Fuel conditioning and injection device for combustion chamber

Abstract

A device for injecting fuel into an air passage in which an air stream is directed toward a combustion chamber may have a fuel conditioning module configured to receive fuel. The fuel conditioning module defines a reactor chamber in which the fuel is exposed to heat to decompose at least partially. A heat source is configured to be in heat exchange relation with the fuel in the reactor chamber to provide said heat to the fuel. A fuel injector module is in fluid communication with the fuel conditioning module and is located downstream of the reactor chamber, the fuel injector module having injection orifices opening into the air passage. The fuel injected into the air passage is decomposed at least partially. A method for operating a combustor is also provided.

Description

[0001] Fuel conditioning and injection device for combustion chamber

[0002] FIELD OF THE DISCLOSURE

[0003] The present disclosure relates to combustion chambers used in gas turbine engines or piston engines. More specifically, the present disclosure relates to the fuel injection and fuel conditioning systems for combustion chambers.

[0004] BACKGROUND

[0005] Gas turbines will remain ubiquitous for air transportation due to their superior power density and reliability. Although electrification is seen as a possible way forward for decarbonizing passenger cars, heavy duty and off-highway applications, among others, may continue to require the use of piston engines due to the high energy density of liquid fuels. Gas turbines and piston engines will continue to evolve toward increased efficiency to mitigate their effects on climate change. The use of alternative fuels, such as biofuels, synfuels, ammonia and hydrogen, will also progress to further reduce greenhouse gas emissions. While these fuels may potentially provide net-zero carbon dioxide (CO2) emissions, nitrogen oxides (NOx) are still emitted and represent a harmful gas for both humans and the environment.

[0006] It has been recognized that increasing the efficiency of gas turbines may be achieved by increasing either the pressure ratio (PR) for simple cycle gas turbines, or the turbine inlet temperature (TIT) for recuperated gas turbines. Recuperated gas turbines are known to provide relatively high efficiency. Increasing the pressure ratio and / or using a recuperated cycle may result in higher combustor inlet temperature (CIT), which prohibits the use of lean premixed low NOx combustors as detailed below. For piston engines, it is recognized that increasing their efficiency can be achieved by operating at lean conditions. For spark ignited (SI) engines, this is however difficult without incurring incomplete combustion, which may lead to high unburnt hydrocarbon (UHC) content and carbon monoxide (CO) emissions as well as lower engine efficiency. Compression ignited (CI) engines can safely operate at lean conditions due to their use of non-premixed combustion, but they produce relatively large amounts of NOx and soot emissions. Low NOx emissions are possible when using lean premixed combustion systems, where the fuel and air are uniformly mixed at a lean equivalence ratio prior to combustion. This allows to minimize the local maximum temperature of the gases in the combustor, resulting in low NOx emissions due to the exponential effect of temperature on NOx formation. However, such a combustor is likely to suffer from undesirable effects such as autoignition and / or flashback, which may occur in the premixing part of the combustor if the mixing time is too long (leading to autoignition of the mixture) or the velocity is too low (leading to flashback of the flame upstream of the premixing device). These issues may be exacerbated with reactive fuels (e.g., hydrogen) due to their fast reaction times, with liquid fuels (e.g., diesel, methanol) due to the delays associated with vaporizing and mixing liquids, or at high combustor inlet temperature such as those encountered with high compression ratios or recuperated gas turbines (e.g., combustor inlet temperatures above 900 K). Flame blowout (e g., misfires) can also occur at lean conditions, resulting in a loss of efficiency.

[0007] As discussed previously, lean combustion and high inlet temperatures are expected to occur in future high-efficiency, fuel flexible gas turbines and piston engines. For applications requiring very stable combustion under any operating conditions and with any fuel, premixed combustion may not be reliably used to provide low NOx and high efficiency combustion systems. It is also recognized that non-premixed (i.e., diffusion) combustion may offer higher stability and fuel flexibility, but at the expense of high NOx emissions since combustion occurs mostly at stoichiometric (i.e., high temperature) conditions in the fuel jet. Non-premixed combustion may also generate high particulate (i.e., soot) emissions, notably with liquid fuels due to pyrolysis of the fuel droplets during combustion. Post-treatment of exhaust gases using selective catalytic reduction (SCR) and particulate filters (PF) may be used to reduce NOx and soot emissions, but the significant weight, performance penalties, capital cost and the use of an additional consumable (urea) may make this technology impractical for air transportation or low-cost piston engines.

[0008] It has been shown that NOx emissions for non-premixed flames scales with the size of the fuel nozzle, meaning that NOx may be reduced when using multiple miniaturized flames instead of a few large flames. Systems using such miniaturized non-premixed flames, henceforth named micro-mixing combustion, have demonstrated premixed levels of NOx emissions with multiple fuels and at high inlet temperatures (e.g., US 6,267,585 Bl; US 10,775,047 B2), making this an attractive approach for applications requiring low NOx emissions and high reliability. In some instances, these systems may have suffered from combustion instabilities in the form of blowout of miniaturized flames due to the increased strain-rate at these small scales, such as when using low reactivity fuels or low combustor inlet temperatures. These results indicate a trade-off between NOx emissions and combustion stability for micromixing, where reducing the size of the flames yields lower NOx but is more susceptible to blowout. Although a micro-mixing injector could be designed to suppress these instabilities at the design point of the engine, safe operation of the combustor may always be a compromise with NOx emissions, especially when considering off-design operational margins. Furthermore, due to the delays associated in mixing and vaporizing a liquid fuel with air, as well as the density of liquids being orders of magnitudes higher than gases, micro-mixing is limited to the use of gaseous fuels: if un-vaporized liquid fuels are used, their high density may result in lower injection velocities, thus poor mixing and long vaporization delays as well as increased UHC, CO and soot emissions. Finally, due to the by-design small-scale of a micro-mixing injector, micro-mixing flames are always near the fuel injector and have a large specific surface, leading to significant heat transfer from the flames towards the fuel injector requiring thermal management strategies to avoid damage.

