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 A HYDROGEN-AIR MIXTURE FOR A 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, VTOL, drones, APUs, turbogenerators, fixed-wing aircraft for leisure, business or commercial aviation, turbojets or turboprops.

The propulsion sectors and in particular the aeronautics sector face major environmental challenges. The interest in using combustion using dihydrogen rather than using kerosene is increasingly strong because this combustion of dihydrogen would make it possible to avoid carbon polluting emissions such as carbon dioxide, monoxide carbon, unburned hydrocarbons or even fine and smoked particles.

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 loss and are specific to a given combustion chamber architecture.

In terms 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.

More generally, it is important to keep in mind that lean combustion power processes tend to generate significant thermo-acoustic instabilities that can damage these systems whereas stable combustion is necessary to avoid altering the engine performance. Rich combustion feed 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 take into consideration in the combustion chamber:

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

Likewise, flame speeds from hydrogen-air combustion are greater 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 are, however, wider than those of kerosene and allow a hydrogen-air mixture to be ignited at lower or higher levels than for kerosene, which can ultimately reach temperatures flames lower than with the use of 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.

In terms of burners, documents GB2502298A and US62675851 describe chamber geometries based on the principle of a micro-mix burner (also known as micro-mix). This type of burner is designed to miniaturize the reaction zone by creating a multitude of diffusion micro-flames up to 4 cm long. The combustion process is based on an injection of hydrogen perpendicular to a flow of air which 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 can be limited, as can the thermal resistance of the wall containing the injection holes which is subject 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 an RQL type geometry according to the acronym used in the field for “Rich Burn-Quick Mix-Lean Burn in English” or rich combustion-rapid mixture-lean combustion in French.

This geometry aims to spread the richness in the kerosene combustion chamber into several zones: a first zone close to the outlet of the injectors 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 rich upstream combustion. Ultimately, in order to cool the combustion gases upstream of the DHP “High Pressure Distributor”, additional injections of air are planned in a third zone in order to produce a second lean combustion at 0.5 richness. Due to the specificity of hydrogen, the RQL type geometry optimized for kerosene combustion is no longer valid and must be rethought.

Summary

To this end, the present disclosure concerns a device for injecting a dihydrogen-air fuel mixture, for the combustion chamber of a turbomachine intended to stage combustion to limit the generation of NOx and limit the noise emitted by combustion. The present disclosure further relates to an associated injection method. More precisely, the present disclosure proposes a device for injecting a combustible mixture for the combustion chamber of an aircraft turbomachine turbine, which comprises, around a longitudinal axis, a central tubular channel, a first annular channel around said channel central and a second annular channel around the first annular channel, said channels opening into said combustion chamber at the level of 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 a flow of air 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 can be arranged upstream of the end of the second annular channel, the central channel opening into the combustion chamber at the level of the first lip upstream of the end of the second annular channel.

The second lip can be 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 upstream of said end of the second annular channel.

The central channel may be provided with a first spindle for rotating a gas passing through it.

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

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

The present disclosure further relates to a method of supplying a hydrogen-air combustion in 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 through said central tubular channel, an injection of dihydrogen and air into said chamber through the first annular channel to form a dihydrogen-air premix and an injection of air into said chamber through the second annular channel.

The dihydrogen-air premix advantageously has a richness greater than two in dihydrogen.

The injection of air 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 includes a first twist in the central tubular channel, the air is rotated in the central channel by said first twist.

In the case where the device includes a second twist in the second annular channel, the air is rotated in the second annular channel.

The process 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 taking place with a flame front temperature lower 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 resulting from the combustion of the rich hydrogen-oxygen premix 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 characteristics, details and advantages will appear on reading the detailed description below, and on analyzing 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 sectional 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 axis X, 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 always at the level of 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 channel annular. Thus the outlets of the central tubular channel and 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 chamber combustion. 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 ideas, the ratio of the distance relative to the outlet to the diameter of the first channel 2 can be between 1 and 10, more preferentially between 1 and 5.

