Patent Application
20240328617
The present document relates to turbomachines whose combustion chamber is supplied by separate injections of dihydrogen and air.
The aeronautics sector is facing major environmental challenges. The interest in making use of combustion using dihydrogen instead of using kerosene is greater and greater because this combustion of dihydrogen serves to avoid emissions of carbon dioxide (CO2) and carbon pollutants such as carbon monoxide, unburned hydrocarbons or even fine and smoke particles.
A principle of burners micro-mixing air and dihydrogen is known. However, such burners do not guarantee the thermal strength of a pierced wall or that there are no flashbacks in the dihydrogen injection device. The geometrical system of these burners is also complex. Such burners have a high implementation cost, a large loss of load and these burners are specific to a given combustion chamber architecture.
In fact, dihydrogen combustion leads to various problems. Thus, risks of flashbacks in the injection device may happen for systems operating with mixtures of dihydrogen and air. This may damage the combustion chamber and pose serious safety problems. Finally, combustion of dihydrogen generates high thermal loads on the walls of this combustion chamber which tends to reduce the lifetime. High gas temperatures and emissions of nitrogen oxides are produced. These gas temperatures and emissions of nitrogen oxides are greater than those produced by kerosene flames at equivalent richness. This is, as a matter of fact, hardly compatible with current standards.
The present document relates to a longitudinal-axis dihydrogen injection device intended to be mounted on an annular bottom of an annular combustion chamber of a turbomachine comprising an inner channel for dihydrogen circulation and an outer annular channel for circulation of a mixture comprising at least air, where the inner channel and the outer annular channel are coaxial, an inner swirler is housed in the inner channel and an outer swirler is housed in the outer annular channel and wherein a downstream end of the inner channel is arranged upstream, at a distance r, from a downstream end of the outer annular channel.
This device serves to produce a dihydrogen/air flame which can be used in turbomachines which serves both to produce low levels of emissions of nitrogen oxides, a reduced thermal load on the combustion chambers and the injector, and also to eliminate the risks of flame flashback. Additionally, this injector has the specific feature of being both simple to produce and easy to adapt to existing turbomachines operating with kerosene.
In general, a swirler serves to rotate a flow. Incorporating an inner swirler in the inner channel serves to create a recirculation zone in a dihydrogen flow passing through the inner channel and avoiding the combustion of the air and dihydrogen mixture from stabilizing on the downstream end of the inner channel. Recirculation zone is understood to mean a zone generating a centrifugal force with a low pressure inside configured to produce an axial velocity component in the flow on average negative compared to a main direction of the flow. This recirculation zone is similar to the one generated inside a vortex in which the air is aspirated. The inner recirculation zone blocks a portion of the dihydrogen flow along the longitudinal axis of the inner channel generating, in an outlet section of this inner channel, significant excess velocities near the walls of the inner channel compared with a flow with a uniform axial discharge velocity. Rotating the dihydrogen in the inner channel serves to avoid catching the flame on the downstream ends of the inner channel by aerodynamically stabilizing it above the inner channel. Because the downstream end of the inner channel is arranged a distance r upstream, that avoids the flame catching on the lips of the inner channel even more. Rotating the dihydrogen from the inner channel avoids placement of a complex cooling device for the dihydrogen injection device. In that way, the cost and weight of the dihydrogen injection device are improved. This dihydrogen injection device produces limited losses of load compared to other liquid injection devices using kerosene, as in the prior art. This dihydrogen injection device has a simple geometry, a low implementation cost.
This remote stabilization of the flames makes it easier to partially mix the mixture containing at least air with the dihydrogen leaving the inner channel, upstream from the flame, and avoids any risk of flashback. This makes it possible to overcome a combustion lean in dihydrogen in the combustion chamber. This device thus tends to greatly reduce the combustion temperatures and the emitted nitrogen oxides. This guarantees integrity of a combustion site.
The positioning of the downstream end of the inner channel upstream from the downstream end of the outer annular channel, at a distance referenced r on
The inner channel may be a central tubular channel.
At least the inner swirler of the inner channel may have a helical shape.
