Method for injecting hydrogen-air mixture for turbine engine combustor

Abstract

The invention relates to an injection method for an injection device in a combustion chamber of an aircraft turbine engine, said injection device comprising an inner channel (6) surrounded by an outer annular channel (8), said channel opening into said combustion chamber (4, 4 ') of a gas turbine, characterized in that the inner channel (6) is surrounded by an outer annular channel (8). The injection method comprises injecting a gaseous hydrogen-air mixture (12a) having a hydrogen richness level greater than a stoichiometric amount into the inner channel (6), and injecting air into the outer annular channel (8) so as to produce a first flame front (30) produced by rich combustion at the outlet of the inner channel (6), the first flame front is surrounded by a second flame front (31) produced by lean combustion.

Description

Technical Field

[0001] The present disclosure relates to the field of methods for supplying fuel to injection devices for gas turbines, such as aircraft turbine engines powered by gaseous hydrogen and air. This encompasses civil and military aviation applications: helicopters, VTOL, drones, APUs, turbogenerators, fixed-wing aircraft for leisure, business or commercial use, turbojets or turboprops. Background Art

[0002] The field of propulsion, and in particular aviation, is facing major environmental challenges. There is an increasing interest in using combustion based on gaseous hydrogen instead of kerosene, since burning gaseous hydrogen will avoid the emission of carbon pollutants such as carbon dioxide, carbon monoxide, unburned hydrocarbons or fine particles and smoke.

[0003] The principle of burners is known, in which air and gaseous hydrogen are slightly mixed. Burners implemented according to this principle cannot guarantee the absence of flashback in the gaseous hydrogen injection device and have complex geometries. Such burners have high production costs, high pressure losses, and they are specific to a given combustion chamber architecture.

[0004] There are two main technical configurations for hydrogen-air injection systems applied to gas turbines, namely lean injection systems and rich injection systems, with respect to injection and combustion.

[0005] More generally, it is important to remember that fueling methods involving lean combustion tend to produce significant thermoacoustic instabilities that can damage these systems, while stable combustion is necessary to avoid altering engine performance. On the other hand, fueling methods involving rich combustion tend to emit more pollutants than lean combustion methods if they are not properly designed.

[0006] Technical issues

[0007] The use of hydrogen involves several issues to consider in the combustion chamber:

[0008] Under the same thermodynamic conditions of pressure, temperature and richness, the adiabatic temperature of a hydrogen-air combustion flame is higher than that of a kerosene-air combustion flame.

[0009] Similarly, the flame speed of hydrogen-air combustion is higher than that of kerosene-air flames. High flame speeds may lead to flashback problems in injection systems, especially at the boundary layer, and may cause severe damage to these systems or may even cause safety issues.

[0010] However, the flammability range of hydrogen is wider than that of kerosene and allows hydrogen-air mixtures to ignite at lower or higher richness levels than kerosene, which ultimately can allow lower flame temperatures to be achieved than with kerosene.

[0011] Finally, the combustion of hydrogen with air tends to emit more noise than conventional kerosene combustion and thus can generate significant noise pollution at airports. Summary of the invention

[0012] A method for injecting a rich premixture dedicated to the combustion of gaseous hydrogen and air is proposed herein, which method allows solving the above-mentioned technical problem.

[0013] More specifically, the present disclosure proposes an injection method for an injection device in a combustion chamber of an aircraft turbine engine, the injection device comprising an inner passage surrounded by an outer annular passage, the passage leading to the combustion chamber of a gas turbine, the method comprising injecting a gaseous hydrogen-air mixture having a hydrogen richness level greater than the stoichiometric amount into the inner passage, and injecting air into the outer annular passage so as to generate a first flame front produced by rich combustion at the outlet of the inner passage after igniting the mixture, the first flame front being surrounded by a second flame front produced by lean combustion.

[0014] The method of operating the turbine with injection continuously after ignition allows the temperature of the flame front to be reduced, which reduces the NOx content of the combusted gases and reduces injector wear.

[0015] The features set out in the following paragraphs correspond to embodiments which can be implemented independently of one another or in combination with one another where appropriate:

[0016] The gaseous hydrogen-air mixture may have a hydrogen richness level greater than 2.

[0017] Advantageously, the gaseous hydrogen-air mixture may have a hydrogen richness level greater than or equal to 4.

[0018] The air flow rate in the outer annular channel may be chosen such that the overall richness level at the outlet of the inner channel / outer annular channel assembly is set between 0.15 and 0.5, depending on the operating point of the turbine engine.

[0019] The injection and injection means of the gaseous hydrogen-air mixture may be configured to produce said first flame front resulting from rich combustion of said mixture at the outlet of the inner passage and attach it to the peripheral lip of the inner passage.

