Multi-phase, multi-fuel injector for fuel agnostic combustion systems

Abstract

The invention relates to an injector configured to inject liquid fuel, gaseous fuel and an oxygen-comprising gas into a combustion chamber. The injector (1) comprises an atomizer (10), configured to discharge a spray of liquid fuel, one or more gaseous fuel outlets (20) concentrically positioned around the atomizer (10), a swirl generator (30) to discharge a swirling oxygen-comprising gas flow. The injector (1) comprises axial injection outlets (40) configured to discharge an axial oxygen-comprising gas flow parallel to a central body axis (B). The axial injection outlets (40) are concentrically positioned with respect to the central body axis (B), around the central atomizer (10) and within the one or more gaseous fuel outlets (20).

Description

[0001] Multi-Phase, Multi-Fuel Injector for Fuel Agnostic Combustion Systems

[0002] FIELD OF THE INVENTION

[0003] The invention relates to an injector being configured to inject liquid and gaseous fuel. The invention further relates to a combustor, a boiler, an engine and an aircraft comprising such an injector. The invention further relates to a method of operating such an injector.

[0004] BACKGROUND OF THE INVENTION

[0005] Hydrocarbon fuels like kerosene and natural gas are currently the dominant energy sources used for aeronautical propulsion and for many land-based gas turbine-based energy systems. To reduce the environmental impact of aviation and power generation, sustainable aviation fuels with a reduced carbon footprint are increasingly being introduced as partial or full replacements for such conventional hydrocarbon fuels.

[0006] Hydrogen is emerging as a promising carbon-free energy carrier for future combustion systems. In particular, premixed hydrogen combustion offers the potential for high efficiency and low carbon emissions. However, the use of hydrogen as a fuel in combustion systems is limited due to its scarce availability. . Hydrogen exhibits a high flame speed, high diffusivity, and high reactivity, which substantially increase the risk of flashback in premixed combustion system, particularly in swirl-stabilized combustors. In addition, the altered flame dynamics and flow-flame interaction associated with hydrogen combustion require careful control of the local flow field to ensure stable and predictable flame anchoring.

[0007] Conventional fuel injectors and burners, in particular swirl -based premixed injectors, are typically designed for liquid and / or gaseous hydrocarbon fuels and rely on fixed geometries to generate recirculation zones for flame stabilization. When operated with hydrogen or hydrogen-rich fuel mixtures, such premixed injectors exhibit a marked increase in flashback propensity due to the lower axial flow velocities with respect to the flame speed and the presence of recirculation regions in the vicinity of the injectorcentreline. As such, conventional hydrocarbon fuel injectors and burners are unsuitable for hydrogen combustion.

[0008] Consequently, many known hydrogen-capable combustion systems rely on fuel staging, pilot flames, separate hydrogen injectors, or reduced levels of premixing, and are therefore constrained to restricted operating envelopes. Reduced premixing and staged combustion concepts may further lead to increased non-CCh emissions due to locally fuel-rich or high-temperature combustion regions. This limits the ability of such systems to combine wide fuel flexibility with low emissions using a single injector architecture.

[0009] At present, the global supply of hydrogen produced from renewable energy sources is also limited which makes large-scale deployment difficult. Specifically in aviation, operational constraints may arise, as hydrogen may not be available at all airports or in all regions. In addition, on-board storage hydrogen presents yet another significant challenge. In particular, for long-range aircraft, where storing the quantities of hydrogen required for an entire flight cycle necessitates bulky and complex storage systems.

[0010] In view of these constraints, there is a need for multifuel combustion systems capable of operating with both liquid hydrocarbon fuels, including kerosene and other sustainable aviation fuels (SAFs), and gaseous fuels, including pure hydrogen and natural gas or a mixture comprising either thereof. In particular, there is a need for versatile aircraft and propulsion systems that can operate fuel-agnostically with liquid fuels, gaseous fuels including pure hydrogen, or any mixture thereof, depending on fuel availability and mission requirements.

[0011] Dual-fuel and multi-fuel combustion systems are known in the art, including systems capable of operating with liquid fuels and gaseous fuels. However, known solutions generally lack the capability to safely and reliably operate across the complete fuel blending range, especially when operating with mixtures of hydrogen and other hydrocarbon fuels under technically premixed conditions, from 0% hydrogen to 100% hydrogen using a single injector architecture. Prior-art systems do not provide a means to actively control the internal flow field of the injector to suppress flashback while maintaining technically premixed hydrogen combustion and stable flame anchoring.Prior art also identifies, water injection as a proposed method to reduce combustion temperatures, nitrogen oxide emissions, and flashback propensity. However, known water injection concepts are typically implemented as separate injection systems or as combustor-level features and are not integrated into the liquid fuel injection path in a manner that enables safe operation under full-hydrogen conditions while maintaining injector thermal integrity.

[0012] Accordingly, there remains a need for a multifuel, multiphase injector capable of operating with liquid hydrocarbon fuels, and gaseous fuels or mixtures thereof, particularly for operation with kerosene and pure hydrogen, over the complete range of fuel blending ratios (from 0% hydrogen to 100% hydrogen), while providing active control of flame stabilization, flashback prevention, and combustion emissions using compact and robust injector architecture.

[0013] Such dual fuel burners and combustion systems are known from the prior art, for instance from EP0933593, JP4728176B2, JP2012031730A, EP173670B1, US9121611B2, JP6023566B2, JP6004920B2, JP6190670B2, EP2846022B1, EP2706295B1, CN101713546B, CN102635860A, CN104949152A, JP6033887B2, JPWO2015037295A1, EP4350218A1, US11976820B2, EP4317786A1, EP3832208A1, US20140090381A1, US5833141A, EP1391657A2, and DE102023114595B3.

[0014] Further publications are available and provided below.

[0015] Sedlmaier, J., Habisreuther, P., Zarzalis, N., and Jansohn, P., 2014, “Influence of Liquid and Gaseous Fuel on Lifted Flames at Elevated Pressure Stabilized by Outer Recirculation,” ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 4A: Combustion, Fuels and Emissions, https: / / doi.Org / 10.l 115 / GT2014-25823

[0016] Asai, T., Miura, K., Matsubara, Y., Akiyama, Y., Karishuku, M., Dodo, S., Okazaki, T., and Tanimura, S., 2016, “Development of Gas Turbine Combustors for Fuel Flexibility,” Mitsubishi Hitachi Power Systems, Ltd., 8th International Gas Turbine Conference,https: / / etn.global / wp-content / uploads / 2018 / 09 / Development-of-gas-turbine-combustors-for-fuel-flexibility-2.pdf.