This helical shape serves to improve the aerodynamics of the dihydrogen flow passing through the inner swirler.
The inner swirler may be arranged along the longitudinal axis downstream from the outer swirler.
A rotation rate S generated by the inner swirler of the inner channel, defined as a ratio between a tangential velocity and the discharge velocity along the longitudinal axis of a flow of dihydrogen leaving the inner swirler, maybe greater than or equal to 0.6.
These values of the rotation rate S, which is a dimensionless number, serve to obtain flames rotating relative to the longitudinal axis which are freed from the inner channel.
The inner swirler of the inner channel may be arranged upstream, at a distance l, from the downstream end of the inner channel.
The inner channel may have an inner diameter d and the outer annular channel may have an inner diameter D such that the ratio D/d is included between 3 and 10.
This optimized ratio D/d allows operation in a lean dihydrogen regime.
A thickness of the wall of the inner channel e is such that the ratio e/d may be included between 0.05 and 0.7.
A ratio l/d may be included between 1 and 3.
The minimum distance lmin is equal to 1d such that a central recirculation zone enters into the inner channel. The selected range for l/d serves to get a good compromise and a rotation rate S sufficient for properly rotating the flame.
The distance r may be included between 0.05D and 0.5D.
There is an optimal value for the distance r which depends on the diameter D of the outer channel. If this distance r is too long, the recirculation zone becomes unstable. The value range selected for r is optimized in order to get a stable recirculation zone.
This distance r compared to the downstream end of the outer annular channel serves to increase the operating domain where the flame is detached by moving back a dihydrogen introduction zone relative to the aerodynamic stabilization zone of the flame.
The outer swirler of the outer annual channel may be arranged near an upstream end of the outer annular channel, at a distance L from the downstream end of the outer annular channel.
The distance L may be included between 1D and 5D.
The rotation rate S may be greater than 0.6; where a dihydrogen discharge velocity ui in the inner channel is greater than a critical value ui.c. and satisfies the following relationship:
where:
This critical value ui,c serves to assure that the flame formed on outlet from the injection device is detached from the downstream ends of the inner channel for a broad range of engine operation.
The mixture may be air.
The present document relates to an assembly comprising the device of the aforementioned type, wherein the inner channel, fluidly connected to dihydrogen supply means, comprises the inner swirler configured for rotating the dihydrogen, and the outer annular channel, fluidly connects air supply means, comprises the outer swirler configured for rotating the air.
Other characteristics details and advantages will appear upon reading the following detailed description, and analyzing the attached drawings, on which:
The present document relates to a dihydrogen injection device 2 intended to be mounted on an annular bottom of an annular combustion chamber 4 of a turbomachine. This dihydrogen injection device 2 is used in a lean dihydrogen combustion configuration such that the flame temperatures and the formation of nitrogen oxides are reduced. It is said that the injection device is lean when the dioxygen is in excess compared to a stoichiometric combustion of dihydrogen and air, and that the injection system is rich when there is an excess of dihydrogen compared to this stoichiometric combustion. Stoichiometric combustion is defined as that for which the right number of hydrogen and oxygen atoms are present for consuming all of the combustible and that there is only water in the combustion products. The present disclosure is situated is in the context of lean dihydrogen combustion.
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A first gas is injected from an inlet 10 located at one upstream end of the inner channel 6. This first gas is dihydrogen 12. The inner channel 6 comprises an inner diameter d. The choice of the inner diameter d of the channel depends on a desired thermal power. A thickness of a wall of the inner channel e corresponds to half of the difference of an outer diameter of the inner channel and an inner diameter of the inner channel d. A ratio l/d may be included between 0.05 and 0.7.
