Combustion system having improved temperature resistance

Abstract

A combustion system is provided, including at least one combustion module and at least one source of combustible gas and oxidizing gas, the combustion module including a body including a single solid piece of material including two combustion chambers configured to be supplied with the at least one combustible gas and said one oxidizing gas; a first connector in contact with a first end of the body and being heat insulating, including first supply conduits configured to supply a combustible gas to the two combustion chambers, and first evacuation conduits configured to evacuate combustion gas from the two combustion chambers; and a second connector in contact with a second end of the body and being heat insulating, including second supply conduits configured to supply a combustible gas and an oxidizing gas to the two combustion chambers, and second evacuation conduits configured to evacuate combustion gas from the two combustion chambers.

Claims

1. A combustion system comprising at least one combustion module and at least one source of at least one combustible gas and one oxidizing gas, the at least one combustion module comprising: a body comprising a single solid piece of material including at least two combustion chambers configured to be supplied by the at least one source with the at least one combustible gas and said one oxidizing gas; a first connector in contact with a first end of the body, the first connector including first supply conduits configured to supply the at least one combustible gas to the at least two combustion chambers and being connected to the at least one source of the at least one combustible gas and the one oxidizing gas, and including first evacuation conduits configured to evacuate combustion gas from the at least two combustion chambers, a material of the first connector being heat-insulating relative to the single solid piece of material of the body; and a second connector in contact with a second end of the body, the second connector including second supply conduits configured to supply the at least one combustible gas and the one oxidizing gas to the at least two combustion chambers and being connected to the at least one source of the at least one combustible gas and the one oxidizing gas, and including second evacuation conduits configured to evacuate the combustion gas from the at least two combustion chambers, a material of the second connector being heat-insulating relative to the single solid piece of material of the body.

2. The combustion system according to claim 1, wherein the at least two combustion chambers are a first combustion chamber and a second combustion chamber, and the body further comprises two additional combustion chambers, wherein the first supply conduits are further configured to supply the at least one combustible gas to the two additional combustion chambers and are connected to the at least one source of the at least one combustible gas and the one oxidizing gas, and the first evacuation conduits are further configured to evacuate combustion gas from the two additional combustion chambers, the first supply conduits and the first evacuation conduits being disposed in an alternating arrangement, and/or wherein the second supply conduits are further configured to supply the at least one combustible gas to the two additional combustion chambers and are connected to the at least one source of the at least one combustible gas and the one oxidizing gas, and the second evacuation conduits are further configured to evacuate the combustion gas from the two additional combustion chambers, the second supply conduits and the second evacuation conduits being disposed in an alternating arrangement.

3. The combustion system according to claim 1, wherein the at least two combustion chambers are connected to supply conduits of at least one of the first and second connectors and to evacuation conduits of at least one of the first and second connectors.

4. The combustion system according to claim 1, wherein the at least one source of the at least one combustible gas and the one oxidizing gas is a mixture of gases.

5. The combustion system according to claim 1, wherein the at least one source of the at least one combustible gas and the one oxidizing gas is a mixture of H.sub.2 and O.sub.2 or H.sub.2 and air.

6. The combustion system according to claim 1, wherein the single solid piece of material of the body is SiC, and wherein the material of the first connector and the material of the second connector are zirconium oxide, mullite, or alumina.

7. The combustion system according to claim 1, wherein the combustion system further comprises tubes connecting the at least one source to the first and second connectors, a material of the tubes being a high-temperature steel or a NiCo alloy.

8. The combustion system according to claim 1, wherein the at least two combustion chambers comprise at least one ignition catalyst.

9. The combustion system according to claim 1, where at least one of the first connector and the second connector further include projections on at least one end face thereof, the projections being removably insertable, respectively, into the first end of the body and the second end of the body.

10. The combustion system according to claim 1, wherein the body has a substantially rectangular parallelepiped shape including two faces of larger surfaces relative to other faces of the shape, and being connected by two lateral faces and two end faces, the at least two combustion chambers emerging at the two end faces.

