FR3139378A1 - DEVICE AND METHOD FOR INJECTING A HYDROGEN-AIR MIXTURE FOR A TURBOMACHINE BURNER - Google Patents

Abstract

Device for injecting a combustible mixture, for a combustion chamber (100) of an aircraft turbomachine turbine, which comprises around a longitudinal axis (X) a central tubular channel (1), a first annular channel (2 ) around said central channel and a second annular channel (3) around the first annular channel (2), said channels (1, 2, 3) opening into said combustion chamber at the level of a first lip (9) of said central channel , a second lip (10) of said first annular channel and one end (11) of the second annular channel, said first annular channel comprising, upstream of said second lip (10), a dihydrogen injection device ( 5, 6, 7) in said first annular channel (2) in a flow of air (8) moving along said longitudinal axis of said first annular channel so as to produce a dihydrogen-air mixture flowing towards said combustion chamber . Figure 1

Description

DEVICE AND METHOD FOR INJECTING HYDROGEN-AIR MIXTURE FOR TURBOMACHINE BURNER

The present disclosure relates to the field of injection devices and methods for supplying gas turbines such as aircraft turbomachines powered by dihydrogen and air. This includes in particular civil and military aeronautical applications: helicopters, VTOLs, drones, APUs, turbogenerators, fixed-wing aircraft for leisure, business or commercial aviation, turbojets or turboprops.

The propulsion sectors, and in particular the aeronautics sector, are facing major environmental challenges. The interest in using combustion using dihydrogen rather than kerosene is increasingly strong because this combustion of dihydrogen would avoid carbon pollutant emissions such as carbon dioxide, carbon monoxide, unburned hydrocarbons or even fine particles and smoke.

A principle of micro-mixture burners of air and dihydrogen is known. Burners made 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 production cost, a high pressure drop and are specific to a given combustion chamber architecture.

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

More generally, it is important to keep in mind that lean combustion fueling processes tend to generate significant thermo-acoustic instabilities that can damage these systems, while stable combustion is necessary to avoid affecting engine performance. Rich combustion fueling processes, on the other hand, tend to emit more pollutants than lean combustion processes if they are not sized correctly.

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

At equivalent thermodynamic conditions in pressure, temperature, richness, the adiabatic temperature of the flame of a hydrogen-air combustion is higher than the flame from a kerosene-air combustion.

Similarly, flame speeds 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 layers, and cause serious damage to these systems, or even cause safety problems.

The flammability limits of hydrogen, however, are wider than those of kerosene and allow a hydrogen-air mixture to be ignited at lower or higher richnesses than for kerosene, which can ultimately achieve lower flame temperatures than with kerosene.

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.

It is therefore sought to reduce combustion temperatures, reduce sound waves from combustion and limit the formation of nitrogen oxides to reduce both noise pollution and air pollution during turbine operation.

At the burner level, documents GB2502298A and US62675851 describe chamber geometries based on the principle of a micro-mix burner. This type of burner is designed to miniaturize the reaction zone by creating a multitude of micro-diffusion flames up to 4 cm long. The combustion process is based on an injection of hydrogen perpendicular to an air flow that carries the hydrogen (known as jet-in-crossflow). Once the rapid addition of hydrogen to the air has been achieved, the mixture is injected into the combustion chamber and is burned downstream of a multitude of injection holes. This technology reduces the risk of flashback because there is no premixing before injection. The operability of this type of injector may be limited, as may the thermal resistance of the wall containing the injection holes which is subjected to high temperature conditions.

In the context of burners using kerosene, the document “Advanced Combustor Systems for Stationary Gas Turbine Engines, Phase I. Review and Preliminary Evaluation, Volume I”, S.A. Mosier, R.M. Pierce, Contract 68-02-2136, FR-11405, Final Report, U.S. Environmental Protection Agency, 1980 proposes a geometry of the RQL type according to the acronym used in the field for “Rich Burn-Quick Mix-Lean Burn”.