In , the injections of dihydrogen are of the "jet-in-cross-flow" type, that is to say in French radial injections of dihydrogen in an axial jet of air, in order to obtain a rapid premix, over a minimized axial length , of the dihydrogen-air premix 15 leaving 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 10 to 20 and for example around 16 for good distribution of the dihydrogen.

Alternatively, depending on the and the , respectively cross section and longitudinal section on one side of the axis air in hollow sectors 21 supplying the first annular channel from below, opposite the outlet of said channel into 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 takes place are present under the first annular channel 2.

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

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

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 thus not accelerated by instabilities. In addition, the wealth 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 strongly 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: noise generated by the combustion is distributed over two flame fronts, that is to say 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 carrying out combustion at high and low levels, the flame temperatures are lower than by carrying out combustion under stoichiometric conditions. Potential flame fronts from stoichiometric zones that could be present in reality will not be attached to the lips of the injector, thus limiting damage to the injector.

By significantly increasing the surface of the flame front via the injection of the rich hydrogen-air premix in the first annular channel 2, the length of the flame is reduced which makes it possible to produce combustion chambers with a reduced footprint compared to a 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 is provided relative to the end of the second annular channel, withdrawal noted h on the to improve the interaction between the jet 16 leaving the second annular channel and the jet 15 leaving the first annular channel.

In the context of operation under typical conditions of a turboprop, the rich zone richness can in particular be set around 4 and the overall richness fixed 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 channels being provided with a tendril 12, 13, 19, the flame fronts of annular shape 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 concerns a tri-coaxial hydrogen injection system pre-mixed with air for an aeronautical or terrestrial gas turbine, based on staged combustion:

1. Combustion of the hydrogen-air premix 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 dihydrogen-air mixture;
2. The combustion products are then mixed rapidly via central and peripheral air injection to be burned in a second region by generating a second stalled 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 nitrogen oxide emissions,
3. To avoid the risk of flashback of 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 the integrity and lifespan of the injector.

The device of the invention is thus associated with a method of 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 channel central tubular 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 be richer than two in dihydrogen while the injection of air 14 in the central tubular channel 1 and in 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 twist 12 in the central tubular channel 1, the air 14 is rotated in this central channel 1 by this first twist while the device comprising a second twist 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 takes place with a flame front temperature below 1800 K, limiting NOx emissions. The injection of air from the central tubular channel 1 and from 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 below 1800K, again limiting NOx emissions. This second flame front 18 which is also turbulent is not attached to said lips 9, 10 of the central tubular channel 1 and the first annular channel 2.

The device and method of the present disclosure are efficient while limiting NOx emissions.

The invention which is the subject of the claims which follow is not limited to the description which precedes 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, tightened and of thickness various.

Claims (10)

Device for injecting a dihydrogen air fuel mixture, for a combustion chamber (100) of an aircraft turbomachine turbine, characterized in that it 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 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 device for injecting dihydrogen (5, 6, 7) into 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. 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 chamber of combustion 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 spinner (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 spinner (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 in 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 a injection of air (14) into said chamber through said central tubular channel (1), an injection of dihydrogen (15a) and air (8) into said chamber through the first annular channel (2) to form a dihydrogen-premixture air (15) and an injection of air (16) into said chamber via the second annular channel (3). A method of supplying hydrogen-air combustion according to claim 6 for which the dihydrogen-air premix (15) has a dihydrogen content greater than two. Method for supplying hydrogen-air combustion according to claim 7 for which the injection of air (14) in the central tubular channel (1) and in 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. Method of supplying hydrogen-air combustion according to any one of claims 6 to 8 for which the device comprising a first swirl (12) in the central tubular channel, the air (14) is rotated in the central channel (1) by said first twist and/or for which the device comprising a second twist (13) in the second annular channel, the air (4) is rotated in the second annular channel. Method for supplying 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) coming from the rich combustion of the hydrogen-air premix which clings to the lips (9, 10) of the central tubular channel (1) and the first annular channel (2) this rich combustion of richness greater than two taking place with a temperature of flame front less than 1800 K and for which the injection of air from the central tubular 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 below 1800K, said second flame front (18) being turbulent and not being attached to said lips (9, 10).