[0009] Chemically decomposing a fuel prior to mixing with air may create favorable combustion characteristics due to the formation of dissociated species such as hydrogen which increase the general reactivity of the fuel. Previous micro-mixing systems (e g., US 10,775,047 B2) protect the injector by using a thermal barrier coating (TBC) as well as careful design of the interior passages of the injector to use the fuel for impingement cooling. Although this approach allows “pre-heating” the fuel, these systems may not take full advantage of the proximity of the fuel injector to the combustion gases. Other systems have sought to produce dissociated species directly from the main fuel source of the engine to improve the operability and reduce the emissions of gas turbine combustors. In some systems (e.g., US 6,453,660 Bl; US 2010 / 0300110A1), a plasma-generating device or plasma reformer is used to generate dissociated species directly from the main fuel source of the engine, but the electronics required for these systems lead to complexity and reliability issues. Other systems (e.g., US 5,165,224 A; US 5,207,053 A) use a catalyst to induce decomposition of the fuel which allows the cooling capacity of the fuel to be increased and coking to be reduced, but careful thermal management is required to avoid catalyst deactivation. Other systems (e.g., US 8,931,283 B2) use catalytic partial oxidation to generate a highly reactive gas. Catalytic partial oxidation, however, is exothermic and requires thermal management to avoid catalyst deactivation, and the use of multiple fuel streams. All these systems may be regarded as being relatively complex, potentially leading to increased reliability issues.

[0010] Accordingly, there is a need for a reliable combustor that can potentially provide reduced NOx emissions and relatively stable combustion at both the design and off-design operating conditions of high efficiency, high power-density, fuel-flexible gas turbines and piston engines.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 shows well-stirred reactor simulations on the effect of preheating a fuel on the thermal decomposition to hydrogen and the resulting effect on improving blowout;

[0013] Figure 2 shows a longitudinally sectioned perspective view rendering of a gas turbine combustor in accordance with an aspect of the present disclosure, showing possible embodiments of the fuel conditioning module, the micro-mixing injection module, and the heat transfer module in accordance with the present disclosure;

[0014] Figure 3 to Figure 10 are schematic longitudinal sectioned views of various embodiments of the present disclosure, including different embodiments of the fuel conditioning module, the micro-mixing fuel injector module, and the heat transfer module; and

[0015] Figure 11 shows a cut view rendering of a piston engine in accordance with an aspect of the present disclosure, showing possible embodiments of the fuel conditioning module, the micro-mixing module, and the heat transfer module.

[0016] SUMMARY

[0017] In accordance with a first aspect of the present disclosure, there is provided a device for injecting fuel into an air passage in which an air stream is directed toward a combustion chamber, the device comprising: a fuel conditioning module configured to receive fuel, the fuel conditioning module defining a reactor chamber in which the fuel is exposed to heat to decompose at least partially; a heat source configured to be in heat exchange relation with the fuel in the reactor chamber to provide said heat to the fuel; a fuel injector module in fluid communication with the fuel conditioning module and located downstream of the reactor chamber, the fuel injector module having injection orifices opening into the air passage; whereby the fuel injected into the air passage is decomposed at least partially.

[0018] Further in accordance with the first aspect, for example, The device according to claim 1, wherein the heat source is a heat transfer module configured to be heated in the combustion chamber and to release heat in the fuel conditioning module.

[0019] Still further in accordance with the first aspect, for example, the heat transfer module includes a heat transfer fluid.

[0020] Still further in accordance with the first aspect, for example, the injection orifices are on an annular surface of the fuel injector module, the annular surface defining part of the air passage.

[0021] Still further in accordance with the first aspect, for example, a central axis of a plurality of the injection orifices is radially oriented relative to a central axis of the annular surface.

[0022] Still further in accordance with the first aspect, for example, the air passage defines a flow area taken in a plane to which a vector of direction of the air stream is normal, and wherein a surface density of the injection orifices is from 5 000 to 500 000 holes per m2of the flow area, inclusively.

[0023] Still further in accordance with the first aspect, for example, a plurality of the injection orifices have a largest cross-sectional dimension ranging from 0.1 to 1.0 mm in size, inclusively.

[0024] Still further in accordance with the first aspect, for example, the largest cross-sectional dimension is a diameter.

[0025] Still further in accordance with the first aspect, for example, an insulating gap is defined between the reactor chamber and the fuel injector module.

[0026] Still further in accordance with the first aspect, for example, the fuel injector module has a fuel manifold including an annular chamber, the inj ection orifices being in fluid communication with the annular chamber.

[0027] Still further in accordance with the first aspect, for example, the device includes at least two of the fuel injector module, the air passage being between the two fuel injector modules annular in shape. Still further in accordance with the first aspect, for example, the device includes one said fuel conditioning module for each said fuel injector module.