This geometry aims to stage the richness in the kerosene combustion chamber in several zones: a first zone close to the injector outlet at a richness of approximately 1.8, followed by a second mixing zone with very intense air whose aim is to minimize the formation of stoichiometric regions and the formation of NOx and to complete the upstream rich combustion. Finally, in order to cool the combustion gases upstream of the DHP "High Pressure Distributor", additional air injections are planned in a third zone in order to make a second lean combustion at richness 0.5. Due to the specificity of hydrogen, the RQL type geometry optimized for kerosene combustion is no longer valid and must be redesigned.

Summary

The present disclosure relates to this end to a device for injecting a dihydrogen-air combustible mixture, for a combustion chamber of a turbomachine intended to stage the combustion to limit the generation of NOx and limit the noise emitted by the combustion. The present disclosure further relates to an associated injection method. More specifically, the present disclosure proposes a device for injecting a combustible mixture for a combustion chamber of an aircraft turbomachine turbine, which comprises, around a longitudinal axis, a tubular central channel, a first annular channel around said central channel and a second annular channel around the first annular channel, said channels opening into said combustion chamber at a first lip of said central channel, a second lip of said first annular channel and one end of the second annular channel, said first annular channel comprising, upstream of said second lip, means for injecting dihydrogen into said first annular channel in an air flow moving along said longitudinal axis of said first annular channel so as to produce a dihydrogen-air mixture flowing towards said combustion chamber.

The first lip may be arranged upstream of the end of the second annular channel, the central channel opening into the combustion chamber at the first lip upstream of the end of the second annular channel.

The second lip may be arranged upstream of the end of the second annular channel, the first annular channel opening into the combustion chamber at the second lip upstream of said end of the second annular channel.

The central channel can be equipped with a first spiral for rotating a gas passing through it.

The second annular channel can be provided with a second spiral for rotating a gas passing through it.

Said dihydrogen injection means advantageously comprise a plurality of first radial conduits between an external wall of said first annular channel and an annular tube supplying said conduits, said annular tube being supplied by one or more second dihydrogen supply conduits.

The present disclosure further relates to a method for supplying hydrogen-air combustion into a combustion chamber of an aircraft turbomachine turbine by means of an injection device as described above which comprises an injection of air into said chamber via said tubular central channel, an injection of dihydrogen and air into said chamber via the first annular channel to form a dihydrogen-air premix and an injection of air into said chamber via the second annular channel.

The dihydrogen-air premix is advantageously richer than two in dihydrogen.

The air injection into the central tubular channel and into the second annular channel is an injection of pure air so as to target an overall injection richness of between 0.3 and 0.5.

In the case where the device comprises a first spiral in the central tubular channel, the air is rotated in the central channel by said first spiral.

In case the device has a second spiral in the second annular channel, the air is rotated in the second annular channel.

The method is advantageously such that, after ignition, the injection of the rich hydrogen-air premix creates a first flame front resulting from the rich combustion of the hydrogen-air premix which clings to the lips of the central tubular channel and the first annular channel, this rich combustion with a richness greater than two being carried out with a flame front temperature of less than 1800 K.

As a result, the noise generated by the first flame front is reduced and the formation of nitrogen oxides is reduced.

Advantageously, the injection of air from the central tubular channel and the second annular channel dilutes and confines the burnt gases from the combustion of the rich hydrogen-oxygen premixture to form a lean mixture creating a second lean combustion flame front at a temperature below 1800K.

As a result, the noise generated by the second flame front is also reduced and the formation of nitrogen oxides is also reduced.

The creation of these two rich and lean flame fronts makes it possible to distribute the thermo-acoustic load resulting from combustion over a larger surface area, and therefore to reduce the noise pollution resulting from combustion.

Preferably, said second flame front is turbulent and is not attached to said lips.

Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the attached drawings, in which:

represents a schematic longitudinal sectional view of an injection device according to one embodiment;

represents a schematic cross-sectional view of means for supplying an annular channel according to a first embodiment;

represents the device of the with flame fronts;

represents a cross-section of a variant of means for supplying an annular channel according to a second embodiment;

represents a longitudinal section of the means of the .

represents a schematic longitudinal section view of an injection device according to another embodiment.