11. A hybrid solar system, comprising: a concentrator configured to concentrate solar radiation and comprising at least one mirror or a Fresnel lens; the combustion system according to claim 1, being arranged such that concentrated solar radiation illuminates one face of the body; a converter configured to convert thermal energy into electricity on a face of the body that is opposite to the illuminated one face; and a controller configured to control combustion in the at least one combustion module as a function of the concentrated solar radiation.

12. The hybrid solar system according to claim 11, wherein the illuminated one face is functionalized by a high-temperature solar absorber configured for heating by absorption of solar radiation.

13. The hybrid solar system according to claim 11, wherein the illuminated one face is functionalized by an interferential absorber including at least one of TiAlN, AN, and SiO.sub.2, or a nanostructured refractory material including at least one of molybdenum, tantalum, and tungsten.

14. The hybrid solar system according to claim 11, wherein the converter comprises at least one thermophotovoltaic cell; and wherein the face of the body that is opposite to the illuminated one face is functionalized with a selective emitter, such that emitted infrared radiation is in a wavelength domain in which the at least one thermophotovoltaic cell has a maximum conversion efficiency.

15. The hybrid solar system according to claim 11, wherein the converter comprises at least one thermophotovoltaic cell, and wherein the face of the body that is opposite to the illuminated one face is functionalized with a stack of tungsten and Al.sub.2O.sub.3 or of silicon and SiO.sub.2, or a nanostructured refractory material including at least one of molybdenum, tantalum, and tungsten, such that emitted infrared radiation is in a wavelength domain in which the at least one thermophotovoltaic cell has a maximum conversion efficiency.

16. A method of manufacturing a combustion system according to claim 1, comprising: a) manufacturing the body comprising the single solid piece of material including the at least two combustion chambers; b) manufacturing the first connector and the second connector, including providing the first supply conduits, the first evacuation conduits, the second supply conduits, and the second evacuation conduits; c) assembling the first connector and the second connector in contact with the first end of the body and the second end of the body, respectively; and d) connecting the first connector and the second connector to the at least one source of the at least one combustible gas and the one oxidizing gas.

17. The method according to claim 16, wherein during step b) the first and second connectors are manufactured by injection molding of ceramic powder, and/or wherein during step c), the first and second connectors are assembled by welding or brazing.

18. The method according to claim 16, further comprising a step of depositing a catalyst in the two combustion chambers.

19. The method according to claim 18, the catalyst is deposited by liquid phase impregnation or chemical vapor deposition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be better understood with the help of the description that follows and the appended drawings, in which:

(2) FIG. 1 is a schematically represented top view of an example of embodiment of a combustion system,

(3) FIGS. 2A and 2B are detailed views of variants of connections at a connector, the body and supply and evacuation tubes,

(4) FIG. 3 is a graphic representation of the temperature variation along a longitudinal direction extending between the two connectors of the module of the system of FIG. 1 and between the two connectors of a module in which one of the connectors only serves for supply with gas,

(5) FIG. 4 is a top view of the system of FIG. 1 in which the temperature within the module is schematically symbolized by grey levels,

(6) FIG. 5 is a top view of a combustion system in which one end is dedicated to supply and the other end is dedicated to evacuation, in which the temperature within the module is schematically symbolized by grey levels, by way of comparison with FIG. 4,

(7) FIG. 6 is a schematic representation of a hybrid solar system implementing the combustion system.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(8) In FIG. 1 may be seen an example of combustion system comprising a combustion module M1 and a source of at least one combustion gas S1. The combustion module M1 comprises a body 2 including a plurality of combustion chambers C1, C2, C3, C4, a first connector 6 and a second connector 8.

(9) The body 2 is advantageously one-piece, the combustion chambers being formed in the body.

(10) The body 2 extends along a longitudinal direction X and has a first longitudinal face 2.1 or first end face 2.1 and a second longitudinal face 2.2 or second end face 2.2. In the example represented, the body has the shape of a rectangular parallelepiped. It further comprises upper and lower faces 2.3 (not visible) which have a larger surface and two lateral faces 2.4.

(11) The combustion chambers C1, C2, C3, C4 extend parallel to a direction X.

(12) Preferably, the combustion chambers C1, C2, C3, C4 are spread out the most towards the exterior in a transversal direction with respect to the longitudinal direction X so as to compensate lateral thermal losses and so as to assure uniform heating of the body.