[0028] Still further in accordance with the first aspect, for example, the air passage is annular, and wherein swirler vanes are located in the air passage.

[0029] Still further in accordance with the first aspect, for example, an air mixer is in fluid communication with the fuel conditioning module to inject air or oxy gen-containing gas in the fuel conditioning module.

[0030] Still further in accordance with the first aspect, for example, the air mixer is in fluid communication with the reactor chamber to inject air or oxygen-containing gas in the reactor chamber.

[0031] Still further in accordance with the first aspect, for example, at least one of the fuel conditioning module, the heat source and the fuel injector module has an additive manufacturing body to define an inner cavity thereof in which the fuel is received.

[0032] In accordance with a second aspect of the present disclosure, there is provided a method for operating a combustor comprising: supplying fuel to a fuel conditioning module; exposing the fuel in the fuel conditioning module to heat to at least partially decompose the fuel; injecting the fuel at least partially decomposed into an air stream; and igniting a mixture of air and of the fuel at least partially decomposed for combustion in a combustion chamber.

[0033] Further in accordance with the second aspect, for example, supplying fuel includes supplying one of pure hydrogen, ammonia, methanol, ethanol, kerosene, gasoline, diesel, biofuel, or any other compound composed at least in part of the chemical element hydrogen.

[0034] Still further in accordance with the second aspect, for example, exposing the fuel in the fuel conditioning module to heat includes absorbing heat in the combustion chamber and releasing heat in the fuel conditioning module.

[0035] Still further in accordance with the second aspect, for example, supplying fuel includes supplying a liquid fuel, and wherein exposing the fuel to heat includes vaporizing the liquid fuel. Still further in accordance with the second aspect, for example, exposing the fuel to heat includes exposing the fuel to heat such that the fuel reaches temperatures of at least 600 K and up to 1500 K, inclusively.

[0036] Still further in accordance with the second aspect, for example, exposing the fuel in the fuel conditioning module to heat includes exposing the fuel to resistance heating, infrared heating, and / or induction heating.

[0037] Still further in accordance with the second aspect, for example, air or an oxygen-containing gas may be injected in the fuel conditioning module to induce partial oxidation reactions.

[0038] Still further in accordance with the second aspect, for example, the fuel may be preheated using heat reclaimed from engine components associated with the combustor.

[0039] DETAILED DESCRIPTION

[0040] Figure 1 shows exemplary results from Well-Stirred Reactor (WSR) simulations on the blowout limits of a preheated fuel. The results show that preheating the fuel (dotted line) improves the blowout limit. When thermal decomposition of the fuel is considered, the blowout limit is further reduced depending on fuel residence time at a given temperature, and hence the combustion stability is improved. The fuel in these simulations is propane, but the results may be similar for other hydrogen-containing fuels such as methane, methanol, gasoline, diesel, jet-fuel, ammonia, and the like. The results also show that partial oxidation (POX) of the fuel under very rich equivalence ratio (here 10) may further improve blowout limit. These simulations may be used as a starting point when designing a fuel conditioning module to ensure enough residence time and temperature. The role of thermal decomposition is highlighted by showing the difference in blowout when this effect is considered (colored lines) or ignored (black dotted line). The effect of thermal partial oxidation (POX) of the fuel at high equivalence ratio (here 10) is also shown.

[0041] Figure 2 shows a longitudinal section view rendering of a device in accordance with the present disclosure that may be described in a variant as a gas turbine combustor, such that the device may be referred to herein as a gas turbine combustor, even though the combustor may be used in other applications. The device may also be referred to as a fuel conditioning and injection device. Moreover, as the device has different modules, the device could be referred to as a fuel conditioning and injection apparatus, a fuel conditioning and injection system. The expression module used herein may be substituted with other expressions such as device, unit, etc. The device includes a fuel conditioning module 10, a micro-mixing injector module 20, and a heat source such as a heat transfer module 30, which will be further described in Figure 3. This specific embodiment also optionally includes fins 32 that act as enhanced heat transfer surfaces to increase the heat exchange from the combustion products to the fuel circulating in channels 31. Here, the channels 31 may be part of a reactor 13 where fuel undergoes preheating and thermal decomposition. Other embodiments described below may also have specific enclosures that act as the thermal decomposition reactor.