[0017] Frenillot, J. P., Cabot, G., Cazalens, M., Renou, B., and Boukhalfa, M. A., 2009, “Impact of H2 Addition on Flame Stability and Pollutant Emissions for an Atmospheric Kerosene / Air Swirled Flame of Laboratory Scaled Gas Turbine,” International Journal of Hydrogen Energy, 34(9), pp. 3930-3944, https: / / doi.Org / 10.1016 / j.ijhydene.2009.02.059.

[0018] Burguburu, J., Cabot, G., Renou, B., Boukhalfa, A. M., and Cazalens, M., 2011, “Effects of H2 Enrichment on Flame Stability and Pollutant Emissions for a Kerosene / Air Swirled Flame with an Aeronautical Fuel Injector,” Proceedings of the Combustion Institute, 33(2), pp. 2927-2935, https: / / doi.Org / 10.1016 / j.proci.2010.07.019.

[0019] “Experiments at IMFT: Scirocco” [Online], Available: https: / / cerfacs.fr / scirocco / index. php?id=experiments.

[0020] Feng, L., Qiang, Y., Xiao, L., Ming-jia, L., Jun-hui, R., and Ya-jun, L., 2022, “Experimental Study on Fuel-Switching of Dual-Fuel Gas Turbine Combustor,” Front. Energy Res., 9, https: / / doi.org / 10.3389 / fenrg.2021.796220.

[0021] Chong, C. T., Chiong, M.-C., Ng, J.-H., Tran, M.-V., Valera-Medina, A., Jozsa, V., and Tian, B., 2020, “Dual-Fuel Operation of Biodiesel and Natural Gas in a Model Gas Turbine Combustor,” Energy Fuels, 34(3), pp. 3788-3796, http s : / / doi . or g / 10 , 1021 / acs . ener gy fuel s .9b 04371.

[0022] Antoshkiv, O., Poojitganont, Th., Jehring, L., and Berkholz, C., 2017, “Main Aspects of Kerosene and Gaseous Fuel Ignition in Aero-Engine,” Aeronaut, j., 121(1246), pp.

[0023] 1779-1794, https: / / doi.org / 10.1017 / aer.2017.113.

[0024] However, the prior art fails to disclose a solution which is capable of handling blends of liquid fuel, e.g. kerosene, and technically pre-mixed gaseous fuel, e.g., hydrogen, in any blending ratio from 0% to 100% in a safe, reliable and efficient manner.SUMMARY OF THE INVENTION

[0025] An object of the invention is to provide an injector that is configured to handle blends of liquid fuel and gaseous fuel in any blending ratio from 0% gaseous fuel to 100% gaseous fuel in a safe, reliable and efficient manner.

[0026] According to an embodiment there is provided an injector (1), the injector (1) being configured to inject liquid fuel, gaseous fuel and an oxygen-comprising gas into a combustion chamber, the injector (1) having a central body axis (B), the injector (1) comprising

[0027] an atomizer (10), configured to discharge a spray of liquid fuel, the atomizer (10) being positioned at the central body axis (B),

[0028] one or more gaseous fuel outlets (20), configured to discharge gaseous fuel, being concentrically positioned around the atomizer (10),

[0029] a swirl generator (30), configured to discharge a swirling oxy gen-comprising gas flow, the swirl generator (30) being concentrically positioned with respect to the central body axis (B), around the one or more gaseous fuel outlets (20), wherein the injector (1) further comprises axial injection outlets (40) configured to discharge an axial oxygen-comprising gas flow in a direction parallel to the central body axis (B), the axial injection outlets (40) being concentrically positioned with respect to the central body axis (B), around the central atomizer (10) and within the one or more gaseous fuel outlets (20).

[0030] The injector is able to handle fuel blends ranging from 0% to 100% gaseous fuel. In particular, the injector may be operable across a continuous fuel blending range, ranging from 0% to 100% gaseous fuel. Furthermore, the composition of the gaseous fuel may comprise a mixture of two or more gaseous fuels, or comprise purely a single gaseous fuel, e.g. pure hydrogen. Different fuel blend ratios result in different flame properties, in particular different flame velocities and flame topologies, as well as different combustion products composition. The injector is capable of adapting the amount of oxygen-comprising gas passing through the swirler and the axial injection outlets, which subsequently enables adaption of the internal flow field of the injector for different fuel compositions, thereby enabling control of the position of the flame front and preventing flashback and blow out to ensure optimal combustion.The term atomizer is used to refer to a device that is configured to convert a liquid into a fine spray or mist. Preferably, the spray comprises liquid droplets with an average size of 0.1 mm or smaller. Atomizers are responsible for breaking down the liquid fuel into small droplets, which allows for better mixing with the oxygen-comprising gas. This improved mixing leads to more efficient and complete combustion, contributing to the performance and efficiency of the combustion and reducing the pollutant emissions.

[0031] The injector has a central body axis B, defining a longitudinal or axial direction. The injector has one outlet direction, being the direction which is configured to be directed to the combustion chamber. The term concentric is used with respect to this central body axis.

[0032] The atomizer is positioned centrally along the central body axis B of the injector. The atomizer is configured to generate a spray of liquid fuel substantially in the axial direction with respect to the central body axis towards a combustion chamber when present. The spray of liquid fuel generated has an angle of aperture in the radial direction with respect to the central body axis, creating a cone-shaped spray of liquid fuel.

[0033] The one or more gaseous fuel outlets are concentrically positioned around the central body axis, surrounding the atomizer. Any suitable number of gaseous fuel outlets may be provided. There may be a single gaseous fuel outlet formed as a circular orifice. Alternatively, there may be a plurality of gaseous fuel outlets, preferably formed as nozzles. There may for instance be eight, ten, twelve or more gaseous fuel outlets or nozzles, in order to allow for an as much as possible axisymmetrical distribution of the fuel and therefore sufficient mixing with the oxygen comprising gas. The number of gaseous fuel outlets may be chosen to provide an optimal balance between generating an axisymmetrical distribution of the gaseous fuel while limiting the pressure drop and ensuring sufficient fuel injection momentum and the manufacturability of small holes to keep constant injection momentum.

[0034] The swirl generator, which may also be referred to as a radial swirl generator, is concentrically positioned around the central body axis, with the swirling flow generatinga crossflow with the gaseous fuel outlets. The swirl generator may comprise a number of swirler vanes that are configured to generate a flow having a tangential velocity component with respect to the central body axis B. By changing the swirler vanes (number and / or angle), the swirl number of the flow can be varied.

[0035] The axial injection outlets are concentrically positioned around the central body axis B and are configured to generate an axial flow in a direction parallel to the central body axis B. The axial injection outlets are configured to discharge an oxygen-comprising gas flow in an axial direction with respect to the central body axis B of the injector.

