HYDROGEN-AIR MIXTURE INJECTION METHOD FOR TURBOMACHINE BURNER

Abstract

An injection method for an injection device in the combustion chamber of an aircraft turbomachine, said injection device comprising an internal channel (6) surrounded by an external annular channel (8), said channels opening into said combustion chamber (4, 4') of said gas turbine, characterized in that it comprises an injection of a dihydrogen-air mixture (12a) with a hydrogen content exceeding the stoichiometric ratio into said internal channel (6) and an injection of air into said external annular channel (8) so as to produce, at the outlet of said internal channel (6), a first flame front (30) resulting from rich combustion surrounded by a second flame front (31) resulting from lean combustion. Figure 3

Description

Title of the invention: METHOD FOR INJECTING HYDROGEN-AIR MIXTURE FOR TURBOMACHINE BURNER technical field

[0001] This disclosure relates to the field of methods for supplying gas turbine injection devices such as aircraft turbomachinery powered by dihydrogen and air. This includes, in particular, civil and military aeronautical applications: helicopters, VTOLs, drones, APUs, turbogenerators, fixed-wing aircraft for recreational, business or commercial aviation, turbojets or turboprops. Previous technique

[0002] The propulsion sector, and in particular the aeronautical sector, faces major environmental challenges. The interest in using hydrogen combustion rather than kerosene is growing stronger because hydrogen combustion would avoid carbon-based pollutant emissions such as carbon dioxide, carbon monoxide, unburned hydrocarbons, and fine particles and smoke.

[0003] A principle for micro-mixing air-dihydrogen burners is known. Burners manufactured according to this principle do not guarantee the absence of flashback in the dihydrogen injection device and have a complex geometry. Such burners have a high manufacturing cost, a high pressure drop, and are specific to a given combustion chamber architecture.

[0004] At the level of injection and combustion, two main technological configurations for hydrogen-air injection systems applied to gas turbines exist, namely lean injection systems, and rich injection systems.

[0005] More generally, it is important to bear in mind that lean-burn fuel systems tend to generate significant thermoacoustic instabilities that can damage these systems, whereas stable combustion is necessary to avoid impairing engine performance. Rich-burn fuel systems, on the other hand, tend to emit more pollutants than lean-burn systems if they are not properly designed. Technical problem

[0006] The use of hydrogen involves several issues to be taken into consideration at the combustion chamber level:

[0007] Under equivalent thermodynamic conditions in terms of pressure, temperature, and air-fuel ratio, the The adiabatic temperature of the flame from a hydrogen-air combustion is higher than that of the flame from a kerosene-air combustion.

[0008] Similarly, the flame speeds resulting from hydrogen-air combustion are higher than for kerosene-air flames. A high flame speed can lead to flashback problems in injection systems, particularly at the boundary layer level, and cause serious damage to these systems, or even cause safety problems.

[0009] However, the flammability limits of hydrogen are more extensive than those of kerosene and allow a hydrogen-air mixture to be ignited at lower or higher enrichments than for kerosene, which can ultimately allow lower flame temperatures to be achieved than with the use of kerosene.

[0010] Finally, the combustion of hydrogen with air tends to emit much more noise than conventional kerosene combustion and can therefore generate significant noise pollution at airports. Description of the invention

[0011] The present document proposes a premixed rich injection process dedicated to the combustion of dihydrogen and air, enabling the technical problems presented above to be addressed.

[0012] More specifically, the present disclosure proposes an injection method, for an injection device in a combustion chamber of an aircraft turbomachine, said injection device comprising an internal channel surrounded by an external annular channel, said channels opening into said combustion chamber of said gas turbine, the method comprising an injection of a dihydrogen-air mixture with a hydrogen content greater than the stoichiometric dosage into said internal channel and an injection of air into said external annular channel so as to produce, at the outlet of said internal channel, a first flame front from a rich combustion surrounded by a second flame front from a lean combustion, after ignition of the mixture.

[0013] The process in which the injection is carried out continuously after ignition in order to operate the turbine makes it possible to reduce the temperature of the flame fronts which reduces the NOX content of the burnt gases and reduces wear on the injector.

[0014] The features described in the following paragraphs correspond to embodiments that can be implemented independently of each other or in combination with each other as appropriate:

[0015] The dihydrogen-air mixture can have a hydrogen content greater than 2.

[0016] Advantageously, said dihydrogen-air mixture may have a hydrogen content greater than or equal to 4.

[0017] An air flow in the external annular channel can be chosen such that the overall richness at the outlet of the internal and external annular channel assembly is fixed between 0.15 and 0.5 depending on the operating points of the turbomachine.