[0020] The hydrogen richness of the mixture can be chosen so that the rich combustion takes place with a flame front temperature below 1800 K, which protects the combustion chamber.

[0021] The hydrogen richness of the mixture can be chosen so that the first flame front is laminar and has a Lewis number greater than 1, thereby limiting diffusion-thermal instabilities and thus avoiding flashback phenomena.

[0022] The mixture burning in the first flame front generates residual gases which are advantageously burned in a second flame front which is stabilized by supplying air from an outer annular channel.

[0023] The abundance of the second flame front allows the second flame front to be maintained at a temperature below 1800K.

[0024] The air ejected from the annular passage may be swirled by the annular swirler to make the second flame front turbulent and to prevent the second flame front from attaching to the lip of the inner passage.

[0025] Advantageously, positioning the downstream end of the inner channel upstream of the downstream end of the outer annular channel allows optimizing the mixing between the gases coming from the first combustion and the air injected by the outer channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, details and advantages of the present invention will become apparent upon reading the following detailed description of certain non-limiting exemplary embodiments and upon analyzing the accompanying drawings, in which:

[0027] [ Figure 1 ] shows a turbine engine comprising injection means arranged in the annular bottom of an annular combustion chamber according to three configurations;

[0028] [ Figure 2 ] shows a first schematic example in a cross-sectional side view of an injection device to which the method of the present disclosure is applied;

[0029] [ Figure 3 ] shows Figure 2 Schematic diagram of the device under combustion conditions;

[0030] [ Figure 4 ] shows multiple possible configurations of the internal channels of a device to which the method of the present disclosure is applied (Figures A, B, C, D, E);

[0031] [ Figure 5 ] show several exemplary configurations of annular channel outlets (Figures A, B, C) of an apparatus to which the method of the present disclosure is applied. DETAILED DESCRIPTION

[0032] The following drawings and description contain elements that may not only serve to provide a better understanding of the invention but may also contribute to its definition where appropriate.

[0033] Reference now Figure 1 , Figure 1 Three exemplary configurations are shown for mounting the injection device 2 on the turbine engine 1 depending on the orientation of the annular bottom of the annular combustion chamber 4, 4', 4" of the turbine engine: the combustion chamber 4" is oriented essentially along the longitudinal axis X, or the combustion chamber 4 is oriented at an acute angle relative to this longitudinal axis, or the combustion chamber 4' is transverse to this longitudinal axis X. In all cases, the injection device 2 is mounted on the annular bottom of the annular combustion chamber 4, 4', 4" or on the casing between the compressor 101 and the high-pressure turbine 102, 103, 104.

[0034] like Figure 2 As shown, the injection device can be an injection device comprising an inner channel 6 and an outer annular channel 8. The outer channel 8 is centered on the inner channel 6, and in the case of a tubular channel, the inner channel 6 and the outer annular channel 8 are coaxial. These channels lead to Figure 1 The combustion chamber 4, 4', 4" of the device. The inner channel and the outer channel have a circular cross section. Ignition means (not shown) allow the gas leaving the channel to be ignited to initiate combustion.

[0035] In the present disclosure, the injection device 2 is used in a configuration in which a rich mixture of gaseous hydrogen-air is injected into the inner passage 6, while air is injected into the outer passage 8. Thus, the combustion includes a first hydrogen-rich combustion at the outlet of the inner or central passage 6 and a second "lean" combustion performed around the flame produced by the first combustion.

[0036] For the injection into the internal passage 6 and the combustion at the outlet of this passage, the injection and combustion are considered rich when there is an excess of gaseous hydrogen compared to combustion occurring at a stoichiometric ratio between gaseous hydrogen and gaseous oxygen in the air, and the injection and combustion are considered lean when there is an excess of gaseous oxygen compared to this stoichiometric combustion. Stoichiometric combustion is defined as combustion in which the correct number of hydrogen atoms and oxygen atoms are required to consume all of the fuel, and only water and nitrogen remain in the combustion products.

[0037] according to Figure 3 The present invention therefore provides an injection method, which includes injecting a gaseous hydrogen-air mixture 12a richer in hydrogen than the stoichiometric level into the inner channel 6 of the injection device, and injecting air 26a into the outer annular channel 8 so as to generate a first flame front 30 produced by rich combustion at the outlet of the inner channel 6, which is surrounded by a second flame front 31 produced by lean combustion.

[0038] Thus, the inner channel 6 forms an injection pipe for the gaseous hydrogen-air rich mixture 12 a and the outer annular channel 8 forms an injection pipe for the air 26 a .

[0039] A rich mixture 12 a of gaseous hydrogen and air is injected from an inlet 10 located at the upstream end of the internal passage 6 .