[0036] The gaseous fuel outlets and axial injection outlets are preferably positioned in a common plane perpendicular to the central body axis B.

[0037] Described differently, the atomizer for the liquid fuel is positioned at the central body axis, the axial injection outlets are concentrically positioned with respect to the central body axis at a first radial distance from the central body axis, the one or more gaseous fuel outlets are concentrically positioned with respect to the central body axis at a second radial distance from the central body axis and the swirl generator is concentrically positioned with respect to the central body axis at a third radial distance from the central body axis, wherein the first radial distance is smaller than the second radial distance and the second radial distance is smaller than the third radial distance. It will be understood that there may be some level of variation in the first, second and third radial distance. For instance, the one or more gaseous fuel outlets or axial injection outlets may be provided in two or more concentric circles.

[0038] The addition of axial injection outlets to provide an axial oxygen-comprising gas flow is beneficial to control the location of the flame front with respect to the inj ector and thereby decrease or even eliminate the risk of flashback. Controlled supply of oxygen-comprising gas flow via the axial injection outlets enables control of axial flow momentum, swirl intensity, recirculation behavior, and flame anchoring characteristics within the combustion chamber. The axial injection outlets are configured to control the location of the flame front.The term flashback refers to the undesirable condition where the flame propagates back towards the injector instead of remaining at the desired position with respect to the injector. This occurs when the local flame speed exceeds the local flow velocity of the fuel-oxygen comprising gas mixture, potentially causing overheating of the injector, damage to burner components, and even explosions. Because of the relatively high flame speed of hydrogen, this is a serious risk when adding hydrogen to the fuel blend. This risk is further increased by the presence of a swirl, which typically generates low axial velocities at the centre of the combustion chamber and may even exhibit a back flow towards the injector at the centre, i.e. along the central body axis. In particular when creating a swirl with a high swirl number, there is the risk of vortex breakdown that may create a recirculation zone and thus recirculation towards the injector. This worsens the flashback propensity. By using the axial injection outlets to discharge an axial oxygencomprising gas flow this risk can be eliminated.

[0039] The axial injection outlets are preferably positioned close to the atomizer. At this position, close to central body axis the axial injection outlets are most efficient in preventing flashback by increasing the axial velocities in the center. Preferably, the axial injection outlets are positioned at a radial distance Ri with respect to the central body axis B, where the one or more gaseous fuel outlets are positioned at a radial distance R2 with respect to the central body axis B, where a ratio R12 < 2 / 3, preferably R12 < ’A, with R12 = R1 / R2. Selecting these values for R12 also allow for a proper mixing of the air from the swirl generator with the gaseous fuel from the gaseous fuel outlets before it is further mixed with the air coming from the axial injection outlets.

[0040] The injector as provided is capable of handling a wide range of fuels. It can operate on 100% gaseous fuel, in particular hydrogen, or 100% liquid fuel, in particular kerosene, or any mixture ratio of the two. It can operate under lean (technically) premixed conditions when operating with 100% H2 (or other gaseous fuels). It is a highly versatile injection system that can easily and quickly change the mixing ratio of the liquid and gaseous fuel. This is advantageous as it allows aircraft to (mainly) run on an environment-friendly fuel on and close to an airport, thus minimizing or completely getting rid of pollutants like CO, unbumt hydrocarbons and soot, while running on kerosene or other liquid hydrocarbon fuel in mid-flight.According to an embodiment the atomizer (10) is a pressure-swirl atomizer.

[0041] A pressure-swirl atomizer, also known as a SIMPLEX atomizer, is an atomizer in which liquid fuel is injected into the atomizer at high pressure. The liquid fuel then enters a swirl chamber which is configured to give a rotational motion to the fuel flow. The swirl may be created by tangentially oriented slots or vanes. The rotational motion causes the liquid fuel to spread outwardly, forming a thin, cone of liquid. As the fuel exits the nozzle, the thin film of liquid breaks up into fine droplets, creating a spray or mist. Such atomizers generate a fine droplet size in a uniform spray pattern. These types of atomizers are relatively simple in design and operation, making them reliable and easy to maintain, and are commercially available.

[0042] According to an embodiment the one or more gaseous fuel outlets (20) are configured to discharge hydrogen, syngas and / or biogas and wherein the atomizer is configured to discharge kerosene and / or a liquid sustainable aviation fuel.

[0043] Hydrogen is a versatile and clean fuel that can be used in various applications, from powering vehicles, including aircraft, to generating electricity in a power plant using gas turbines. It may be produced through several methods, each with different environmental impacts. Green hydrogen is produced using renewable energy sources, such as wind or solar power, to electrolyze water, resulting in zero carbon emissions. Blue hydrogen is generated from natural gas through a process called steam methane reforming, where the carbon dioxide produced is captured and stored, reducing its environmental footprint. Grey hydrogen, on the other hand, is also produced from natural gas but without capturing the carbon emissions, making it less environment-friendly. Many more “colours” of hydrogen are known. The term hydrogen as used here encompasses hydrogen of all origins.

[0044] Biogas is a gas produced through the anaerobic digestion or fermentation of organic matter, such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, or food waste. The primary components of biogas are methane (CTL) and carbon dioxide (CO2).Syngas, or synthesis gas, is a mixture of gases primarily composed of hydrogen (JL), carbon monoxide (CO), and often some carbon dioxide (CO2). It's produced through the gasification of carbon-containing materials such as coal, biomass, or natural gas.

[0045] Kerosene is a flammable hydrocarbon liquid obtained through the fractional distillation of petroleum. It primarily consists of hydrocarbons with carbon chain lengths between C9 and Cl 6, including alkanes, cycloalkanes, and aromatic hydrocarbons. Kerosene is widely used as a fuel for jet engines.

[0046] Sustainable aviation fuel is a type of synthetic fuel, specifically a biofuel produced from renewable resources such as plant oils, waste oils, agricultural residues, and even municipal waste, which resemble the properties of kerosene and therefore can be blended with kerosene, or substitute kerosene, for powering aircraft.

[0047] According to an embodiment the swirl generator (30) is configured to discharge a swirling oxygen-comprising gas flow, which swirling oxygen-comprising gas flow swirls around the central body axis (B).

[0048] The swirling oxygen-comprising gas flow serves the purposes of providing oxygen to the mixture and improving mixing of the fuels and the oxygen by the swirling motion. The swirling oxygen-comprising gas flow has a velocity component in the axial direction, towards the combustion chamber when present, which improves flame stabilisation.