[0018] The injection of the dihydrogen / air mixture and the injection device can be configured to create at the outlet of the internal channel said first flame front, resulting from the rich combustion of said mixture and to hook it on a peripheral lip of the internal channel.

[0019] The hydrogen content of the mixture can be chosen so that said rich combustion takes place with a flame front temperature below 1800 K, which preserves the combustion chamber.

[0020] The hydrogen content of the mixture can be chosen so that the first flame front is laminar and has a Lewis number greater than 1, limiting thermo-diffusive instabilities and thus avoiding flashback phenomena.

[0021] The mixture burned in the first flame front generates residual gases which are advantageously burned in the second flame front stabilized by the supply of air from the external annular channel.

[0022] The richness of the second flame front is such that the second flame front can be maintained at a temperature below 1800K.

[0023] The air injected through the annular channel can be rotated by an annular screw so as to make the second flame front turbulent and so that this second flame front is not attached to the lip of the internal channel.

[0024] Advantageously, positioning the downstream end of the internal channel upstream of the downstream end of the external annular channel optimizes the mixing between the gases from the first combustion and the air injected through the external channel. Brief description of the drawings

[0025] Other features, details and advantages of the invention will become apparent from the following detailed description of non-limiting embodiments and from the analysis of the accompanying drawings, in which:

[0026] [Fig-1] shows a turbomachine comprising an injection device arranged in an annular base of an annular combustion chamber according to three configurations;

[0027] [Fig.2] shows a first schematic example in side view section of an injection device to which the process of the present disclosure applies;

[0028] [Fig.3] shows a schematic view of the device of [Fig.2] in a combustion situation;

[0029] [Fig.4] shows a plurality of possible configurations (figures A, B, C, D, E) of internal channel of a device to which the process of the present disclosure applies;

[0030] [Fig.5] shows a plurality of examples of channel output configurations annular (figures A, B, C) for a device to which the process of this disclosure applies. Description of the implementation methods

[0031] The drawings and the description below contain elements that can not only serve to better understand the invention, but also contribute to its definition, if necessary.

[0032] Reference is now made to [Fig. 1], which represents three examples of configurations for the implantation of an injection device 2 on a turbomachine 1, depending on the orientation of the annular bottom of an annular combustion chamber 4, 4', 4" of the turbomachine: either the combustion chamber 4" is oriented substantially along a longitudinal axis X, or the combustion chamber 4 is oriented at an acute angle to this longitudinal axis, or the combustion chamber 4' is transverse to said longitudinal axis X. In all cases, the injection device 2 is implanted between a compressor 101 and a high-pressure turbine 102, 103, 104, on an annular bottom of the annular combustion chamber 4, 4', 4" or on an external shell.

[0033] The injection device can be, as illustrated in [Fig. 2], an injection device comprising an internal channel 6 and an external annular channel 8. The external channel 8 is centered on the internal channel 6, and in the case of tubular channels, the internal channel 6 and the external annular channel 8 are coaxial. These channels open into the combustion chamber 4, 4', 4" of the device in [Fig. 1]. The internal and external channels have a circular cross-section. An ignition device, not shown, ignites the gases exiting the channels to initiate combustion.

[0034] This injection device 2 is used in the present disclosure in a configuration in which a rich dihydrogen-air mixture is injected into the internal channel 6 while air is injected into the external channel 8. As a result, the combustion comprises a first combustion rich in dihydrogen at the outlet of the internal or central channel 6. and a second combustion, called lean, which is carried out around a flame created by the first combustion.

[0035] For injection into the internal channel 6 and combustion at the outlet of this channel, injection and combustion are said to be rich when there is excess dihydrogen compared to a stoichiometric combustion between dihydrogen and dioxygen from the air, and lean when there is excess dioxygen compared to this stoichiometric combustion. Stoichiometric combustion is itself defined as combustion in which there are the correct number of hydrogen and oxygen atoms necessary to consume all the fuel, leaving only water and dinitrogen in the products. combustion.

[0036] According to [Fig.3], the present invention thus provides an injection method which comprises an injection of a dihydrogen-air mixture 12a with a hydrogen richness greater than the stoichiometric dosage into the internal channel 6 of the injection device and an injection of air 26a into the external annular channel 8 so as to produce, at the outlet of said internal channel 6, a first flame front 30 resulting from a rich combustion surrounded by a second flame front 31 resulting from a lean combustion.

[0037] The internal channel 6 then forms a hydrogen-air rich mixture injection tube 12a and the external annular channel 8 forms an air injection tube 26a.