[0040] The inner channel 6 has an inner diameter d. The choice of the inner diameter d of the channel depends on the desired thermal energy.

[0041] Return to Figure 2 , the downstream end 16 of the inner channel 6 is arranged upstream relative to the downstream end 24 of the outer annular channel 8. The downstream end 24 of the outer annular channel 8 is arranged at a distance r from the downstream end 16 of the inner channel 6 in the downstream direction. The outer annular channel 8 has an inner diameter D.

[0042] The outer annular channel 8 is configured to receive a second gas, which is air 26a. This gas enters the outer annular channel through an inlet 26a arranged at the upstream end of the outer annular channel.

[0043] An external swirler 28 is housed at the upstream end of the outer annular channel 8. This swirler may be radial or axial. The annular swirler 28 is arranged at a distance L from the downstream end 36 of the outer annular channel 8. The air 26a passing through the outer annular channel is rotated by the external swirler 28. This creates a vortex system that will help separate the second flame front from the outlet of the central channel.

[0044] The gaseous hydrogen-air premix 12a is injected into the internal channel 6 formed by the tube forming the central injection duct. The premix richness level is greater than 2, ie greater than 2 masses of hydrogen per 1 mass of air, and in certain operating configurations can even be greater than at least 4.

[0045] The pure air 26a injected into the annular passage 8 around the inner passage 6 is injected in an amount calculated to achieve an overall injection richness level between 0.15 and 0.5, which corresponds to an overall lean combustion. The pure air 26a is swirled within the annular passage 8 by an axial or radial external swirler 28 located upstream of the exit plane 16a of the downstream end 16 of the central duct for injection of a rich mixture of gaseous hydrogen-air.

[0046] Here, the lip 16 of the inner channel 6 is set back relative to the outlet plane 24 a of the annular channel 8 .

[0047] The following is based on Figure 3 Describe the operation of the injection device:

[0048] The injection of a rich premix 12a of gaseous hydrogen-air into the internal passage 6 makes it possible to generate, after ignition, a first flame front 30 produced by a rich combustion of said mixture at the outlet of the internal passage 6. This flame front is attached to the lip 16 of the internal passage 6. Such rich combustion, for example at a richness level greater than 2, is carried out at a flame front temperature below 1800 K in order to avoid the production of nitrogen oxides. The flame front 30 is laminar and does not suffer from diffusion-thermal instabilities due to a Lewis number greater than 1.

[0049] The injection of air 26a at the outer annular passage 8 allows the combustion gases produced by the combustion of the rich premixture to be quickly diluted and limited. The presence of a strong turbulent shear layer makes it possible to reduce the local richness. This mixture then burns and produces a second flame front 31 from a lean combustion. Due to the turbulent quenching caused by the air provided and due to the high reactivity of gaseous hydrogen, this flame front remains stable despite the strong flame stretching. This second flame front produced by lean combustion is also at a temperature below 1800K, thereby limiting the formation of nitrogen oxides. The flame front 31 is turbulent and does not attach to the lip 16 of the inner passage 6. The length of the flame will depend on the entry conditions of the fuel and the oxidant, in particular on the momentum ratio, the retreat of the inner passage relative to the outer annular passage and the presence of vortices in the flame.

[0050] The creation of these two flame fronts (rich flame 30 and lean flame 31) makes it possible to distribute the thermoacoustic load generated by the combustion over a larger surface area and thus reduce the noise pollution generated by the combustion. Similarly, the stabilization of the two flame fronts at the burner lip divides the thermoacoustic load associated with the combustion and reduces the noise generated.

[0051] Thus, the combustion method herein achieves staged hydrogen combustion by burning a gaseous hydrogen-air rich premix in a first zone (inner flame 30) and burning residual gas in a second zone (flame 31 surrounding flame 30) so as to bypass the nitrogen oxide forming zone.

[0052] The risk of flashback is limited in the case of rich combustion, since the first flame front does not have diffusion-thermal instabilities. Therefore, the speed of the first flame is not accelerated by instabilities.

[0053] The integrity of the combustion chamber is also ensured because by performing combustion at high and low richness levels, the flame temperature is lower than if combustion were performed under stoichiometric conditions. The potential flame front originating from the stoichiometric partition does not attach to the lip of the injector, which limits damage to the injector.

[0054] For operation under typical conditions of a gas turbine of a turboprop engine, an exemplary embodiment provides for a gaseous hydrogen-air mixture injected by the internal passage 6 a richness level of about 4 in the rich region, i.e. a richness well above the stoichiometric richness level 1, and supplies air by means of the annular passage 8 in such an amount that the overall richness level is fixed between 0.15 and 0.50, depending on the operating point of the turboprop engine.