[0049] According to an embodiment the swirl generator (30) comprises a plurality of swirl outlets (31), wherein each swirl outlet (31) is directed towards a respective gaseous fuel outlet (20).

[0050] The swirl generator may comprise a plurality of swirler vanes, forming the plurality of swirl outlets. The number of swirl outlets may match the number of gaseous fuel outlets, in particular when a plurality of gaseous fuel outlets is provided. The swirl outlets may be positioned and orientated to be directed to respective gaseous fuel outlets such thatthe respective flows cross each other. The gaseous fuel outlets may be directed in a respective first direction and positioned at a respective first position, the swirl outlets may be directed in a respective second direction and positioned at a respective second position, the first and second directions and positions being different, such that the flows cross. Each gaseous fuel outlet and swirl outlet may have their own position and orientation.

[0051] This has the effect that the oxygen-comprising gas flow being discharged from a swirl outlet meets the gaseous fuel flow being discharged from a gaseous fuel outlet at an angle, improving mixing. The first direction may be an axial direction with respect to the central body axis and the second direction may comprise a tangential as well as a radial component. The radial component may be directed towards the central body axis.

[0052] According to an embodiment the injector (1) comprises a pre-mix chamber (50) configured to receive the liquid fuel from the atomizer (10), the gaseous fuel from the one or more gaseous fuel outlets (20), the swirling oxygen-comprising gas flow from the swirl generator (30), and the axial oxygen-comprising gas flow from the axial injection outlets (40) and discharge a mixture of liquid fuel, gaseous fuel and oxygencomprising gas.

[0053] The pre-mix chamber may comprise an inlet facing the atomizer, the gaseous fuel outlet(s), the swirl generator and the axial injection outlets and an outlet configured to discharge the mixture, preferably into a combustion chamber when present.

[0054] The pre-mix chamber may have any suitable shape. It may be shaped as a cylinder, with the cylinder body axis being aligned with the central body axis of the injector. Other shapes are conceivable as well.

[0055] According to an embodiment the pre-mix chamber (50) has a funnel shape.

[0056] The funnel shape of the pre-mix chamber may narrow (converge) in a direction away from the atomizer. The funnel shape may be a narrowing funnel shape. The funnel shape may have a narrowing cross section in a downstream direction. The funnelshaped pre-mix chamber may have a wide end forming the inlet and a narrow end forming the outlet. The flow is received through the inlet and funnelled to the outlet. This funnelling has the effect of accelerating the flow and hence increase the injection velocity of the mixture in the combustion chamber, which reduces the chance of flashback.

[0057] The funnel shape of the pre-mix chamber may widen (diverge) in a direction away from the atomizer. The funnel shape may be a widening funnel shape. The funnel shape may have a widening cross section in a downstream direction. The funnel shaped premix chamber may have a narrow end forming the inlet and a wide end forming the outlet. This has the effect of allowing sufficient space for the fuel and the oxygencomprising gas to mix, while decelerating the mixture velocity. The diverging funnel shape can be used to guide and force the opening of the swirling flow. If the swirl number is sufficiently high, the swirling flow adheres to the diverging walls of the funnel and follow the angle defined by the funnel shape. This can be used to force the flame stabilization closer to the atomizer.

[0058] The pre-mix chamber may also be shaped as a cylinder with a narrow mid-section to reduce the decay of the swirling motion of the flow. Such converging-diverging channels might be beneficial for flame stabilisation. The narrow mid-section helps to increase the flow speed and reduce the possibility of flashback occurrence. The following diverging section can be used to guide the flow and stabilize the flame closer to the atomizer.

[0059] According to an embodiment the injector (1) comprises a water inlet (60) configured to feed the atomizer (10) with liquid water.

[0060] The atomizer is thus configured to discharge any liquid fuel as well as water. The atomizer may be configured to discharge the liquid fuel and water along the same injection path and from the same outlet. The atomizer is mainly used and suitable for discharge liquid fuel, but is also used and suitable to discharge water.Discharging water from the atomizer has several advantages. The addition of water helps to reduce NOx emissions and flashback propensity, as well as to control the temperature of the atomizer, in particular to prevent overheating and consequential damaging of the atomizer. This is especially important when burning 100% gaseous fuels such as hydrogen, which may result in higher temperatures. Also, the associated higher flame velocities of hydrogen flames may result in a flame front that is (temporarily) relatively close to the atomizer, causing it to overheat.

[0061] According to an embodiment the injector (1) comprises a controller (100) configured for controlling the flow of liquid fuel, the flow of gaseous fuel, the swirling oxygencomprising gas flow and the axial oxygen-comprising gas flow.

[0062] The controller may be an electronic or computational device designed to manage, regulate, and coordinate the operation of various components or subsystems, such as valves and mass flow controllers to control a liquid or gaseous flow. The controller may receive input signals from sensors or user interfaces, processes these signals according to predefined algorithms or software, and generates output signals to actuate or control the various components or subsystems, such as valves and pressure sensors controlling the flow of liquid fuel to the atomizer, the flow of gaseous fuel to the one or more gaseous fuel outlets, the flow of oxygen-comprising gas to the swirl generator and the flow of oxygen-comprising gas to the axial injection outlets.

[0063] The controller may therefore comprise several input / output interfaces to communicate with sensors, actuators, and other peripheral devices. Inputs may include data from temperature sensors, pressure sensors, etc., while outputs may control motors, valves, orifices, etc. The controller may comprise a processing unit, which can be a microcontroller, microprocessor, or programmable logic controller (PLC). This unit executes control algorithms, which can range from simple logic operations to complex feedback control systems.

[0064] The controller may be configured to operate based on (embedded) software or firmware that defines the control logic. This software can be programmed to perform specific tasks,such as maintaining a desired temperature, controlling the operation of a combustor, or coordinating the actions of multiple subsystems.

[0065] The controller may be configured to control the flow rate of the various gaseous and liquids fuels (and / or water) and the overall amount of oxygen-comprising gas to achieve specific operation settings.

[0066] The controller may be configured to control the axial oxygen-comprising gas flow through axial injection outlets in dependence on one or more of the following

[0067] • the ratio of liquid fuel and gaseous fuel,

[0068] • a required power output of the combustor, boiler or engine,

[0069] • fuel to oxygen ratio or fuel to oxygen-comprising gas ratio,

[0070] • temperature of the oxygen comprising gas flows, and / or

[0071] • the swirl number of the swirling oxygen-comprising gas flow.

[0072] Thus, the controller allows tailored control of the conditions in the injector and, hence, the combustion chamber, enabling optimal combustion conditions, stabilising of the flame in the combustion chamber, and control flame front.