This inner channel 6 comprises an inner swirler 14 configured for rotating a dihydrogen flow 12 around a longitudinal axis X. The inner swirler 14 of the inner channel 6 is arranged upstream, at a distance/from a downstream end 16 of the inner channel. The distance i between the downstream end 16 of the inner channel 6 and a downstream end 18 of the inner swirler 14 is included between 1d and 5d. As shown in
The inner swirler 14 may, for example, comprise a helical part more with a suitable helical pitch. This helical pitch is configured for defining a positioning of the flame 22 at the outlet of the injection device 2 in order to minimize polluting emissions and define a heat transfer of the injection device. This helical part rotates the dihydrogen flow with a rotation rate characterized by a dimensionless number S. This rotation rate S is defined as a ratio of a kinetic moment referred to the product of a radius of the channel multiplied by an impulse from the rotated dihydrogen flow 12, according to the following formula:
where Gθ is the kinetic moment of the flow along an axial direction, Gz is the impulse of the flow along the axial direction and d is the diameter of the channel. In general, approximate expressions are used for estimating Gθ and Gz based on the tangential and axial velocities of the flow rotated in the channel. In this case S corresponds to the ratio of a tangential velocity divided by an axial velocity. The tangential velocity corresponds to a rotational component of the velocity relative to the axis of injection.
A blockage rate of the dihydrogen flow 12 in the inner channel 6 is established so as to be sufficiently high for pushing back the flame 22 forming at a downstream end 24 of the outer annular channel 8. The blockage rate represents the ratio between a section occupied by the recirculation zone 20 pushing back inside the dihydrogen injection device 12 near the downstream end 16 of the inner channel 6 relative to a passage section of the inner channel 6. This blockage rate depends on the shape of the recirculation zone 20. More precisely, it is an aerodynamic element which depends on the dimensional parameters of the dihydrogen injection device 2. The higher a l/d ratio, the greater is the distance of depression of the inner swirler 14 relative to the diameter and the higher a value for the rotation rate S can be chosen by modifying the geometry of the inner swirler 14. The rotation rate S is at least equal to 0.6 and a ratio l/d is included between 1 and 3. As shown in
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The outer annular channel 8 is configured for receiving a second gas comprising air or a mixture of air and dihydrogen. This gas enters the outer annular channel via an inlet 26 arranged upstream from the outer annular channel.
A section ratio between the inner diameter d of the inner channel 6 and the inner diameter D of the outer annular channel 8 depends on:
An outer swirler 28 is housed at an upstream end 30 of the outer annular channel 8. This outer swirler 28 is annular. This outer swirler 28 may be radial. This annular outer swirler 28 is arranged in the distance L from the downstream end 36 of the outer annular channel 8. This distance L is included between 1D and 5D. The combustible is then rotated at the center by the inner swirler 14 whereas the air with a mixture containing at least air is rotated around by the outer swirler 28. This generates a whirling assembly.
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In order to generate rotational movement of the flames, several conditions are necessary.
The rotation rate S must be high in the inner channel 6. This rotation rate S is over 0.6. In fact, below 0.6, a recirculation zone with a sufficiently low pressure at the center does not form because the tangential velocity of the dihydrogen flow is not sufficient.
The outer swirler 28 also participates in maintaining the recirculation zone. The dimensionless number associated with the rotation rate generated by the outer swirler 28 is denoted by Sext. Sext is greater than 0.6. Sext is defined analogously to S; meaning that it involves a ratio of the tangential velocity to an axial discharge velocity of the airflow.
Stabilization of the flame, free or caught to the downstream end 16 of the inner channel 6, depends on a stretching of a shearing layer upstream from the downstream end of the inner channel on which the flame could catch. In order to aerodynamically stabilize of flame away from the downstream end of the inner channel, it is necessary to sufficiently stretch a base of the flame for the purpose of locally extinguishing it and stabilizing it away from the downstream end of the inner channel. The main parameters controlling a local stretching value are the rotation rate of the dihydrogen flow characterized by the dimensionless number S, the distance r and a discharge velocity ui of the dihydrogen in the inner channel.
For a swirler characterized by a rotation rate S greater than 0.6, a discharge velocity ui of the dihydrogen in the inner channel must be greater than a critical value ui.c. and satisfy the following relationship:
where:
There is an optimal value for the distance r which depends on the inner diameter D of the outer annular channel. If the distance r is too long, the recirculation zone 20 becomes unstable. Under such conditions, the distance r must be included between 0.05D and 0.5D.