(13) In the example represented, each chamber C1, C2, C3, C4 is in the form of a channel of which a first end emerges in the first face 2.1 and of which a second end emerges in the second face 2.2. Preferably the surfaces of each combustion channel are covered with a combustion catalyst material, such as platinum.

(14) A combustion module comprising a single combustion chamber and/or chambers having other shapes does not go beyond the scope of the present invention.

(15) The first connector 6 comprises as many through conduits 10.1 to 10.4 as combustion chambers C1 to C4, each of the conduits 10.2 to 10.4 being intended to be aligned with one end of a combustion chamber C1 to C4.

(16) The second connector 8 also comprises as many through conduits 11.1 to 11.4 as combustion chambers C1 to C4, each of the conduits 11.1 to 11.4 being intended to be aligned with another end of a combustion chamber C1 to C4.

(17) In the example represented and in a preferred manner, the conduits 10.1 and 10.3 and the conduits 11.2 and 11.4 are connected to the source S1 of combustible gas and oxidizing gas. The conduits 10.2 and 10.4 and 11.1 and 11.3 are intended to evacuate the combustion gases.

(18) In the example represented, the conduits of the connectors are connected to the same source of gas, but a system with several sources of gas, or even different gases does not go beyond the scope of the present invention. Thus each of the first 6 and second 8 connectors serves both for the supply of the chambers and for the evacuation of the chambers C1-C4.

(19) The chambers C1 and C3 are thus supplied with gas with a view to combustion via the connector 6 through the face 2.1 of the body and the chambers C2 and C4 are supplied with gas with a view to combustion via the connector 8 through the face 2.2. The combustion gases of the chambers C1 and C3 are thus evacuated via the connector 8 and through the face 2.2 of the module and those of the chambers C2 and C4 via the connector 6 through the face 2.1.

(20) Thus each connector 6, 8 is crossed through by combustion gases and by the combustible gas or gases and the oxidizing gas or gases which are at a temperature well below that of the combustion gas. The thermal gradient through each of the connectors is reduced compared to that of a connector serving uniquely for supply. Moreover, by alternating the supply and evacuation conduits there is better temperature homogeneity of the connector in the transversal direction, as well as in the body.

(21) Preferably, in each connector a supply conduit alternates with an evacuation conduit, the two conduits balancing each other, which makes it possible to obtain even more homogenous temperature in the transversal direction.

(22) Preferably, a catalyst capable of initiating combustion is present in the chambers. It is advantageously deposited on the inner surface of the combustion chambers. It may be for example constituted of platinum, rhodium or combustion catalyst oxides.

(23) In a variant, combustion may also be initiated by an input of external energy such as for example a spark, a heating resistor. In the case of a module used in a hybrid manner which associates both solar energy and energy stemming from combustion, the energy may be simply that provided by the concentration of solar radiation on the body.

(24) The first and second connectors are made of a heat insulating material such that they limit heat transfer from the connection module to the exterior in the direction X. The material of the first and the second connectors have a thermal conductivity substantially lower than that of the material of the body 2, advantageously at least five times lower than that of the body.

(25) The material of the first connector may be the same as that of the second connector or a different material.

(26) In the present application heat insulating material is taken to mean a material of which the thermal conductivity at room temperature is less than 50 W/m.K, preferably less than 10 W/m.K.

(27) The heat conducting material of the body may have a thermal conductivity at room temperature greater than 30 W/m.K.

(28) Preferably, the first and second connectors are made of zirconium oxide. In a variant it may be provided that they are made of aluminum oxide, mullite or any other material capable of assuring sufficient heat insulation.

(29) The body is preferably made of SiC. In a variant it may be made of steel, cordierite, alloy for example nickel/cobalt.

(30) Tubes 12 connect the source of combustible gas and oxidizer and the combustion chambers, they are connected to the conduits 10.1 and 10.3 at a first end face 6.1 of the first connector 6, the first connector 6 being connected to the body by a second end face 6.2.

(31) In the same way, tubes 12 connect the source of combustible gas and oxidizer and the combustion chambers C1 to C4, they are connected to the conduits 11.2 and 11.4 at a first end face 8.1 of the second connector 8, the second connector being connected to the body by a second end face 8.2.

