuel injectors The fuel injectors of the first group are adapted to operate at idle speed, while on the contrary the fuel injectors of the second group are adapted to operating at full throttle Often, these second group fuel injectors are located at the bottom

a premix chamber.

  It has been found that, transiently, an undesired combustion could appear in this premix chamber, the walls thereof being consequently exposed to very high temperatures subjecting the structure to excessive thermal stresses, likely to damage definitely this structure. The invention intends, in the aforementioned framework, to propose a new arrangement allowing the structure to withstand, for short transient periods, a radiative flux

  thermal very high, of the order of a megawatt / m 2.

  The invention therefore relates to a combustion chamber, in particular for a turbo-machine, comprising at least a first assembly including a first fuel injection device and a first combustion zone, and adapted to the operation of the combustion chamber. at a first speed, such as the idling speed, and also comprising at least a second set including a second fuel injection device and a premix zone delimited by axial walls, this second set being preferably provided downstream of the premixing zone of a flame stabilization device and being adapted to the operation of the combustion chamber at a second speed, such as the full-throttle regime, said premixing zone being designed for operation at a predetermined temperature, but being liable, however, to be exposed for brief periods to a maximum temperature greater than the said temperature determined nature. According to the invention, said axial walls comprise, in their thickness, cells, at least the face limiting the premixing zone is made of a first material resistant to said maximum temperature, and (the cells) are filled with a second material, whose melting temperature is between said determined and maximum temperatures, and whose latent heat of fusion is greater than 400

kilo Joule / kilogram mass.

  The advantageous following arrangements are, moreover, preferably adopted: the axial walls are constituted by the assembly of two sheets, each having an assembly face, the assembly face of at least one of the two sheets comprising depressions delimited by contact edges, which are in sealing abutment on the assembly face of the other sheet, said cells being delimited by the parts of said assembly faces which comprise the depressions; the two sheets are held together by brazing said contact strips; each of said two sheets has depressions, which are grouped in pairs by a depression of one sheet and a depression of the other sheet to form a cell;

  the second material is sodium chloride.

  The main advantage lies in the exceptional resistance of the walls to short thermal stresses, but very strong

  intensity to which they are subjected.

  The invention will be better understood, and secondary features and advantages will become apparent in the course of

  description of achievements given below as an example.

  It is understood that the description and the drawings are not given

  as indicative and not limiting.

  Reference will be made to the accompanying drawings, in which Figure 1 is an axial section of a combustion chamber according to the invention; FIG. 2 is an enlargement of the detail A of FIG. 1 and FIG. 3 is a view similar to that of FIG.

  of an alternative embodiment also according to the invention.

  The combustion chamber shown in Figure 1 comprises a symmetry sensitive axis 1; a first annular inner wall 2, of axis 1, to which is connected a first particular annular wall 3, also of axis 1, contributing to define a premix chamber 4; a second annular inner wall 5, of axis 1, to which is connected a second particular annular wall 6, of axis 1, which completes the delimitation of the premixing chamber 4; an outer wall 7, annular axis 1; a bottom 8, which connects the outer wall 7 to the second inner wall 5; a flame stabilization device 9 placed at the outlet of the premixing chamber 4 of a known type such as, for example, one of those described and shown in FR-A-2 221 621; a fuel supply ramp 10, to which are connected a fuel injector 11, adapted to operate at idle speed, and a fuel injector 12, adapted to the full-throttle regime; an annular inner casing 13 of axis 1 and an annular outer casing 14 of axis 1 which delimit between them a space 15 inside which are contained the various annular walls already listed 2, 3 , 5, 6, 7, and which communicates upstream with a source of oxidant under pressure, shown schematically by the arrow F, and generally constituted by a helical compressor The combustion chamber 16 is delimited by the first inner wall 2, the second internal wall 5, the outer wall 7, and the bottom 8 In known manner, the inlet ports 17 of the primary oxidant and the openings 18 of diluting oxidant, formed in the second inner wall 5 and in the

  external wall 7, connect the space 15 to the combustion chamber 16.

  The fuel injectors 11, adapted to idle speed operation, pass through the bottom 8 and open into the combustion chamber 16. The fuel injectors 12, which are adapted to operating at full throttle, open into the fuel chamber. premix 4, the latter being in direct communication with the space 15, via its upstream mouth 19, located at the end of this premix chamber which is opposite to that, downstream, where is located the stabilization

flame 9.

  In principle, the normal operation of the combustion chamber corresponds to the realization, during operation in the full-throttle regime, of a fuel-oxidant mixture inside the premixing chamber 4, without combustion in this premixing chamber. 4, to the injection and ignition, in the area of the flame stabilization device 9, in the combustion chamber 16 of said mixture, and to the injection and ignition, in said enclosure of However, it has been found that sometimes unwanted combustion occurs inside the premix chamber 4 to allow the first particular wall 3 and the second particular wall 6 to support this flow. exceptionally large thermal radiative, but in short, each of these walls was carried out as defined below

with reference to Figures 2 and 3.