[0073] According to an embodiment the controller (100) is configured to control a mass flow rate of the axial oxygen-comprising gas flow to be in the range of 0 - 40%, alternatively in the range of 0 - 25%, of a total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow. However, an axial oxygencomprising gas flow mass flow rate in the range of 0 - 100% is also achievable. Preferably, the diameter of the axial injection outlets is scaled in correlation to the increase in mass flow rate to account for the pressure drop associated with higher axial oxygen-comprising gas flow.

[0074] Controlling the mass flow rate of the axial oxygen-comprising gas flow passing through the swirler and through the axial injection provides for sufficient ability to control the position of the flame front to avoid risking flashbacks. The axial injection outlets and associated supplies can be designed and dimensioned to be able to provide a mass flow rate in that range.The term mass flow rate is used in this text to refer to the amount of mass per unit time, expressed in kg / hour or gram / second. The mass flow rate can be defined as p-A-v, where: p is the density of the liquid or gas (mass per unit volume), A is the cross-sectional area through which the liquid or gas is flowing, and, v is the velocity of the liquid or gas through the designed cross sectional area.

[0075] According to an embodiment the controller (100) is configured to adjust the mass flow rate of the axial oxygen-comprising gas flow while keeping the total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow constant or at a desired level.

[0076] This provides for a flexible control, wherein the axial oxygen-comprising gas flow can be controlled to control the position of the flame front, while the total amount of oxygencomprising gas fed to the combustion chamber is kept at a desired level to ensure optimal combustion conditions. The desired level may change, depending on the circumstances.

[0077] According to an embodiment the controller (100) is configured to control the flow of liquid water towards the atomizer (10).

[0078] The controller may in particular initiate a flow of water to the atomizer under certain predetermined circumstances. For instance, when the injector is in operation and the mass flow rate of liquid fuel to the atomizer is zero and optionally a temperature of the atomizer exceeds a predetermined threshold temperature.

[0079] According to an embodiment the injector is suitable for use in one of a jet engine, a gas turbine or boiler.

[0080] Jet engines are a class of internal combustion engines that generate thrust by expelling high-speed jets of exhaust gases. The jet engine may comprise a combustion chamber comprising one or more injectors. The jet engine may be configured for use in an aircraft, such as an airplane, wherein the jet engine is used for propulsion.A gas turbine is an internal combustion engine that converts the energy of pressurized, high-temperature gas into mechanical energy. The gas turbine operates according to the Brayton cycle and comprises three main components: a compressor, which compresses incoming air; a combustion chamber comprising one or more injectors, where the compressed air is mixed with fuel and ignited to produce high-temperature, high-pressure gas; and a turbine, which extracts energy from the high-pressure, high temperature gas to produce mechanical work. Gas turbines may be operated with various fuels and are commonly used in electricity generation, aircraft propulsion, and mechanical drive systems.

[0081] A boiler is a system used to generate steam by applying heat energy to water. The steam produced may be used for various applications, such as heating, power generation, and industrial processes. Boilers are typically used in steam power plants, where the steam drives a steam turbine connected to an electrical generator. The key components of a boiler include a combustor chamber (furnace) comprising an injector (where fuel is burned), a boiler drum (where water is converted to steam), and various heat exchangers and piping systems.

[0082] According to a further aspect there is provided a combustor (70), comprising a combustion chamber (71) and an injector (1) according to any one of the preceding embodiments.

[0083] According to a further aspect there is provided a boiler, comprising a combustion chamber (71) and an injector (1) according to any one of the above embodiments.

[0084] According to a further aspect there is provided an engine, comprising a combustor according to the above, the engine being one of a jet engine, a turbine or a boiler.

[0085] According to a further aspect there is provided an aircraft comprising an injector (1) according to any one of the above embodiments.

[0086] The aircraft may comprise an injector as described, a combustor comprising an injector or a jet engine comprising a combustor and injector as described. An aircraft accordingto such an embodiment can easily switch between gaseous and liquid fuel. Such an aircraft may be able to use (mainly) environment-friendly hydrogen close to or at the airports, while switching to (mainly) kerosene during steady flight or the other way around.

[0087] According to a further aspect, there is provided a method of operating an injector (1) according to any one of the above embodiments.

[0088] According to a further aspect there is provided a method of operating a injector (1), wherein the method comprises

[0089] controlling a liquid fuel flow through an atomizer,

[0090] controlling a gaseous fuel flow through one or more gaseous fuel outlets, controlling a swirling oxygen-comprising gas flow through a swirl generator, wherein the method further comprises controlling an axial oxygen-comprising gas flow through axial injection outlets.

[0091] The axial oxygen-comprising gas flow may be controlled to control a location of a flame front.

[0092] By controlling a flow, a mass flow rate of the various flows is controlled. The mass flow rate of each respective flow can be dynamically controlled throughout the operation of the injector.

[0093] The method may comprise injecting the liquid fuel, gaseous fuel, water, and an oxygencomprising gas simultaneously.

[0094] According to an embodiment a mass flow rate of the axial oxygen-comprising gas flow is controlled to be in the range of 0 - 40%, alternatively in the range of 0 - 25%, of a total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygencomprising gas flow.According to an embodiment the mass flow rate of the axial oxygen-comprising gas flow is varied while the total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow is kept constant or at a desired level.

[0095] The total mass flow rate of oxygen-comprising gas is kept constant, ensuring that the total ratio of oxygen and fuel is kept at a preferred level, e.g. depending on the amount of liquid and gaseous fuel, while the distribution of the oxy gen-comprising gas over the swirl generator and the axial injection outlets is controlled to prevent flashback and blow out. It is noted that the axial velocity of the oxygen-comprising gas is kept constant (the mass flow rate is kept the same), but the swirl number and thus the associated flashback properties are controlled.

[0096] If the flame front gets too close to the injector because of a relatively high amount of hydrogen, the mass flow rate of the axial oxy gen-comprising gas flow may be increased, decreasing the tangential component of the velocity, which results in pushing the flame front further away from the injector. At the same time the mass flow rate of the swirling oxygen-comprising gas flow is reduced, ensuring that total amount of oxygen remains at the desired level. This operation contributes to a flow distribution outside the injector / inside the combustion chamber which reduces the risk of flashback. Reducing the mass flow rate of the swirling oxygen-comprising gas flow reduces the strength or amplitude of a recirculation zone.

[0097] Blow out is the opposite of flash back. Blow out may occur when the flame is extinguished due to excessive flow velocity with respect to flame velocity. This can happen if the velocity of the incoming oxygen-comprising gas-fuel mixture exceeds the flame's propagation speed, effectively "blowing" the flame out of the combustion zone.