(32) The evacuation gases are preferably collected in a reservoir or guided to the exterior via conduits 13 connected to the conduits 10.2 and 10.4 and 11.1 and 11.3 via the first faces 6.1 and 8.1 of the first and second connectors respectively.

(33) The conduits 12 and 13 are for example made of high temperature steel, or alloy such as NiCo alloys. Due to the presence of heat insulating connectors interposed between the body and the combustible gas supply tubes 12, the temperature of the tubes is reduced compared to that of the combustion chambers C1 to C4 and the risks of auto-ignition are substantially reduced. The heat insulation procured by the two connectors 6, 8 is due to the heat insulating material and to the dimensions of the connectors, notably in the direction X.

(34) In FIG. 2A may be seen a detailed view of the module of FIG. 1 at the connection between the first connector 6 and the body 2, on the one hand, and between the conduits 10.1 and 10.2 of the first connector 6 and the gas supply conduits 12 and the evacuation conduits 13, on the other hand.

(35) In the example represented, the second end face 6.2 of the first connector 6 and the longitudinal face 2.1 of the body are in planar abutment and secured to each other so as to assure a leak tight connection between the borings 10 and the combustion chambers C1 and C2. The body 2 and the connector 6 are made integral with each other for example by welding or brazing.

(36) Moreover in the example given, the ends of the conduits 10.1 and 10.2 emerging in the first end face 2.1 comprise a portion of larger diameter 15 making it possible to accommodate the ends of the supply tubes 12 and the ends of the evacuation tube 13.

(37) In FIG. 2B may be seen a variant of embodiment of the first connector 6 in which the second end face 6.2 comprises annular projections 14. Each annular projection 14 runs alongside one emerging end of the conduits 10.1 and 10.2 in the end face 2.2. The annular projections 14 penetrate into one end of the chambers emerging in the end face 2.1 by insertion. The end of the combustion chamber has a sufficient diameter to receive this annular projection 14. Thanks to this variant, the connection leak tightness between the first connector and the body is improved, its formation is simplified and alignment between the conduits 10.1 and 10.2 and the chambers C1 and C2 is simplified. The assembly of the materials is carried out for example by brazing.

(38) The examples of connection between the first connector 6 and the body 2 represented in FIGS. 2A and 2B also apply to the connection between the second connector 8 and the body 2.

(39) For example, the combustion chambers may be supplied by a H.sub.2/air mixture. In a variant they may be supplied by a H.sub.2/O.sub.2 mixture. In a further variant, the combustion chambers may be supplied by a H.sub.2/CH.sub.4/air mixture, the quantity of CH.sub.4 being small compared to that of H.sub.2.

(40) In a further variant, the combustion chambers may be supplied by a CH.sub.3OH/air mixture. It is then preferable to preheat the intake mixture, for example to at least 200 C. This preheating may advantageously be obtained by solar energy in the case of a combustion system implemented in a hybrid solar system.

(41) The combustible gas and the oxidizer are then mixed before being conveyed to the first and second connectors 6, 8. Advantageously, it may be provided that the conduits of the connectors intended for supply comprise means for improving the mixing of the gases, for example a porous structure.

(42) The operation of the combustion module will now be described.

(43) The combustion chambers C1 and C3 are supplied with gas by the tubes 12 via the conduits 10.1 and 10.3 of the first connector 6, and the combustion gases are evacuated by the tubes 13 via the conduits 11.1 and 11.3 of the second connector 8. The combustion chambers C2 and C4 are supplied with gas by the tubes 12 via the borings 11.2 and 11.4 second connector 8 and the combustion gases are evacuated by the tubes 13 via the conduits 10.2 and 10.4 of the first connector 6.

(44) Thus each connector is both crossed through by cold gases coming from the exterior and hot gases coming from the combustion chambers.

(45) In FIG. 3 may be seen two graphic representations of the variation in temperature T in C. as a function of the position in meter along the longitudinal direction X in a combustion module, the origin of the abscissa being the first end face 6.1 of the first connector 6.

(46) Curve A is the representation of the temperature in the module M1 of FIG. 1 in which the supply and the evacuation are crossed and curve B is the representation of the temperature in a module in which the supply only takes place via a connector and the evacuation only takes place via the other connector. The first end face of the supply connector of the module of curve B is at the abscissa O.