As a function of the distance r, the mixing is going to be done more or less early inside the dihydrogen and air injection device 2, and if that occurs too early, the flame 22 may flash back inside the outer annular channel 8 between the downstream end 16 of the inner channel and the downstream end 24 of the outer annular channel, which is very damaging to the device and to the bottom of the combustion chamber 4. Rotation of the flame 22 is therefore configured in order to avoid the flame 22 flashing back into the dihydrogen injection device 2. The parameters to be controlled are therefore at once the rotation rate S of the flow in the inner channel, the rotation rate Sext, and the distance r.
In the context of the present document, the swirlers 14, 28 serve to rotate a first flow relative to a second flow. Incorporating the inner swirler 14 in the inner channel 6 serves to create a recirculation zone 20 in a dihydrogen flow passing through the inner channel 6 and avoiding the flame stabilizing on the downstream end of the inner channel. The inner swirler 14 of the inner channel 6 rotates the dihydrogen flow 2 sufficiently for creating a recirculation zone entering the inside of the inner channel 6 which blocks a part of the dihydrogen flow along the longitudinal axis x of the inner channel 6 generating significant excess velocities compared to the axial discharge velocity near the walls of the inner channel 6. Rotating the dihydrogen in the inner channel 6 serves to avoid catching the flame 22 on the downstream ends of the outer annular channel 8 by aerodynamically stabilizing it above the inner channel 6. Rotating the dihydrogen from the inner channel 6 avoids placement of a complex cooling device for the dihydrogen injection device 2.
This remote stabilization of the flame 22 is made easier by the partial mixing of the air with the dihydrogen inside the outer channel 8 above the downstream end 16 of the inner channel, upstream from the flame 22, and by avoiding any risk of flashback of the flame 22 in the inner channel 6 and in the outer annular channel 8 upstream from the downstream end 16 of the inner channel 6. This makes it possible to overcome a combustion lean in dihydrogen in the combustion chamber. This device thus tends to greatly reduce the combustion temperatures and the emitted nitrogen oxides. This also guarantees integrity of a combustion site.
The positioning of the downstream end 16 of the inner channel 6 upstream from the downstream end 24 of the outer annular channel 8 serves to optimize the mixture of the dihydrogen and the air. That increases the domain of operation where the flame 22 is detached by drawing back the zone of introduction of dihydrogen relative to the aerodynamic stabilization zone of the flame.
The optimization done with this injector and with the architecture thereof is specifically directed towards dihydrogen combustion. Since the dihydrogen burns much faster than any other combustible and in particular kerosene, the rotation speeds of the injection device 2 bringing the combustible and that bringing the air are not in the same order of magnitude as those used for kerosene. Since kerosene is liquid, passage sections for such kerosene injection devices are very small. At the outlet of the kerosene injection device, an outlet channel is of order a millimeter or less than a millimeter. There, where in the present document, the order of magnitude is several tens of millimeters. The operation is therefore very different for a gaseous combustible such as dihydrogen.
The injection device is advantageously implemented within an assembly comprising the injection device, wherein the inner channel is fluidly connected to dihydrogen supply means and the outer annular channel is fluidly connected to air supply means.
The dihydrogen supply means are in particular suited for delivering a dihydrogen gas flow without diluting gas, meaning a flow comprising at least 90% dihydrogen by mass and in particular at least 95% dihydrogen by mass, and advantageously at least 99% dihydrogen. The dihydrogen supply means comprise for example at least one pressurized tank provided with at least one valve, and/or at least one device for chemical generation of dihydrogen gas.
The air supply means are in particular suited for delivering an airflow without addition of diluting gas. The air supply means comprise for example an atmospheric air inlet from upstream of the turbomachine. This air is compressed before entering the annular combustion chamber. The air supply means may also comprise a source of dioxygen for enriching the airflow with dioxygen. The source of dioxygen may comprise a pressurized dioxygen tank provided with a valve and/or means for chemical generation of dioxygen gas.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2110692 | Oct 2021 | FR | national |
| FR2111267 | Oct 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2022/051883 | 10/5/2022 | WO |