[0098] According to an embodiment a mass flow rate of liquid water to the atomizer is initiated when a mass flow rate of liquid fuel to the atomizer is zero and / or when a temperature of the atomizer exceeds a predetermined threshold temperature.The person skilled in the art will understand that the features described above may be combined in any way deemed useful. Moreover, modifications and variations described in respect of the system may likewise be applied to a method.

[0099] BRIEF DESCRIPTION OF THE DRAWINGS

[0100] In the following, aspects of the invention will be elucidated by means of examples, with reference to the drawings. The drawings are diagrammatic and are not drawn to scale.

[0101] Fig. 1 schematically shows a cross sectional view of an injector according to an embodiment,

[0102] Fig. 2 schematically shows a view of an injector in an axial direction according to an embodiment,

[0103] Fig. 3 schematically shows a cross sectional view of an injector according to an alternative embodiment,

[0104] Fig. 4 schematically shows a cross sectional view of an combustor according to an alternative embodiment.

[0105] DETAILED DESCRIPTION OF EMBODIMENTS

[0106] Figs. 1 shows the assembly of the injector 1, which has a central body axis B, defining the longitudinal / axial direction. Fig. 2 shows a cross-sectional view in the axial direction as indicated with roman II in Fig. 1. The injector 1 has one outlet direction, being the direction which is configured towards the combustion chamber 71 (as will be described below with reference to Fig. 5). The term concentric is used with respect to the central body axis B. The atomizer 10 is positioned centrally along the central body axis B of the injector 1 surrounded concentrically by axial injection outlets 40, gaseous fuel outlets 20 and swirl generator 30. Fig. 2 shows that the axial injection outlets 40 are at a distance Ri, and the gaseous fuel outlets are at a distance R2, extending radially from central body axis B.

[0107] The atomizer 10 is configured to convert liquid fuel, which enters the atomizer 10 through a liquid fuel supply line 11, into a fine spray or mist, with a droplet size of 0.1 mm or smaller, which is then discharged substantially in the axial direction at anglebetween 60-90 degrees. The spray of liquid fuel may have a conical shape with an aperture angle in the radial direction relative to the central body axis B. A liquid fuel supply valve (not shown) may be provided to regulate the flow of fuel. The liquid fuel supply line 11 may be connected to a liquid fuel tank (not shown). The atomizer 10 as shown in Fig. ‘s 1 and 2 is a pressure swirl atomizer.

[0108] Axial injection outlets 40 are positioned concentrically around the atomizer 10 at a first radial distance Ri from the central body axis B. The axial injection outlets 40 are fluidly connected to an oxygen-comprising gas supply (not shown, e.g. a vessel suitable for containing oxygen-comprising gas) via a supply line 41. One or more liquid fuel supply valves (not shown) may be provided to regulate the flow.

[0109] The axial injection outlets 40 are configured to generate an axial flow of oxygencomprising gas in the direction parallel to the central body axis B of the injector 1.

[0110] Gaseous fuel outlets 20 are positioned concentrically around the atomizer 10 at a second radial distance R^from the central body axis B. The gaseous fuel outlets 20 are fluidly connected to a gaseous fuel supply (not shown) via a gaseous supply line 21. One or more gaseous fuel supply valves (not shown) may be provided to regulate the flow. The gaseous fuel outlets 20 are configured to discharge gaseous fuel in an axisymmetric distribution around the atomizer 10, which promotes uniform distribution and effective mixing of the gaseous fuel with the oxygen-comprising gas. There can be one or more gaseous fuel outlets 20.

[0111] The swirl generator 30 may comprise the swirl outlets 31 and swirler vanes 32. Swirl outlets 31 are positioned concentrically around the central body axis B at distance greater than R2. The swirl outlets 31 may be positioned between the swirler vanes 32 configured to impart a tangential velocity component to an oxygen-comprising gas flow. The swirl outlets 31 are fluidly connected to an oxygen containing gas supply (not shown) via a supply line 33. One or more supply valves (not shown) may be provided to regulate the flow. The supply line 33 associated with the swirl generator 30 and the supply line 41 associated with the axial injection outlets 40 may be fluidly connected to the same oxygen containing gas supply (not shown). Appropriate valves and flow splitters may beprovided to distribute the oxygen containing gas over the swirl generator 30 and the axial injection outlets 40.

[0112] The gaseous fuel outlets 20 are positioned close to the swirler vanes 32, such that the oxygen-comprising gas flow from the swirl outlets 31 directly interacts with the gaseous. This maximises the interaction between the gaseous fuel and the oxygen-comprising gas flow, allowing the gases to be technically premixed.

[0113] The gaseous fuel outlets 20 and axial injection outlets 40 are positioned in the same plane along an axis perpendicular to the central body axis B.

[0114] Fig. 1 further shows a pre-mix chamber 50. The pre-mix chamber may comprise an inlet 51 facing the atomizer, the gaseous fuel outlet(s), the swirl generator and the axial injection outlets and an outlet 52 configured to discharge the mixture, preferably into a combustion chamber when present. The pre-mix chamber is rotational symmetric about the central body axis B.

[0115] As shown in Fig. 1, the pre-mix chamber 50 has a funnel shape, i.e. the outer wall defining the pre-mix chamber 50 is tapered towards the central body axis B in a downstream direction. As such, the cross-sectional area of the pre-mix chamber 50 decreases in a downstream direction. This shape accelerates the mixed flow and increases axial velocity at the outlet 52, which may reduce flashback propensity. Alternative embodiments may include diverging funnel shapes, cylindrical shapes, or convergingdiverging shapes, depending on desired mixing characteristics and flame stabilization behaviour.

[0116] Fig. 3 shows an alternative embodiment. The same features of injector 1 as described with reference to Figs. 1 and 2 can be seen in Fig. 3. Additionally, the embodiment of injector 1 presented in Fig. 3 contains a water inlet 60. The water inlet 60 is fluidly connected to a water supply (not shown, e.g. a vessel containing water and an appropriate pump) via a water supply line 61. A valve may be provided to control the water stream through the water supply and the water inlet 60. The atomizer 10 is thus configured to discharge liquid fuel and, when desired, liquid water through the same injection path.Supplying water through the atomizer 10 may be used to reduce combustion temperature, control emissions, and decrease flashback propensity, particularly during hydrogen-rich or full-hydrogen operation. Water injection may further contribute to thermal protection of the atomizer 10 when liquid fuel flow is absent or reduced.