[0038] The rich mixture 12a of air and dihydrogen is injected from an inlet 10 located at an upstream end of the internal channel 6.

[0039] The internal channel 6 has an internal diameter d. The choice of the internal diameter d of the channel depends on a desired thermal power.

[0040] Returning to [Fig. 2], a downstream end 16 of the internal canal 6 is arranged upstream with respect to a downstream end 24 of the external annular canal 8. The downstream end 24 of the external annular canal 8 is arranged at a distance r from the downstream end 16 of the internal canal 6 downstream. This external annular canal 8 has an internal diameter D.

[0041] The external annular channel 8 is configured to receive a second gas, which is air 26a. This gas enters the external annular channel through an inlet 26a arranged at the upstream end of said external annular channel.

[0042] An annular spiral 28 is housed at the upstream end of the external annular channel 8. This spiral can be radial or axial. This annular spiral 28 is arranged at a distance L from the downstream end 36 of the external annular channel 8. The air 26a passing through the external annular channel is set into rotation by the external spiral 28. This generates a vortex assembly that will help to detach the second flame front from the outlet of the central channel.

[0043] The hydrogen-air premix 12a is injected into the internal channel 6, formed by a tube creating a central injection conduit. The premix has a richness greater than two, i.e., greater than 2 masses of hydrogen to 1 mass of air, and can even have a richness greater than four in certain operating configurations.

[0044] The pure air 26a injected into the annular channel 8 around the internal channel 6 is injected in a calculated quantity so as to target an overall injection richness between 0.15 and 0.5, which amounts to an overall lean combustion. The pure air 26a is set in rotation in the annular channel 8 by the external axial or radial auger 28 located upstream of the outlet plane 16a of the downstream end 16 of the central injection duct. rich dihydrogen-air mixture.

[0045] The lip 16 of the internal canal 6 is here in recess relative to the exit plane 24a of the annular canal 8.

[0046] The operation of the injection device is described below, based on [Fig.3]:

[0047] The injection of the rich dihydrogen-air premix 12a into the internal channel 6 allows, after ignition, the creation at the outlet of the internal channel 6 of a first flame front 30 resulting from the rich combustion of said mixture. This flame front adheres to the lip 16 of the internal channel 6. This rich combustion, for example with a richness greater than 2, takes place with a flame front temperature below 1800 K in order to avoid generating nitrogen oxides. This flame front 30 is laminar and is not subject to thermal diffusion instabilities due to a Lewis number greater than 1.

[0048] The injection of air 26a at the level of the external annular channel 8 allows for the rapid dilution and confinement of the burnt gases from the combustion of the rich premix. The presence of a strong turbulent shear layer reduces the local richness. This mixture is then burned and generates a second flame front 31 of lean combustion. This flame front remains stabilized thanks to the vortex quench caused by the air supply and thanks to the high reactivity of dihydrogen despite the strong stretching imposed on the flame. This second flame front from lean combustion is also at a temperature below 1800 K, limiting the formation of nitrogen oxides. The flame front 31 is turbulent and is not attached to the lip 16 of the internal channel 6.The length of the flame will depend on the conditions of entry of the fuels and oxidants and in particular on the ratio of the quantities of momentum, the indentation of the internal channel relative to the external annular channel, and the presence of vortices in the flame.

[0049] The creation of these two flame fronts, a rich flame 30 and a lean flame 31, allows the thermo-acoustic load from combustion to be distributed over a larger surface area, and therefore reduces combustion noise. Similarly, stabilizing the two flame fronts at the burner lips divides the thermo-acoustic loads associated with combustion and reduces the noise generated.

[0050] The combustion process of this document thus achieves a staged combustion of hydrogen in order to bypass the nitrogen oxide formation zone by means of the combustion of the dihydrogen-rich air premix in a first zone, the internal flame 30, and the combustion of the residual gases in a second zone, the flame 31 around the flame 30.

[0051] The risk of flashback is limited with rich combustion because the first flame front does not contain instabilities. thermo-diffusive. The speed of the first flame is therefore not accelerated by the instabilities.

[0052] The integrity of the combustion chamber is also ensured because, by carrying out combustions at high and low air-fuel ratios, the flame temperatures are lower than when combustion is carried out under stoichiometric conditions. Potential flame fronts originating from stoichiometric zones that might be present are not attached to the injector lips, which limits injector damage.