[0042] Figure 3 shows a schematic of an embodiment of a proposed device in accordance with the present disclosure. Fuel F is admitted to the conditioning module 10 of the combustor by a fuel supply line(s) 1 (e.g., a pipe(s), a conduit(s), etc). Fuel F is subsequently injected in an air stream A through the micromixing injector module 20, resulting in non-premixed flames 100 that generate hot combustion products P in a primary combustion zone 200 for use in a power-producing machine such as a gas turbine or a piston engine. The conditioning module 10 is heated by the combustion products P using a heat source, such as a heat transfer module 30. The fuel F may be any hydrogen-containing compound, such as pure hydrogen, ammonia, ethanol, methanol, kerosene, gasoline, diesel, or the like. The fuel F first enters a pre-heating chamber 11, where the fuel may be partially or fully evaporated if liquid, or may be pre-heated if already gaseous. In the shown embodiment, the heat required by the pre-heating chamber 11 may be supplied by heat transfer from the products P of combusting fuel F with air A. The pre-heating chamber 11 is optional. In alternate embodiments, the heat may be provided by hot air discharged from a compressor or a recuperator, hot exhaust gases at the outlet of turbine rotor or a recuperator or a piston engine, and / or heat losses from other components of a gas turbine engine or piston engine, as examples among others, with the heat optionally provided from two or more of these heat sources (including products P), i.e., heat reclaimed from engine components. In such embodiments, at least part of the pre-heating chamber 11 may be located physically away from a remainder of the conditioning module 10, but may still considered to be part of said module 10. For starting the combustion in the device, a pilot injector 12 may be used, with for example non-conditioned fuel. The pilot injector 12 may be defined by an orifice for gaseous fuels, or a simple injector for liquid fuels, and may be activated by controlling the pilot fuel supply pressure. Once the conditioning module 10 is sufficiently hot, fuel F may be supplied to the conditioning module 10, and the pilot injector 12 may be turned off. The resulting gaseous fuel may then flow through the heat transfer module 30. While the expression “transfer” is used, other expressions could define the module 30, such as heat reclaim, heat recirculation, heat recuperation, heat capture, heat exchange. The heat transfer module 30 may consist of thermally conductive channels 31 such as arranged in coils, loops, etc., directly exposed to the combustion products P. This may be in the form of a heat sink, using heat conduction properties of a material (e.g., metal). The heat transfer module 30 may also include a heat transfer fluid circulating therein. In both scenarios, heat is absorbed at the combustion products P to then be released to the fuel F in the fuel conditioning module 10. The internal and external surfaces of these channels may contain heat transfer enhancements such as fins 32 (figure 2), but may also include pins, corrugations, and / or high roughness surfaces, different combinations of these features, as examples among others, in order to increase the convective heat transfer coefficient and the heat transfer surface. The channels 31 may also have a relatively high specific surface area, which may increase the heat exchange thermal contact area between the combustion products P and the fuel F and may reduce the residence time within the channels 31. These effects may increase the heat transfer from the combustion products P to the fuel F while reducing the formation of deposits in small channels (i.e., coking) due to the shortened residence time. The fuel F may be heated to a point where thermal decomposition starts to occur, which may be in the range of -600 K to up to -1500 K depending on its composition, for example. Thermal decomposition may occur outside of this range, depending on the composition. The fuel F returns to the conditioning module 10 where it may be allowed to undergo thermal decomposition in a reactor 13, in a chamber thereof, i.e., reactor chamber. The reactor 13 may allow sufficient residence time of the fuel F to achieve a suitably high completeness of thermal decomposition of the fuel F. This may occur continuously to generate a flow of thermally decomposed fuel, as opposed to being a batch process. The reactor 13 may be made of relatively large flow passages, mitigating the negative effects of coking that could occur here due to longer residence time. Due to the higher temperatures required, the reactor 13 may be in thermal contact only with the combustion products P, and thermally insulated from the air stream A by a gap 14 to avoid unnecessary heat losses. The gap 14 may be annular. The gap 14 may is an insulating gap and may be filled with a fluid, a foam, etc. The conditioned fuel may then be transferred to the micro-mixing injector module 20.

[0043] In an embodiment for use in a gas turbine combustor, the micro-mixing inj ector module may include the inner fuel distribution manifold 21 and the outer distribution manifold 22, each having injection orifices 23 at a downstream end. An annular passage 24 for air A may defined between the inner fuel distribution manifold 21 and the outer distribution manifold 22 of the micro-mixing injector module 20. In the schematic figures 3 to 10, a single fuel conditioning module 10 and a single heat transfer module 30 are shown for a device that has both the inner fuel distribution manifold 21 and the outer fuel distribution manifold 22, with conditioned fuel shared by the manifolds 21 and 22, via appropriate piping for example. However, each of the inner fuel distribution manifold 21 and the outer fuel distribution manifold 22 may each have a dedicated fuel conditioning module 10 and a dedicated heat transfer module 30. Moreover, while the annular passage 24 is defined by a pair of manifolds, i.e., 21 and 22, the device may have a single manifold, with the annular passage 24 being between one manifold (e g., 21 and 22) and a case or like annular wall.

[0044] The injection orifices 23 may be provided in a single row, multiple rows, etc. In a variant, as observed from Fig. 2, the orifices 23 are simply holes in an annular wall of the manifolds 21 and 22 (if both are present). Optionally, a central axis of the inj ection orifices 23 may be oriented transversely to the central axis of this annular passage 24 (shown in dotted lines in the figures). For example, the central axes of the injection orifices 23 may lie in a common plane, with a vector of the central axis of the annular air passage