Description of embodiments

Reference is now made to the which represents a section of a combustible mixture injection device produced according to the principle of the present disclosure by a plane comprising a longitudinal axis X of the device.

The device comprises a central tubular channel 1 centered on the X axis, a first annular channel 2 around said central annular channel and a second annular channel 3 around the first annular channel 2.

Said channels 1, 2, 3 open into a combustion chamber 100. The central tubular channel comprises a first circular lip 9 surrounded by the first annular channel at an outlet plane 4 of said central channel, the first annular channel comprises a second circular lip 10 still at the outlet plane 4. The second circular lip is surrounded by the second annular channel and the first lip and second lip are set back by a height h relative to the plane of the outlet 11 of the second annular channel. Thus the outlets of the central tubular channel and of the first annular channel are upstream of the outlet of the second annular channel.

The first annular channel comprises, upstream of said second lip 10, a device for injecting dihydrogen into an air flow 8 moving along the longitudinal axis so as to produce a dihydrogen-air mixture flowing towards said combustion chamber. To inject the dihydrogen, the means comprise radial conduits 5 shown in section in which open into the external wall of the first annular channel 2. To clarify, the ratio of the distance from the outlet to the diameter of the first channel 2 can be between 1 and 10, more preferably between 1 and 5.

In , the dihydrogen injections are of the “jet-in-cross-flow” type, i.e. in French radial injections of dihydrogen in an axial jet of air, in order to obtain rapid premixing, over a minimized axial length, of the dihydrogen-air premix 15 exiting the first annular channel 2.

These radial conduits are supplied according to the example by an annular tube 6 itself supplied by one or more second conduits 7 for supplying dihydrogen from a pump or a pressure tank not shown. The number of first conduits is for example from 10 to 20 and for example of the order of 16 for a good distribution of the dihydrogen.

Alternatively, depending on the and the , respectively cross section and longitudinal section on one side of the axis X of the device, the dihydrogen injection means comprise first conduits 51 supplied by an annular tube 61 through sub-conduits 52 but the dihydrogen is mixed with air in hollow sectors 21 supplying the first annular channel from below, opposite the outlet of said channel in the combustion chamber. In this example, the conduits 51 each supply two sectors.

According to this example, four hollow sectors, each supplied by four first conduits 51 in which the dihydrogen-air mixture is made, are present under the first annular channel 2.

According to this embodiment, the injection process is improved by the addition of an air rotation device 8 (swirler in English), consisting of several hollow blades, four blades on the , in which the dihydrogen circulates. The latter is injected by jet-in-cross-flow injections 51 into the blades of the rotating device to optimize the mixing process.

The device of the present disclosure allows for staged combustion of hydrogen to bypass the nitrogen oxide formation zone via combustion of a rich hydrogen-air premix in a first zone, and combustion of residual gases in a lean second zone. The staged combustion concept allows for a wider range of injector operability than a lean combustion-oriented hydrogen injection strategy, where a lean premix is directly burned in the chamber and aims to reduce NOx formation.

The risk of flashback is limited with rich combustion because thermo-diffusive instabilities are not present on the first flame front. The flame speed is therefore not accelerated by the instabilities. In addition, the richness staging avoids the formation of a stoichiometric flame front because the hydrogen is either pre-mixed rich or vitiated by combustion gases. This has the effect of reducing the speed of the flame front, which is highly dependent on the composition of the gases to be burned.

The stabilization of two flame fronts 17 and 18, front 17 attached to the lips 9 and 10 of the injector for the rich flame and front 18 detached for the lean flame, makes it possible to divide the thermo-acoustic loads linked to combustion: the noise generated by combustion is distributed over two flame fronts, i.e. over a larger surface area than in the case where a single flame front is generated.

The integrity of the hearth is also ensured because by performing combustions at high and low richnesses, the flame temperatures are lower than when performing combustion under stoichiometric conditions. Potential flame fronts from stoichiometric zones that could be present in reality will not be attached to the injector lips, thus limiting damage to the injector.

By significantly increasing the surface area of the flame front via the injection of the rich hydrogen-air premix into the first annular channel 2, the length of the flame is reduced, which makes it possible to create combustion chambers with reduced bulk compared to injection into a central tubular channel.