[0055] Figure 4 Various possible embodiments of the outlet of the inner channel 6 for ejecting the premix are shown. The shape and thickness of the outlet 16 of the inner channels 16a, 16b, 16c can be relative to Figure 4 (A) The basic shape of the internal passage 16 is adjusted. Figure 4 In (B), the end 16a of the inner passage is formed as an inwardly inclined surface, while Figure 4 In (C), the end portion 16b continues to open outwardly at an inclined surface. Figure 4 (D) the end 16c of the internal passage is flared outwards but has an end face perpendicular to the longitudinal axis of the passage. These different configurations allow the attachment of the first flame front 30 to the lip 16 to be managed depending on the configuration of the injection system.

[0056] exist Figure 4 In (E), a cyclone 17 is added in the inner channel 6 to homogenize the gaseous hydrogen-air premix.

[0057] As for the external channel 8, it can be opened outward from the wall 240, such as Figure 5 As shown, the channels can have different outlet lip configurations:

[0058] Figure 5 (A) straight outlet 24, Figure 5 (B) in the expanded conical inclined outlet 24a, or as Figure 5 (C) The narrowing conical outlet 24b. These different configurations allow the exit velocity of the air around the rich flame leaving the internal passage 6 to be adjusted.

[0059] The present disclosure therefore relates to a method for injecting gaseous hydrogen premixed with air for an aviation gas turbine based on staged combustion, wherein:

[0060] a. Combustion of the gaseous hydrogen-air premix at high richness occurs in the first zone and produces a first flame front attached to the lip of the injector;

[0061] b. Rapidly mix the combustion products by injecting air for combustion in the second zone while producing a stable second flame front.

[0062] This method specifically allows:

[0063] a. Obtain an aerodynamically stable flame over a wide operating range,

[0064] b. Achieve combustion with extremely low nitrogen oxide emissions,

[0065] c. Avoid the risk of flashback of the second flame front,

[0066] d. Reduce noise pollution associated with hydrogen combustion,

[0067] e. Ensure the integrity and service life of the injector.

[0068] The method defined in the claims is not limited to the above description and can in particular be applied to injection systems which are arranged in the rear walls of combustion chambers or extend beyond these walls.

Claims

1. An injection method for an injection device in a combustion chamber (4, 4') of an aircraft turbine engine (1), the injection device comprising an inner channel (6) surrounded by an outer annular channel (8), the channel opening into the combustion chamber (4, 4') of the gas turbine, characterized in that The injection method includes injecting a gaseous hydrogen-air mixture (12a) having a hydrogen richness level greater than the stoichiometric amount into the inner passage (6), and injecting air into the outer annular passage (8), thereby generating, after igniting the mixture at the outlet of the inner passage, a first flame front (30) produced by rich combustion at the outlet of the inner passage (6), outside the inner passage and attached to a lip at the outlet of the inner passage, the first flame front being surrounded by a second flame front (31) produced by lean combustion when the air leaves the outer passage.

2. The spraying method according to claim 1, characterized in that: The gaseous hydrogen-air mixture (12a) has a hydrogen richness level greater than two.

3. The spraying method according to claim 1, characterized in that: The gaseous hydrogen-air mixture (12a) has a hydrogen richness level greater than or equal to 4.

4. The spraying method according to claim 1, 2 or 3, characterized in that: The air flow rate in the outer annular channel is selected so that the overall richness level at the outlet of the inner channel (6) / outer annular channel (8) assembly is set between 0.15 and 0.5 depending on the operating point of the turbine engine.

5. The spraying method according to any one of the preceding claims, characterized in that The injection of the gaseous hydrogen-air mixture (12a) and the device are configured to produce, after ignition of the mixture, at the outlet of the inner passage (6) the first flame front (30) produced by rich combustion of the mixture and attached to the lip (16) of the inner passage (6).

6. The spraying method according to claim 5, characterized in that: The gaseous hydrogen richness of the mixture is selected such that the rich combustion occurs at a flame front temperature below 1800K.

7. The spraying method according to claim 5 or 6, characterized in that: The gaseous hydrogen richness of the mixture is selected so that the first flame front (30) is laminar and has a Lewis number greater than 1, thereby limiting diffusion-thermal instabilities.

8. The method according to claim 5, 6 or 7, characterized in that: The mixture combusting in the first flame front produces residual gas which combusts in the second flame front (31) which is stabilized by supplying air from the outer annular passage.

9. The spraying method according to claim 8, characterized in that: The second flame front is maintained at a temperature below 1800K.

10. The spraying method according to claim 8 or 9, characterized in that: The air ejected from the annular passage is swirled by an annular swirler (28).

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