[0045] 24 being normal to the common plane. The central axes of the injection orifices 23 may optionally be radially oriented. There may consequently result a cross-flow injection of fuel F into the air stream A which may form miniature non-premixed flames 100. In alternate embodiments, the axis of the injection orifices may be inclined at angles varying between -45° to +45° relative to a plane to which a vector of the central axis of the annular air passage 24 is normal. Stated differently, the central axes of the injection orifices 23 may lie in a virtual cone. There may also be a variation of orientation for the different injection orifices 23. The fuel conditioning module 10, micro-mixing injector module 20, and heat transfer module 30 may be located on radially inwardly of the annular air passage 24 and connected to an inner fuel distribution manifold 21 as is shown in Figure 3, as a possibility. The fuel conditioning module 10, micromixing injector module 20, and heat transfer module 30 may alternatively be located radially outwardly of the annular air passage 24 and connected to an outer fuel distribution manifold 22 as is shown in Figure 4. As another possibility, the fuel conditioning module 10, micro-mixing injector module 20, and heat transfer module 30 may be both radially inward and radially outward of the air circulation passage 24 (not shown). For simplicity, subsequent figures will only show the radially inward configuration, but such embodiments may also be modified in a radially outward or a dual radially inward and outward arrangement. A swirler section 25 (such as in the form of vanes) may optionally be used to induce a recirculating flow 101 downstream of the micro-mixing injector module 20, which may enhance heat transfer of the hot combustion products P with the fuel in the heat transfer module 30 and hence may increase the total amount of heat transferred to the fuel in the conditioning module 10. The combustion products P may also help stabilize the non-premixed flames 100. The injection orifices 23 may range from 0.1 to 1.0 mm in size, inclusively, i.e., 0.1 to 1.0 mm being the largest cross-sectional dimension (e g., the diameter). The surface density of the injection orifices 23 may range from 5 000 to 500 000 holes per m2of air cross-flow area, inclusively. Air cross-flow area (i.e., flow area) is here defined as the total area of the air passage 24 measured at a plane to which the vector coincident with the central axis is normal, the plane being at the location of the orifices 23. The vector may alternatively be said to define the main direction of the air flow in the air passage 24. Thus, in the embodiments of Figures 2 to 10, the air cross-flow area is annular, due to the annularity of the air passage 24. However, the air cross-flow area need not be annular, as in a variant described below for Figure 11. Moreover, while Figures 2 to 10 show an annular shape for the air passage 24, it is possible for the combustors or devices of Figures 2 to 10 to have a hollow cylindrical air passage 24, whereby the air cross-flow area would be circular. Due to the close proximity of hot air with the small injection holes, coking that may occur here may be burned off.

[0046] Figure 5 shows an alternate embodiment where the fuel F may also be preheated using an electric resistance heater 15, in addition to the heat transfer module 30. Other means of heating the fuel may be infrared heating, induction heating, or any other heating source other than the capture of heat from the combustion products P, and these heating sources may be used with the capture of heat from the combustion products P. This may allow a further increase in the temperature of the fuel F in the fuel conditioning module 10 and its reactor 13, further increasing the thermal decomposition of fuel F and hence further improving combustion stability. This effect may also be achieved using the embodiments shown in Figure 6, Figure 7, Figure 8 and Figure 9, where oxygen or gas is mixed with the fuel to achieve a richer fuel-air mixture that undergoes partial oxidation reactions that increase the reactivity of the fuel-air mixture. In Figure 6, a mixing device 40 may be used where the pressurized fuel is mixed with a relatively small amount of air A into the conditioning module 10, resulting in a richer mixture of fuel and air 41 that may undergo partial thermal oxidation in the reactor 13, resulting in a reactive gas mixture that may then be injected using the micro-mixing fuel injector module 20. The same effect may be achieved using combustion products P that may still contain significant amounts of oxygen in the case of lean combustion, as shown in Figure 7. In Figure 7, the device 40 could be referred to as an ejector, but any other device that allows the mixing of a relatively small and controlled amount of the air stream A or the combustion products P with the fuel F can be used. In the case of liquid fuels, the mixing device 40 may also be located after the fuel pre-heating chamber 11 but before the reactor 13 to allow improved mixing of the now vaporized fuel F with air A, as shown in Figure 8, or combustion products P, as shown in Figure 9. An additional benefit of mixing air A or combustion products P with the fuel F prior to injection in the primary combustion zone 200 may be a further decrease in NOx emissions due to faster mixing and reduced time at stoichiometric conditions in the fuel jets due to their higher velocity and lower stoichiometric air-fuel ratio.

[0047] Specifically for liquid fuels, the fuel may be held in a supercritical state (i.e., above its critical pressure and temperature) using a pressure-control orifice 50 between the fuel conditioning module 10 and the micro-mixing injector module 20 as shown in Figure 10. By keeping the liquid fuel in a supercritical state, flow stability issues associated with two-phase boiling flows may be avoided since the fuel may not boil in a supercritical state, resulting in a stable fuel flow to the combustion chamber.

[0048] In Figures 3 to 10, the longitudinal section views show in a simplified manner modules that may be annular. Hence, a mirror image could have been present as separated by the central axis of the device in dotted lines. The central axis’s actual position may not be exactly as shown in the figures. Thus, at least some parts of the fuel conditioning module 10, micro-mixing injector module 20, and heat transfer module 30 may be annular, in a manner similar to the device of Figure 2.