With reference to Figures 3 and 4B, in order to promote the interaction between the air of the channel 16 and the premix flame 17, a withdrawal of the lip 10 relative to the end of the second annular channel is provided, withdrawal noted h on the to improve the interaction between the jet 16 exiting the second annular channel and the jet 15 exiting the first annular channel.

In the context of operation under typical turboprop conditions, the rich zone richness can notably be set around 4 and the overall richness set between 0.17 and 0.31 depending on the operating points of the turboprop.

The size of such a device for a combustion chamber of an aircraft turboprop turbine is of the order of 30 mm to 40 mm.

There represents a variant of the injection system applied to the entire bottom of the aeronautical combustion chamber with the shaft in the center where the central tubular channel 1a is made up of a third annular channel around the shaft 20, each of the channels being provided with a spiral 12, 13, 19, the annular flame fronts surrounding the shaft 20.

1. Une combustion du prémélange hydrogène-air à richesse élevée a lieu dans une première région qui génère un premier front de flamme annulaire accroché aux lèvres 9, 10 de l’injecteur, première lèvre 9 interne et deuxième lèvre 10 externe du canal annulaire d’injection du mélange dihydrogène-air;
2. Les produits de combustion sont ensuite mélangés rapidement via l’injection d’air centrale et périphérique pour être brulés dans une seconde région en générant un second front de flamme décroché.

The present disclosure thus relates to a tri-coaxial hydrogen injection system pre-mixed with air for an aeronautical or land-based gas turbine, based on staged combustion:

1. A combustion of the hydrogen-air premixture at high richness takes place in a first region which generates a first annular flame front attached to the lips 9, 10 of the injector, first internal lip 9 and second external lip 10 of the annular injection channel of the dihydrogen-air mixture;
2. The combustion products are then rapidly mixed via central and peripheral air injection to be burned in a second region generating a second detached flame front.

1. D’obtenir des flammes stabilisées aérodynamiquement sur une large plage de fonctionnement,
2. De réaliser une combustion à très faible émission d’oxydes d’azote,
3. D’éviter le risque de flashback du second front de flamme,
4. De diminuer les nuisances sonores liées à la combustion de l’hydrogène,
5. D’obtenir des flammes courtes avec une répartition des charges thermiques,
6. D’améliorer l’intégrité et la durée de vie de l’injecteur.

This system allows in particular:

1. To obtain aerodynamically stabilized flames over a wide operating range,
2. To achieve combustion with very low emissions of nitrogen oxides,
3. To avoid the risk of flashback from the second flame front,
4. To reduce noise pollution linked to the combustion of hydrogen,
5. To obtain short flames with a distribution of thermal loads,
6. To improve injector integrity and life.

The device of the invention is thus associated with a method for supplying hydrogen-air combustion in a combustion chamber of an aircraft turbomachine turbine which comprises an injection of air 14 into said chamber via said tubular central channel 1, an injection of dihydrogen 15a and air 8 into said chamber via the first annular channel 2 to form a dihydrogen-air premix 5 and an injection of air 16 into said chamber via the second annular channel 3.

The dihydrogen-air premix 15 can then have a richness greater than two in dihydrogen while the injection of air 14 into the central tubular channel 1 and into the second annular channel 3 is an injection of pure air calibrated so as to target an overall injection richness of between 0.3 and 0.5.

According to the example of the , the device comprising a first spiral 12 in the central tubular channel 1, the air 14 is rotated in this central channel 1 by this first spiral while the device comprising a second spiral 13 in the second annular channel, the air 4 is rotated in the second annular channel.

After ignition, the injection of the rich hydrogen-air premix 15 creates a first flame front 17, this flame coming from the rich combustion of the hydrogen-air premix which clings to the lips 9 and 10 of the central tubular channel 1 and the first annular channel 2.