(47) An air and H.sub.2 mixture is burned in the combustion chambers.

(48) The two connectors are made of zirconium oxide and have a dimension in the direction X of 10 mm and the body is made of SiC and has a dimension in the direction X of 30 mm, a dimension in a transversal direction to the direction X of 30 mm and a distance between the upper face and the lower face of 5 mm. The module comprises 4 or 6 combustion chambers of 1.5 mm diameter.

(49) Zone I corresponds substantially to the first connector 6, zone II corresponds substantially to the body 2, zone III corresponds substantially to the second connector 8.

(50) It may firstly be noted in curve A that the variations in temperature in the first and second connectors are substantially symmetrical. In the first connector 6, the temperature increases by 94 C./mm from the first end face 6.1 to the body 2 and in the second connector 8 it increases by 88 C./mm from the first end face 8.1 to the body 2.

(51) On the contrary in curve B, it may be noted that the temperature gradient is substantially more important in the supply connector, which only sees gas intended to be burned in the chambers, than in the evacuation connector. The temperature varies by 116 C./mm in the supply connector whereas it varies by 70 C./mm in the evacuation connector.

(52) Thanks to the invention, the two connectors are subjected to substantially identical or very similar temperature gradients and of reduced values, which reduces the risks of damaging the connectors by thermal shock or simply resulting from thermomechanical stresses generated by the thermal gradients.

(53) Moreover, since the two connectors have the same thermal stresses, the risks of damage within the module are reduced. The module thus offers greater thermomechanical resistance and a longer lifetime of the module and thus of the thermal system.

(54) Moreover, it may be noted that the temperature in the body of the module of FIG. 1 is higher than that in the module with supply and evacuation via separate connectors. In fact, in the case of the module M1, the maximum temperature of the combustion module is 1756 C. and that of the lower surface 1741 C. These two temperatures are substantially greater than those of the module in which supplies and evacuations are carried out via separate connectors, for which case they are respectively 1742 C. and 1727 C. This is due to the fact that the establishment of a smaller temperature gradient between the body and connector makes it possible to limit slightly thermal losses and to obtain better temperature uniformity of the module M1.

(55) It may also be advantageously noted that the temperature at the first end faces 6.1 and 8.1 of the first and second connectors 6, 8 respectively is less than 600 C. Yet, it is the temperature above which auto-ignition generally takes place in stoichiometric conditions. The risks of auto-ignition in the supply tubes 12 are thus reduced or even eliminated.

(56) In FIG. 4 the main temperature zones in the module are schematically represented by grey levels. It may be seen that the body 2 of the module M1 has the highest temperature, then the two connectors 6, 8 have a relatively homogeneous temperature in the transversal direction on account of the alternating arrangement of the supply and evacuation conduits. In FIG. 5, the main temperature zones in the module M0 of curve B are represented by grey levels.

(57) In a variant, in the first and second connectors all the supply conduits could be grouped together on one side and all the evacuation conduits could be grouped together on the other side, the module would have less good temperature homogeneity in the transversal direction but, nevertheless, the temperature gradients in the two connectors would be smaller compared to those of the connectors of the module of curve B.

(58) In a further variant, the supply and evacuation conduits could be grouped together by groups of 2 or 3 for example, the groups being alternating.

(59) A combustion system in which the first and second connectors are not identical, one being similar to that of FIG. 1 and the other being similar to one of the above variants, does not go beyond the scope of the present invention.

(60) In the example of FIG. 1, the body comprises four combustion chambers. In a variant it could only comprise a single chamber with several supply inlets and several evacuation outlets spread out in the two connectors.

(61) Preferably, at least for application to a solar system, several combustion chambers are spread out in a single plane parallel to the lower and upper faces to assure conduction of heat from the upper face to the lower face.

(62) This combustion module may be advantageously implemented to produce a hybrid solar system in which the upper face is subjected to solar radiation and the lower face is in contact with thermoelectric modules, the heat produced by the combustion chamber making it possible to compensate variations in sunlight and to have a substantially continuous and constant operation of the thermoelectric modules. In a variant, the lower face may be positioned opposite a thermophotovoltaic cell converting the infrared radiation from the lower face into electricity.