[0049] Figure 11 shows a longitudinal section view rendering of a device in accordance with the present disclosure that may be described in a variant as a piston engine combustor. Similar to the device of Figure 2, the piston engine combustor includes the fuel conditioning module 10, the micro-mixing injector module 20, and the heat transfer module 30. The piston engine may further include an air inlet valve(s) 51, a combustion products exhaust valve(s) 52, and a piston 53 used to compress the air A and / or expand combustion products P. An engine may have multiple ones of the piston engine combustor of Figure 11. Similar to previous configurations, the fuel F is admitted to the conditioning module 10 of the combustor by a fuel supply line(s). The fuel F is subsequently injected through a micro-mixing injector module 20, resulting in non-premixed flames 100 that generate hot combustion products P in a primary combustion zone 200. The micro-mixing injector module 20 may be comprised of an inner fuel distribution manifold 21, or an outer fuel distribution manifold 22, or both as shown. The fuel conditioning module 10 is heated by exposure to the combustion products P using the heat transfer module 30, which may be located after the exhaust valve(s) 52 as shown in Figure 11. The heat transfer module 30 may have a similar configuration as described above, such as with thermally conductive channels 31 in direct contact with combustion products P. In any embodiment described herein, fuel F may circulate in the heat transfer module 30 such as in thermally conductive channels 31 that extend into the combustion chamber, or a coolant may be used to transfer heat from the combustion products P to the fuel F. Other embodiments may be configured in a way that the heat transfer module 30 may be located before the exhaust valve(s) 52 and may thus be exposed to the combustion products P in the primary combustion zone 200 The heat transfer module 30 may also use an auxiliary heating system 15 such as the embodiment shown in Figure 5, and / or use a mixing device 40 such as shown in Figure 6 to Figure 9 to create a richer mixture of fuel F and air A or combustion products P that still contain oxygen, with said rich-mixture undergoing partial oxidation. Furthermore, other possible embodiments of the present disclosure include two-stroke piston engines, four-stroke piston engines, spark-ignited piston engines, compression-ignited piston engines, rotary engines, opposed-piston engines, split-cycle engines, or any other internal combustion engine that generate work by expanding hot gases in a closed volume, with said expanding hot gases generating forces on a moving surface such as a piston.

[0050] Therefore, to solve the problems associated with the prior art, the present disclosure may improve the NOx-stability trade-off of micro-mixing combustion while allowing the use of liquid fuels by recirculating, capturing or reclaiming heat from the combustion zone or any other source of waste heat, and transferring the heat to fuel, making a synergistic use of the proximity of the flames with the fuel injector in micro-mixing combustion systems. Due to their small size (high specific area), the various micro-mixing injector modules 20 and heat transfer modules 30 described herein may enable a transfer of a substantial amount of heat back towards the fuel conditioning module 10, allowing a non-negligible degree of fuel pre-heating. In an embodiment, such a system may be used in gas turbines engines with high combustor inlet temperatures, such as high pressure-ratio simple cycle gas turbines, recuperated cycle gas turbines or reheat cycle gas turbines, where the combustor inlet temperature is higher than the autoignition temperature of the fuel used (e.g., >900 K) and premixed combustion may not be used reliably to reduce NOx emissions. In another embodiment, such a system may be used in a pre-chamber ignitor for SI piston engines operating at very lean conditions, where misfires would normally occur. In another embodiment, such a system may be used as the main fuel injector for CI engines, allowing a reduction of NOx and soot emissions associated with non-premixed combustion in such engines. In another embodiment, such a system may be used in a recuperated split-cycle piston engine, where the combustion occurs either outside or inside of the expansion piston, benefiting from the fast mixing of such a device due to the short time available for combustion. The device may also be used in other applications requiring hot combustion gases, low emissions, high combustion stability, and high reliability. The present disclosure may also be used with hydrogen-carrying fuels, meaning any fuel containing the chemical compound of hydrogen, such as pure hydrogen, natural gas, propane, gasoline, diesel, kerosene, methanol, ethanol, ammonia, and the like (e.g., fuels containing hydrogen, such as NH3, CH4, C8H18, CH3OH, etc.).

[0051] . The following description is representative of the embodiments of the present disclosure.

[0052] The present disclosure includes a micro-mixing fuel injector module including multiple injection holes in the order of ~0.1 mm to ~1 mm of maximum cross-sectional dimension, inclusively. The expression micro is used herein to refer to these injection holes, but in a variant the dimensions given herein may supersede the moniker “micro”. The fuel injection holes are positioned and oriented so that fuel is injected into an air stream directly adjacent to or in a primary combustion zone where the fuel is allowed to react with the air to generate hot combustion products. The position of the fuel injection holes and their relatively small size allows fast mixing of fuel, air and combustion products. A swirler may be used to enhance recirculation of the combustion products towards the flames, improving combustion stability. Since there is no premixing duct, this approach may be intrinsically safer than fully premixed combustion due to the avoidance of flashback and autoignition of the mixture while achieving similar NOx levels due to the small- scale flames. The fuel injection module may also include internal passages and manifolds designed to distribute the fuel and heat to a large number of fuel injection holes 23 that may be referred to as miniature. Multiple fuel injector modules 20 may be independently operated in a single combustor, allowing to optimize fuel distribution in the combustor at different load conditions (fuel staging). For example: a complete combustor may be include three fuel inj ector modules 20, with only one or two of the fuel inj ector modules 20 operating at part-load, and all three fuel injector modules 20 operating at full load. Another example is the independent operation of the inner fuel distribution manifold 21 or the outer fuel distribution manifold 22, where one or both can be operated at different load conditions to optimize fuel distribution in the combustor. This may also allow to mitigate coking when using carbon-based fuels by flowing air inside the unused fuel injector modules while the engine is in operation, allowing carbon deposits to be burned off, which carbon deposit may form within the injector due to the high temperature of the injector.