[0117] Fig. 4 shows an embodiment of injector 1, as described with reference to Figs. 1 and 2, with the addition of a controller 100. The controller 100 may be an electronic or computational device, designed to manage, regulate, and coordinate the operation of various components or subsystems of injector 1, such as valves to control the flow of oxygen-comprising gas, both swirl and axial, liquid fuels or water, or gaseous fuels into the premix chamber 50. Such valves (not shown) may be provided in liquid fuel supply line 11, the gaseous fuel supply line 21, the supply line 33 associated with the oxygen containing gas supply, the supply line 41 associated with the axial injection outlets 40 and, optionally, the water supply line 61 and such valves may be controlled by the controller 100. This control is indicated schematically with the dotted lines.

[0118] The controller 100 may receive input signals from sensors of the injector 1 or its parent system, or from user interfaces, and process these signals by way of predefined algorithms or software, to generate output signals allowing tailored control of the various components or subsystems of injector 1, such as in particular the valves in the respective supply lines mentioned above. The controller 100 may comprise multiple input / output interfaces for communication with sensors, actuators, and other peripheral devices of the injector 1. Inputs can include, but are not limited to, temperature sensors, pressure sensors, etc., while outputs can include, but are not limited to, control motors, valves, etc. The controller 100 may also possess a processing unit, such as a microcontroller, microprocessor, programmable logic controller (PLC), or the like. The processing unit of the controller 100 executes control algorithms, which can range from simple logic operations to complex feedback control systems. Furthermore, the controller 100 may operate based on embedded software or firmware that defines the control logic, and such software may be capable of being programmed to perform specific tasks, for example, not exceeding a maximum temperature; controlling the operation of a combustor; orcoordinating the actions of multiple subsystems, shut down the fuel lines in occasion of flashback or blowout, detect abnormal behaviour of the fuel lines.

[0119] Fig. 5 shows an embodiment of injector 1, whereby injector 1 is connected to a combustion chamber 71 to form a combustor 70.

[0120] Next, the functioning of the embodiments will be described by way of example.

[0121] The controller 100 may be configured to control the respective flows by sending appropriate control signals to the respective valves regulating the liquid fuel flow through the atomizer, the gaseous fuel flow through the available gaseous fuel outlets, the swirling oxygen-comprising gas flow through a swirl generator and the axial oxygencomprising gas flow through axial injection outlets.

[0122] The controller 100 may be configured to control the amount of axial oxygen-comprising gas flow ejected through the axial injection outlets 40 in accordance with the ratio of liquid fuel to gaseous fuel, the swirl number of the swirling fuel mixture, or both.

[0123] Adjustment of the respective flows of liquid fuel, gaseous fuel, water, and oxygencomprising gas may be achieved using the controller 100. In an embodiment, temperature information associated with the injector 1, for example, the temperature of the atomizer 10 or of components in its vicinity, may be used as an input by the controller 100 for selecting a flow distribution, such as increasing the proportion of oxygen-comprising gas supplied through the axial injection outlets 40, thereby reducing the effective swirl intensity of the flow and shifting the flame stabilization region downstream in the combustion chamber 71, or initiating the supply of water to the atomizer 10, thereby providing enhanced cooling in the region of the injector 1 and further influencing the position of the flame stabilization region. Such measures may be used to influence flame stabilization behavior, reduce flashback propensity, or provide thermal protection of injector components.

[0124] The controller 100 of Fig. 4 may provide a means to control the mass flow rate of the axial oxygen-comprising gas flow within the range of 0-40% of the total oxygen-comprising gas flow rate (axial and swirl combined), such that the total mass flow rate of oxygen-comprising gas is maintained to enable sufficient ability of the user or system to control the position of the flame front and prevent the occurrence of flashback. Additionally, the axial injection outlets 40 and associated supply lines can be designed and dimensioned such that they can provide a mass flow rate in the required range. The mass flow rate of the axial oxygen-comprising gas flow can be tailored to the blend of liquid fuel and gaseous fuel being used. For example, if the mass flow rate of the gaseous fuel is zero, the mass flow rate of the axial oxygen-comprising gas flow may be at a first rate and, if the mass flow rate of the liquid fuel is zero, it follows that the mass flow rate of the axial oxygen-comprising gas flow may be at a second rate, the second rate being higher than the first rate. By way of example, the first rate may be 0% and the second rate may be 40%, the percentages taken with respect to the total oxy gen-comprising gas flow rate (axial and swirl combined).

[0125] The controller 100 of Fig. 4 may also provide a means to adjust the mass flow rate of the axial oxygen-comprising gas flow while maintaining the total mass flow rate of the axial oxygen-comprising gas flow plus the swirling air flow constant. Thus, the axial oxygencomprising gas flow can be controlled such as to adjust the position of the flame front, whilst the total amount of oxygen being fed to the combustion chamber 71 can remain at the desired amount to ensure optimal combustion conditions.

[0126] The controller 100 of Fig. 4 may also be configured to initiate the flow of water from water inlet 60 to the atomizer 10 when the injector 1 is in operation under conditions where the mass flow rate of liquid fuel to the atomizer 10 is zero. Optionally, the controller 100 may be configured to initiate the flow of water from the water inlet 60 to the atomizer 10 when the temperature of the atomizer 10 exceeds a predetermined threshold temperature.

[0127] In operation, the swirl outlets 31, in conjunction with the swirler vanes 32, are configured to generate a swirling flow of oxygen-comprising gas having a tangential velocity component with respect to the central body axis B, creating a crossflow with the gaseous fuel outlets 20 that promotes mixing of the gaseous fuel and the oxygen-comprising gas. Alternatives to the swirl generator 30 may include a tangential entry swirler or an axialswirler. The swirl outlets 31 and swirler vanes 32 create a recirculation zone inside the combustion chamber 71, which enables an aerodynamic stabilization process for the flame. The swirl number of the flow depends on the number of swirl outlets 31 and the number and / or angle and / or height of swirler vanes 32, which can be chosen depending on the swirl number required for stabilisation of the flame. Increasing the swirl number may increase the propensity of flashback when using 100% hydrogen as the gaseous fuel, thus the swirl number should be tailored to the fuel composition being used.

[0128] The swirl number can be adjusted by increasing or decreasing the axial oxygen-comprising gas flow from the axial injection outlets 40. By adjusting the distribution of the oxygen-comprising gas between the axial injection outlets 40 and the swirl generator 30, the internal flow field of the injector 1 can be manipulated. Increasing the proportion of axial oxygen-comprising gas flow increases axial momentum near the central body axis B, suppresses low-velocity or reverse-flow regions, and reduces the swirling intensity of the fuel-oxygen comprising gas mixture, which in turn pushes the flame further downstream from the atomizer 10 of the injector 1, thereby reducing flashback propensity. Conversely, increasing the proportion of swirling oxygen-comprising gas enhances mixing and recirculation strength.