[0053] An example of an embodiment provides, for operation under typical conditions of a gas turbine of a turboprop, a rich zone richness of the order of 4 for the dihydrogen-air mixture injected by the internal channel 6, i.e. a richness well above the stoichiometric dosage of richness 1, and an air supply by means of the annular channel 8 in such quantity that the overall richness is fixed between 0.15 and 0.50 depending on the operating points of the turboprop.

[0054] Figure 4 shows various possible embodiments of the outlet of the internal channel 6 for premix injection. The shape and thickness of the outlet 16 of the internal channel, 16a, 16b, 16c, can be adjusted relative to the basic shape 16 of the internal channel shown in Figure 4(A). In Figure 4(B), the end 16a of the internal channel is formed with an inward bevel; in Figure 4(C), the end 16b is also beveled. In Figure 4(D), the end 16c of the internal channel is flared but has a terminal face perpendicular to the longitudinal axis of the channel. These different configurations allow for managing the attachment of the first flame front 30 to the lip 16 according to the configurations of the injection system.

[0055] In [Fig.4](E) a screw 17 is added in the internal channel 6 so as to homogenize the dihydrogen-air premix.

[0056] As regards the external channel 8, the latter can open from a wall 240 as shown in [Fig.5] and have different configurations of the channel outlet lip:

[0057] Straight outlet 24 in [Fig.5](A), flared conical inclined outlet 24a in [Fig.5](B) or conical closing outlet 24b as in [Fig.5](C). These different configurations allow adjustment of the exit velocity of the air surrounding the rich flame exiting the internal channel 6.

[0058] This disclosure therefore relates to a method for injecting premixed dihydrogen with air for an aeronautical gas turbine based on staged combustion, in which: a. Combustion of the high-rich dihydrogen-air premix takes place in a first region and generates a first flame front attached to the lips of the injector; b. Rapid mixing of the combustion products via air injection to be burned in a second region, generating a second stable flame front.

[0059] This process notably allows: a. To obtain aerodynamically stabilized flames over a wide operating range, b. To achieve combustion with very low nitrogen oxide emissions, c. To avoid the risk of a flashback from the second flame front, d. To reduce noise pollution related to hydrogen combustion, e. To guarantee the integrity and lifespan of the injector.

[0060] The method as defined in the claims is not limited to the above description and can in particular be applied to injection systems disposed in rear walls of combustion chambers or protruding from such walls.

Claims

Demands

1. Injection method, for an injection device in a combustion chamber (4, 4') of an aircraft turbomachine (1), said injection device comprising an internal channel (6) surrounded by an external annular channel (8), said channels opening into said combustion chamber (4, 4') of said gas turbine, characterized in that it comprises an injection of a dihydrogen-air mixture (12a) with a hydrogen content greater than the stoichiometric dosage into said internal channel (6) and an injection of air into said external annular channel (8), producing, after ignition of said mixture at the outlet of the internal channel, at the outlet of said internal channel (6), a first flame front (30) resulting from a rich combustion, external to said internal channel adhering to a lip at the outlet of the internal channel, said first flame front being surrounded by a second flame front (31) resulting from a lean combustion with the air exiting said external channel.

2. Injection method according to claim 1 wherein said dihydrogen-air mixture (12a) has a hydrogen content greater than 2.

3. Injection method according to claim 1 wherein said dihydrogen-air mixture (12a) has a hydrogen content greater than or equal to 4.

4. Injection method according to claim 1, 2 or 3 wherein an air flow in the external annular channel is chosen such that the overall richness at the outlet of the internal channel (6) and external annular channel (8) assembly is fixed between 0.15 and 0.5 depending on the operating points of the turbomachine.

5. An injection method according to any one of the preceding claims, wherein the injection of the dihydrogen / air mixture (12a) and the device are configured to create at the outlet of the internal channel (6) said first flame front (30) resulting from a rich combustion of said mixture and to hook it onto a lip (16) of the internal channel (6), after ignition of said mixture.

6. Injection method according to claim 5 wherein the hydrogen content of the mixture is chosen so that said rich combustion takes place with a flame front temperature below 1800 K.

7. An injection method according to claim 5 or 6, wherein the hydrogen content of the mixture is chosen so that the first flame front (30) is laminar and has a Lewis number greater than 1 limiting thermo-diffusive instabilities.

8. Injection method according to claim 5, 6 or 7 wherein the mixture burned in the first flame front generates residual gases burned in the second flame front (31) stabilized by the supply of air from the external annular channel.

9. Injection method according to claim 8 wherein the second flame front is maintained at a temperature below 1800K.

10. Injection method according to claim 8 or 9 wherein the air injected through the annular channel is rotated by an annular auger (28).

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