  According to the first embodiment of FIG. 2, each wall 3, 6 is constituted by the assembly of a first sheet, in one of the faces of which, depressions 21, delimited by contact strips 22, have been formed, with a second sheet 23, in one of the faces of which depressions 24, delimited by contact strips 25, have been formed The shapes of the contact selvedges 22, 25 correspond, so that said selvedges can be brought into contact with each other, and that the two sheets 20, 23 are finally assembled, for example by means of soldering

contact edges 22, 25.

  The sheets 20 and 23 are made of a first material resistant, of course, to the maximum temperatures at which said sheets can be exposed. It is generally a high temperature resistant super alloy, such as

  commonly used by turbo-machine manufacturers.

  Between the contact edges, cells 26 are formed and are filled with a second material defined below, introduced into

  the cells 26 at the time of assembly of the sheets 20 and 23.

  Before specifying the characteristics of said second material, it should be noted that the temperatures to which the particular walls 3 and 6 are exposed are between a determined temperature, corresponding to the normal operation of the combustion chamber, without combustion within the premixing chamber 4, and a maximum temperature, higher than said determined temperature and corresponding to the exceptional operation during which combustion is carried out inside said premixing chamber 4 As a guide, the normal temperature, determined may be the order of 7001 C, the maximum temperature rising to 9001 C for a few seconds. Under these conditions, the second material is chosen, so as to: a) be in the solid state at said determined temperature; b) to be in the liquid state at said maximum temperature, thus having a melting point between the determined and maximum temperatures; c) to have a latent heat of high melting, greater than 400 kilo Joule / kilogram, this precisely to absorb, during its fusion, the enormous amount of heat released by the accidental combustion carried out in the premix chamber 4, by hypothesis Without any increase in temperature during said melting. Among the materials suitable for this application, the sodium chloride is preferably chosen. Its latent heat of fusion is equal to 500 kilograms per kilogram, so that only a small amount is required. of this second material to prevent any damage to the walls 3 and 6 resulting from a possible abnormal rise in their temperatures. Thus, the thickness of the cells 26 may be between 1 and 1.5 mm. Thicknesses of the sheets 20 and 23

have similar values.

  An alternative embodiment is shown in FIG. 3, in which one of the sheets of FIG. 20 has been replaced.

  by a sheet 120 having no depression.

  The contact edges of the other sheet 23 are then in contact with the inner face 122 of the sheet 120.

  analogous to what has been specified in the description of the

  embodiment of FIG. 2, the cells delimited between the face 120 and the depressions 24 of the sheet 23, by the selvedges, are filled with the same second material as previously. The sheets 120 and 23 are furthermore made of the same first material. generally constituted by a super alloy resistant to

high temperatures.

  The invention is not limited to the embodiments described, but covers all the variants that could be

  brought without leaving their frame or their spirit.

  In particular, if it is necessary that the faces of the walls 3, 6, which delimit the premix chamber 4 are made in said first high temperature resistant material, the opposite face a priori less exposed to accidental high temperatures, could be achieved in a less resistant material In the examples described, the two sheets are

  made in the same first material.

1 bedroom of

Claims (4)

  combustion, in particular for turbo-machine, comprising at least a first set including a first fuel injection device (11) and a first combustion zone (16), and adapted to the operation of the combustion chamber at a first regime , such as the idling speed, and also comprising at least a second set including a second fuel injection device (12) and a premixing zone (4) delimited by axial walls (3, 6), this second set being preferably provided downstream of the premixing zone (4) of a flame stabilizing device (9) and being adapted to the operation of the combustion chamber at a second regime, such as the full-throttle regime, said zone Premix being designed for operation at a predetermined temperature, but being capable, however, of being exposed for brief periods to a maximum temperature greater than said temperature determined, characterized in that said axial walls (3, 6) comprise, in their thickness, cells (26), at least the face (20, 23; 120, 23) limiting the premix zone (4) consists of a first material resistant to said maximum temperature, and which (the cells) are filled with a second material, whose melting temperature is between said determined temperatures and maximum, and whose latent heat of   fusion is greater than 400 kilo Joule / kilogram mass.   Combustion chamber according to claim 1, characterized in that the axial walls are constituted by the assembly of two sheets (20, 23; 120, 23), each having an assembly face, the assembly face of at least one of the two sheets having depressions (21, 24; 24) delimited by contact strips (22, 25; 25), which bear tightly on the assembly face of the other sheet, said cells (26) being delimited by the parts of said assembly faces which include depressions.   3 combustion chamber according to claim 2, characterized in that the two sheets are held together by soldering said contact edges.   4 Combustion chamber according to any of the   claims 2 and 3, characterized in that each of the two   leaves has depressions, which are grouped by pair of a depression (21) of a sheet (20) and a depression (24)   from the other sheet (23) to form a cell (26).   Combustion chamber according to any one of   Claims 1 to 4, characterized in that the second material   consists of sodium chloride.