[0129] In this manner, the injector 1 is configured such that the swirl intensity, axial velocity field, and flame stabilization characteristics can be adapted to the fuel composition while using a single injector architecture. The injector 1 is operable across a continuous fuel blending range from solely liquid hydrocarbon fuel, to solely a single gaseous fuel, e.g. pure hydrogen, or a mixture of two or more gaseous fuels, without reconfiguration of injector geometry or reliance on staged combustion or separate injection hardware.

[0130] The examples and embodiments described herein serve to illustrate rather than limit the invention. The person skilled in the art will be able to design alternative embodiments without departing from the scope of the claims. Reference signs placed in parentheses in the claims shall not be interpreted to limit the scope of the claims. Items described as separate entities in the claims or the description may be implemented as a single hardware or software item combining the features of the items described.

Claims

26CLAIMS:

1. Injector (1), the injector (1) being configured to inject liquid fuel, gaseous fuel and an oxygen-comprising gas into a combustion chamber, the injector (1) having a central body axis (B), the injector (1) comprisingan atomizer (10), configured to discharge a spray of liquid fuel, the atomizer (10) being positioned at the central body axis (B),one or more gaseous fuel outlets (20), configured to discharge gaseous fuel, being concentrically positioned around the atomizer (10),a swirl generator (30), configured to discharge a swirling oxy gen-comprising gas flow, the swirl generator (30) being concentrically positioned with respect to the central body axis (B), around the one or more gaseous fuel outlets (20), wherein the injector (1) further comprises axial injection outlets (40) configured to discharge an axial oxygen-comprising gas flow in a direction parallel to the central body axis (B), the axial injection outlets (40) being concentrically positioned with respect to the central body axis (B), around the central atomizer (10) and within the one or more gaseous fuel outlets (20).

2. Injector (1) according to claim 1, wherein the atomizer (10) is a pressure-swirl atomizer.

3. Injector (1) according to any one of the preceding claims, wherein the one or more gaseous fuel outlets (20) are configured to discharge hydrogen, syngas and / or biogas, and wherein the atomizer is configured to discharge kerosene, liquid sustainable aviation fuel and / or water.

4. Injector (1) according to any one of the preceding claims, wherein the gaseous fuel comprises a mixture of two or more gaseous fuels.

5. Injector (1) according to any one of the preceding claims, wherein the injector is operable across a continuous fuel blending range, ranging from 0% to 100% gaseous fuel.

6. Injector (1) according to any one of the preceding claims, wherein the swirl generator (30) is configured to discharge a swirling oxygen-comprising gas flow, which swirling oxygen-comprising gas flow swirls around the central body axis (B).

7. Injector (1) according to any one of the preceding claims, wherein the swirl generator (30) is configured to discharge a swirling oxygen-comprising gas flow generating a crossflow with the gaseous fuel outlets (20).

8. Injector (1) according to any one of the preceding claims, wherein the swirl generator (30) comprises a plurality of swirl outlets (31), wherein each swirl outlet (31) is directed towards a respective gaseous fuel outlet (20) such that their respective flows cross each other.

9. Injector (1) according to any one of the preceding claims, wherein the injector (1) comprises a pre-mix chamber (50) configured to receive the liquid fuel from the atomizer (10), the gaseous fuel from the one or more gaseous fuel outlets (20), the swirling oxygen-comprising gas flow from the swirl generator (30), and the axial oxygencomprising gas flow from the axial injection outlets (40) and discharge a mixture of liquid fuel, gaseous fuel and oxygen-comprising gas.

10. Injector (1) according to claim 9, wherein the pre-mix chamber (50) has a funnel shape.

11. Injector (1) according to any one of the preceding claims, wherein the injector (1) comprises a liquid fuel supply line (11) configured to feed the atomizer (10) with liquid fuel.

12. Injector (1) according to any one of the preceding claims, wherein the injector (1) comprises one or more gaseous fuel supply lines (21) configured to feed the one or more gaseous fuel outlets (20) with gaseous fuel.

13. Injector (1) according to any one of the preceding claims, wherein the injector (1) comprises a water inlet (60) configured to feed the atomizer (10) with liquid water.

14. Injector (1) according to any one of the preceding claims, wherein the injector is configured to inject liquid fuel, gaseous fuel, and an oxygen-comprising gas simultaneously.

15. Injector (1) according to any one of the preceding claims, wherein the injector (1) comprises a controller (100) configured for controlling the flow of liquid fuel, the flow of gaseous fuel, the swirling oxygen-comprising gas flow and the axial oxygencomprising gas flow.

16. Injector (1) according to claim 15, wherein the controller (100) is configured to control a mass flow rate of the axial oxygen-comprising gas flow to be in the range of 0 - 40 % of a total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow.

17. Injector (1) according to any one of the claims 15 - 16, wherein the controller (100) is configured to adjust the mass flow rate of the axial oxygen-comprising gas flow while keeping the total mass flow rate of the axial oxy gen-comprising gas flow plus the swirling oxygen-comprising gas flow constant or at a desired level.

18. Injector (1) according to any one of the claims 15 - 17, wherein the controller (100) is configured to control the flow of liquid water towards the atomizer (10).

19. Injector (1) according to any one of the preceding claims, which is suitable for use in one of a jet engine, a gas turbine or boiler.

20. Combustor (70), comprising a combustion chamber (71) and an injector (1) according to any one of the preceding claims.

21. Boiler, comprising a combustion chamber (71) and an injector (1) according to any one of the claims 1 - 19.2922. Engine, comprising a combustor according to claim 21, the engine being one of a jet engine, a turbine or a boiler.

23. Aircraft comprising an injector (1) according to any one of the claims 1 - 19.

24. Method of operating an injector (1), wherein the method comprises controlling a liquid fuel flow through an atomizer,controlling a gaseous fuel flow through one or more gaseous fuel outlets, controlling a swirling oxygen-comprising gas flow through a swirl generator, wherein the method further comprises controlling an axial oxygen-comprising gas flow through axial injection outlets.

25. Method according to claim 24, wherein a mass flow rate of the axial oxygencomprising gas flow is controlled to be in the range of 0 - 40 % of a total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow.

26. Method according to any one of the claims 24 - 25, wherein the mass flow rate of the axial oxy gen-comprising gas flow is varied while the total mass flow rate of the axial oxygen-comprising gas flow plus the swirling oxygen-comprising gas flow is kept constant or at a desired level.

27. Method according to any one of the claims 24 - 26, wherein a mass flow rate of liquid water to the atomizer is initiated when a mass flow rate of liquid fuel to the atomizer is zero and / or when a temperature of the atomizer exceeds a predetermined threshold temperature.

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