(63) In FIG. 6 may be seen a schematic representation of an example of a solar system comprising a combustion module according to the invention. Solar radiation is shown schematically by the arrows R.

(64) The solar system comprises means for concentrating 18 solar radiation, a combustion module M1 arranged opposite the concentration means 18 with respect to the sun such that the upper face of the body is illuminated by the concentrated solar radiation and thermoelectric modules MTH of which the hot face is in thermal contact with the lower face of the body of the module. In a variant, this module MTH may comprise one or more thermophotovoltaic cells placed facing the lower face of the combustion module and transforming the infrared radiation into electricity.

(65) The system comprises means for controlling UC combustion of the chamber in concentrated solar radiation operation so as to maintain a substantially constant temperature on the lower face of the body of the combustion module or to adjust the value thereof so as to control the electrical power supplied by the module.

(66) Preferably, the upper surface of the module intended to receive the concentrated solar flux, and in particular the upper surface of the body, is functionalized with a high temperature solar absorber to enable heating by absorption of solar radiation. For example it may be an interferential absorber deposited on the upper surface, such as TiAlN/AlN/SiO.sub.2 or a nanostructured refractory material such as molybdenum, tantalum or tungsten.

(67) Preferably, the lower surface of the module, in particular the lower surface of the body, is functionalized with a selective emitter such as a stack of W/Al.sub.2O.sub.3 or Si/SiO.sub.2 or such as a nanostructured refractory material such as molybdenum, tantalum or tungsten.

(68) The lateral surfaces of the module, in particular those of the body, may advantageously be functionalized using a low emissivity material such as a refractory material.

(69) The means for concentrating radiation are for example a mirror or Fresnel lens.

(70) The thermoelectric modules may for example be replaced by any device capable of converting heat into electricity or any other form of energy, such as for example the aforementioned thermophotovoltaic cells.

(71) The operation of the solar system will now be described.

(72) When solar radiation is sufficient it heats the body of the combustion module striking its upper face after having been concentrated.

(73) Heat is transmitted by conduction through the body up to the lower face thanks to the material of the body between the combustion chambers, a thermal gradient then appears in the thermoelectric modules and electricity is produced.

(74) If radiation is insufficient, for example in the event of cloudy periods or at night time, gases are burned in the combustion chambers, heat is produced, which completes that produced by solar radiation or offsets its absence. A thermal gradient then appears in the thermoelectric modules and electricity is produced. In the case of a thermophotovoltaic cell replacing the thermoelectric module the infrared radiation is transformed into electricity.

(75) An example of method of production will now be described.

(76) The body and the first and second connectors are firstly produced by machining.

(77) During a following step, drillings are made in the body in order to form the combustion chambers.

(78) Then the supply and evacuation conduits 10 and 13 are drilled in the first and second connectors respectively.

(79) In the case where the conduits could be of complex shape, the connectors may be produced by a technology of injection molding of ceramic power, more particularly micro-CIM technology to mold for example zirconium oxide, aluminum oxide, silica nitride, mullite. For example, the ceramic powder is mixed with components making it possible to inject the mixture into a mold. Then a method known as debinding makes it possible to remove from the material components other than the desired ceramic. Finally high temperature annealing makes it possible to finalize the production of the ceramic part.

(80) During a following step, the combustion catalyst may be deposited on the inner surface of the combustion chambers by liquid impregnation or by chemical vapor deposition.

(81) During a following step the body and the connectors are made integral for example by brazing or by welding.

(82) During a following step, the supply and evacuation tubes are secured to the connectors for example by welding or by brazing.

(83) It is possible to envisage securing the tubes to the connectors, before securing the connectors to the body.

(84) As has been described above, the combustion system according to the invention is particularly suited to the production of a hybrid solar system in which the combustion chamber(s) make it possible to maintain a constant temperature with a view to thermoelectric conversion.

(85) The combustion system may be used to generate heat on the basis of micro-combustion or meso-combustion.

(86) Another application may be the production of combustion microsystems to obtain heat micro-sources.

(87) Another application may be the production of combustion microsystems for micro-propulsion systems.