This rich combustion with a richness greater than two is carried out with a flame front temperature of less than 1800 K, limiting NOx emissions. The injection of air from the tubular central channel 1 and from the second annular channel 3 dilutes and confines the burnt gases from the combustion of the rich hydrogen-oxygen premix to form a lean mixture creating a second lean combustion flame front 18 at a temperature of less than 1800 K, also limiting NOx emissions. This second flame front 18, which is also turbulent, is not attached to said lips 9, 10 of the tubular central channel 1 and the first annular channel 2.

The device and method of the present disclosure perform well while limiting NOx emissions.

The invention which is the subject of the following claims is not limited to the preceding description and in particular the shape of the lips and the outlet of the second annular channel can be of various shapes such as straight, flared, beveled, narrowed and of various thicknesses.

Claims (10)

Device for injecting a combustible air-dihydrogen mixture, for a combustion chamber (100) of an aircraft turbomachine turbine, characterized in that it comprises around a longitudinal axis (X) a tubular central channel (1), a first annular channel (2) around said central channel and a second annular channel (3) around the first annular channel (2), said channels (1, 2, 3) opening into said combustion chamber at a first lip (9) of said central channel, a second lip (10) of said first annular channel and an end (11) of the second annular channel, said first annular channel comprising, upstream of said second lip (10), a device for injecting dihydrogen (5, 6, 7) into said first annular channel (2) in an air flow (8) moving along said longitudinal axis of said first annular channel so as to produce a dihydrogen-air mixture flowing towards said combustion chamber. Injection device according to claim 1, for which the first lip (9) is arranged upstream of the end of the second annular channel, the central channel (1) opening into the combustion chamber (100) at the level of the first lip (9) upstream of the end (11) of the second annular channel and/or for which the second lip (10) is arranged upstream of the end of the second annular channel, the first annular channel opening into the combustion chamber at the level of the second lip (10) upstream of said end (11) of the second annular channel. Injection device according to claim 1 or 2, for which the central channel (1) is provided with a first spiral (12) for rotating a gas passing through it. Injection device according to any one of the preceding claims, for which the second annular channel (3) is provided with a second spiral (13) for rotating the gas passing through it. Injection device according to any one of the preceding claims, for which said dihydrogen injection means (5, 6, 7) comprise a plurality of first conduits (5, 51) between an external wall of said first annular channel (2) and an annular tube (6, 61) for supplying said conduits, said annular tube being supplied by one or more second conduits (7) for supplying dihydrogen. Method for supplying hydrogen-air combustion into a combustion chamber of an aircraft turbomachine turbine by means of an injection device according to any one of the preceding claims, characterized in that it comprises an injection of air (14) into said chamber via said tubular central channel (1), an injection of dihydrogen (15a) and air (8) into said chamber via the first annular channel (2) to form a dihydrogen-air premix (15) and an injection of air (16) into said chamber via the second annular channel (3). Method for supplying a hydrogen-air combustion according to claim 6 for which the dihydrogen-air premix (15) has a richness greater than two in dihydrogen. Method for supplying a hydrogen-air combustion according to claim 7, for which the injection of air (14) into the central tubular channel (1) and into the second annular channel (3) is an injection of pure air so as to target an overall injection richness of between 0.3 and 0.5. A method of supplying a hydrogen-air combustion according to any one of claims 6 to 8, for which the device comprising a first spiral (12) in the tubular central channel, the air (14) is rotated in the central channel (1) by said first spiral and/or for which the device comprising a second spiral (13) in the second annular channel, the air (4) is rotated in the second annular channel. A method of supplying a hydrogen-air combustion according to any one of claims 6 to 9, for which after ignition, the injection of the rich hydrogen-air premix (15) creates a first flame front (17) resulting from the rich combustion of the hydrogen-air premix which clings to the lips (9, 10) of the tubular central channel (1) and the first annular channel (2), this rich combustion with a richness greater than two being carried out with a flame front temperature of less than 1800 K and for which the injection of air from the tubular central channel (1) and the second annular channel (3) dilutes and confines the burnt gases resulting from the combustion of the rich hydrogen-oxygen premix to form a lean mixture creating a second flame front (18) of lean combustion at a temperature of less than 1800 K, said second flame front (18) being turbulent and not being attached to said lips (9, 10).