[0053] The present disclosure may include a fuel conditioning module which may have a device to fully vaporize and preheat liquid fuels, henceforth named vaporizer. The vaporizer may be used to heat a liquid fuel above its boiling temperature, resulting in a gaseous fuel that may be used in the micro-mixing injector module. To achieve this effect, the vaporizer may use waste heat from engine components such as compressors, turbines, bearings, combustors, and the like. The vaporizer may also extract heat for vaporizing the fuel from combustor inlet air, which is heated either by compression in a high pressure-ratio single-cycle gas turbine, or by a recuperator in a recuperated gas turbine cycle, or by a compression piston in a piston engine. The vaporizer may also extract heat from the exhaust gases at the outlet of the turbine in a single-cycle engine, or at the outlet of the recuperator in a recuperated cycle engine, or at the exhaust gas manifold in a piston engine. The vaporizer may also be directly integrated into the fuel injector module 20, extracting heat from the primary combustion zone and providing a cooling to the injector module 20. The vaporizer may also include a throttling device, allowing to keep liquid fuels at a pressure and temperature above their critical point, resulting in a supercritical fluid which is less susceptible to two- phase flow instabilities and is fully vaporized once throttled. Once the fuel is vaporized, or if the fuel is already a gas, the fuel conditioning module 10 may also comprise a continuous-flow, small-scale reactor (e.g., reactor 13), optionally referred to as a microreactor, that may allow thermal decomposition of the fuel to be initiated at high temperature prior to injection in the combustor, further improving combustion stability characteristics of the micro-mixing injector compared to simply preheating the fuel. Due to the high temperatures required for thermal decomposition of the fuel, the reactor may be integrated into the fuel injector and may make use of the proximity of the fuel injector module 30 with the hot primary combustion zone to provide cooling to the device as well as increasing the fuel temperature to levels where thermal decomposition occurs, which depends on fuel composition but is generally in the range of >600 K to <1500 K. This integration of the reactor may make synergistic use of the small features required by micro-mixing combustion, allowing high volumetric heat transfer rates and / or low residence times to be achieved, which may be crucial to achieve high thermal decomposition rates of the fuel and / or to mitigate coke formation that may occur at high temperatures with carbon-based fuels by limiting the contact time in narrow passages at these temperatures. The fuel conditioning module 10 may also include a mixing device such as an ejector or the like, henceforth named mixer, that allows mixing either air or combustion products still containing oxygen (i.e., oxygen-containing gas) with the fuel to initiate partial oxidation, further increasing the reactivity of the fuel. The mixer is designed to dose only a small quantity of air, resulting in a fuel -rich mixture of high equivalence ratio (typically >5) to avoid too high temperatures due to the partial oxidation reaction of the fuel. The role of the fuel conditioning module, i.e., to increase the reactivity of the fuel, may be beneficial only for non-premixed or partially-premixed combustion systems such as proposed in the current disclosure. Increasing the reactivity of the fuel for fully-premixed combustion systems may result in undesired effects such as autoignition or flashback within the premixing tube.

[0054] The present disclosure may include a heat transfer module that increases the heat flow from the primary combustion zone back towards the fuel conditioning module to increase the rate of vaporization and / or thermal decomposition of the fuel. This module may include enhanced heat transfer surfaces such as fins, pins, corrugations, high surface roughness, swirlers, or any feature that increases the convective heat transfer. This module may also consist in fluid passages from the fuel conditioning system to the primary combustion zone, increasing the thermal contact area between the fuel and the combustion products and allowing to increase the advective heat transfer from the combustion products to the fuel conditioning module. This heat transfer enhancement system may be positioned in a way to also promote recirculation of products towards the module 30 as well as to serve as hot ignition surfaces for the fuel jets, both effects further increasing combustion stability.

[0055] The device of the present disclosure may be used with a controller. The controller may have a processing unit and a non-transitory computer-readable memory communicatively coupled to the processing unit and comprising computer-readable program instructions executable by the processing unit for operating the device as explained above. To do so, the controller may be connected to valves, pumps, and an electric system to ignite a flame and control a flow of air and fuel to condition and injected the fuel in the manner described above. To sustain the high temperatures involved, the device of the present disclosure may be manufactured from high-temperature corrosion resistant superalloys such as Inconel 625 or Haynes 230 or the like, from refractory metals and their alloys such as tungsten, molybdenum, and / or tantalum or the like, from ceramics such as alumina, silicon carbide or silicon nitride or the like, or from any other material that may sustain high-temperature and corrosive environments, or any combination hereof. Materials having high thermal conductivity may offer further benefits by increasing the possible heat flux to the fuel, with notable materials that are also temperature and corrosion resistant being silicon carbide or molybdenum coated with an Environmental Barrier Coating (EBC). The present disclosure may also benefit from the capabilities of additive manufacturing, where complex fluid passages and features may be manufactured easily, notably the very large number (1000’s) of small (< 1 mm) holes and the internal flow passages required by the present disclosure. The high surface roughness of this process may also be used to increase heat transfer rates. In a variant, the fuel conditioning module 10, fuel inj ector module 20, and / or the heat transfer module 30 each have an additive manufacturing body, at least to define their inner cavities in which the fuel circulates, such as a monoblock body, a well assembly of bodies, etc. To fabricate the additive manufacturing bodies, additive manufacturing methods such as 3D printing, laminated object manufacturing, and the like, may be used to efficiently manufacture the complex internal passages and manifolds described above. Additive manufacturing methods such as 3D printing, laminated object manufacturing, and the like, may thus be used to generate high surface-ratio features to increase heat transfer, increasing the conversion rate of the fuel to hydrogen and hence improving combustion stability further.

[0056] The scope of the present disclosure is not limited to the embodiments described above, and may encompasses alternative embodiments such as using a plurality of independently fueled devices to optimize fuel distribution according to the engine load (fuel staging), using an electric heater in-lieu of a pilot injector for starting the combustor under cold conditions, allowing air-injection into the device for the purpose of cleaning or creating a rich fuel-air mixture that may undergoes thermal partial oxidation in the conditioning module, or any other embodiment using the proposed arrangement of a fuel conditioning module, a micromixing fuel injector module, and a heat transfer module, for the purpose of conditioning a fuel at high temperature (vaporization and / or thermal decomposition) and injecting said fuel into an air-stream through miniature injection holes for the purpose of generating hot combustion products to be used in a powergenerating engine such as a gas turbine engine or a piston engine.

Claims

CLAIMS1. A device for injecting fuel into an air passage in which an air stream is directed toward a combustion chamber, the device comprising: a fuel conditioning module configured to receive fuel, the fuel conditioning module defining a reactor chamber in which the fuel is exposed to heat to decompose at least partially; a heat source configured to be in heat exchange relation with the fuel in the reactor chamber to provide said heat to the fuel; a fuel injector module in fluid communication with the fuel conditioning module and located downstream of the reactor chamber, the fuel injector module having injection orifices opening into the air passage; whereby the fuel injected into the air passage is decomposed at least partially.

2. The device according to claim 1, wherein the heat source is a heat transfer module configured to be heated in the combustion chamber and to release heat in the fuel conditioning module.

3. The device according to claim 2, wherein the heat transfer module includes a heat transfer fluid.

4. The device according to any one of claims 1 to 3, wherein the injection orifices are on an annular surface of the fuel injector module, the annular surface defining part of the air passage.

5. The device according to claim 4, wherein a central axis of a plurality of the injection orifices is radially oriented relative to a central axis of the annular surface.

6. The device according to any one of claims 1 to 5, wherein the air passage defines a flow area taken in a plane to which a vector of direction of the air stream is normal, and wherein a surface density of the injection orifices is from 5 000 to 500 000 holes per m2of the flow area, inclusively.

7. The device according to any one of claims 1 to 6, wherein a plurality of the injection orifices have a largest cross-sectional dimension ranging from 0.1 to 1.0 mm in size, inclusively.

8. The device according to claim 7, wherein the largest cross-sectional dimension is a diameter.

9. The device according to any one of claims 1 to 8, wherein an insulating gap is defined between the reactor chamber and the fuel injector module.

10. The device according to any one of claims 1 to 9, wherein the fuel injector module has a fuel manifold including an annular chamber, the injection orifices being in fluid communication with the annular chamber.

11. The device according to claim 1 , wherein the device includes at least two of the fuel inj ector module, the air passage being between the two fuel injector modules annular in shape.

12. The device according to claim 11, wherein the device includes one said fuel conditioning module for each said fuel injector module.

13. The device according to any one of claims 1 to 12, wherein the air passage is annular, and wherein swirler vanes are located in the air passage.

14. The device according to any one of claims 1 to 13, wherein an air mixer is in fluid communication with the fuel conditioning module to inj ect air or oxygen-containing gas in the fuel conditioning module.

15. The device according to claim 14, wherein the air mixer is in fluid communication with the reactor chamber to inject air or oxygen-containing gas in the reactor chamber.

16. The device according to any one of claims 1 to 15, wherein at least one of the fuel conditioning module, the heat source and the fuel injector module has an additive manufacturing body to define an inner cavity thereof in which the fuel is received.

17. A method for operating a combustor comprising: supplying fuel to a fuel conditioning module; exposing the fuel in the fuel conditioning module to heat to at least partially decompose the fuel; injecting the fuel at least partially decomposed into an air stream; and igniting a mixture of air and of the fuel at least partially decomposed for combustion in a combustion chamber.

18. The method according to claim 17, wherein supplying fuel includes supplying one of pure hydrogen, ammonia, methanol, ethanol, kerosene, gasoline, diesel, biofuel, or any other compound composed at least in part of the chemical element hydrogen.

19. The method according to claim 17 or claim 18, wherein exposing the fuel in the fuel conditioning module to heat includes absorbing heat in the combustion chamber and releasing heat in the fuel conditioning module.

20. The method according to any one of claims 17 to 19, wherein supplying fuel includes supplying a liquid fuel, and wherein exposing the fuel to heat includes vaporizing the liquid fuel.

21. The method according to any one of claims 17 to 20, wherein exposing the fuel to heat includes exposing the fuel to heat such that the fuel reaches temperatures of at least 600 K and up to 1500 K, inclusively.

22. The method according to any one of claims 17 to 21, wherein exposing the fuel in the fuel conditioning module to heat includes exposing the fuel to resistance heating, infrared heating, and / or induction heating.

23. The method according to any one of claims 17 to 22, further including injecting air or an oxygencontaining gas in the fuel conditioning module to induce partial oxidation reactions.

24. The method according to any one of claims 17 to 23, further including preheating the fuel using heat reclaimed from engine components associated with the combustor.

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