NOZZLE FOR FEEDING AIR AND LIQUID FUEL INTO A COMBUSTION CHAMBER, AND ENGINE

[0001]This application claims priority to German Patent Application 102024132232.2 filed Nov. 5, 2024, the entirety of which is incorporated by reference herein.

[0002]The invention relates to a nozzle for feeding air and liquid fuel into a combustion chamber, in particular of an engine of an aircraft, according to the preamble of Claim 1, and to an engine.

[0003]A nozzle of this kind, which, according to its principle of operation, belongs to the category of air-jet atomizer nozzles, is specified in DE 10 2017 218 529 A1. In this case, an annular fuel duct is arranged around a central air duct, and two radially offset annular air guide ducts are in turn arranged around the annular fuel duct. When the fuel emerges onto the film applicator surface, the fuel film is transported in the direction of the trailing edge by the passing air from the central air duct and, after flowing out between the central air flow and one of the outer air flows, is atomized into fine droplets.

[0004]Another nozzle of this kind is known from U.S. Pat. No. 9,423,137B2. In the case of this known nozzle for adding liquid fuel to a combustion chamber, there is a plurality of radially offset fuel ducts, via which fuel is added to different air ducts.

[0005]Other nozzles for feeding air and liquid fuel into a combustion chamber are known from US 2014/0241871 A1, US 2020/0141582 A1, US 2022/0099290 A1, US 2016/0047315 A1 and US 2010/0229556A1 .

[0006]Tests by means of high resolution flow simulations have shown that the process by which the fuel flows off the film applicator surface is in part subject to periodic fluctuations. These fluctuations consist, on the one hand, in the build-up and collapse of fuel waves due to the interaction with the air flowing over at the fuel outlet opening. In this way, large liquid filaments of flow can form as the fuel leaves the trailing edge, and, further downstream, these break down into relatively large droplets. On the other hand, fluctuations occur due to occupation of the film applicator surface by waves of fuel emerging from the fuel outlet opening. Owing to the fluctuations in the fuel mass flow and the resulting droplet size distribution, pressure fluctuations/thermoacoustics associated with the flame dynamics may occur, and there may be a negative effect on the formation of pollutants within the combustion chamber.

[0007]It is the underlying object of the invention to provide a nozzle for stable operation of a combustion chamber with low levels of pollutants, as well as an engine that can be operated in a stable manner with low levels of pollutants.

[0008]For the nozzle, the invention is achieved by the features of Claim 1, and for the engine by the features of Claim 10. In the case of the nozzle, it is envisaged that a length of the film applicator surface between the fuel outlet opening and the trailing edge is a factor of 5 to 6, preferably a factor of 5.5, times a height of the end portion of the fuel duct. The fuel duct is preferably of annularly encircling design, at least within the end portion. In the present context, height refers to the (possibly maximum) distance between a radially inner wall surface and a radially outer wall surface of the end portion, obtained orthogonally to a central longitudinal plane extending centrally between these two walls. The height within the end portion is preferably at least substantially constant in the direction of flow (e.g. apart from transitional portions, such as after the transition of the fuel duct from the axial portion to the end portion).

[0009]In particular, the nozzle is of at least substantially rotationally symmetrical design, wherein the length of the film applicator surface is preferably constant, forming an annular surface encircling the nozzle longitudinal axis.

[0010]The film applicator surface is arranged adjacent to the first air duct to enable an air flow flowing through the first air duct to flow over it, preferably in its entirety. The relatively long film applicator surface allows increased transfer of momentum from the air flow within the first air duct to the fuel film as compared with the prior art. The fuel film is subject to greater acceleration and reaches the trailing edge at a higher flow velocity (relative to the nozzle body). When it reaches the trailing edge, the fuel film has a smaller radial thickness. This contributes to the formation of the relatively small fuel ligaments when the fuel separates from the trailing edge, thereby reducing or preventing accumulation of fuel from the overall mass flow at a single outlet opening. Wave formation or fluctuations in the fuel mass flow are significantly reduced, this being associated with more uniform combustion with significantly increased stability and reduced pollutant emissions, especially reduced soot formation.

[0011]Another positive effect on fuel atomization is achieved if the film applicator surface is inclined axially-radially at an angle (in particular a constant angle) of between 5° and 15° to the nozzle longitudinal axis in such a way that it runs in the direction of the nozzle longitudinal axis in the direction of flow. As a result, the first air duct converges in the direction of flow in the region of the film applicator surface to form a kind of annular cone.

[0012]Provision is furthermore preferably made for the downstream end portion to be inclined axially-radially at an angle of between 25° and 35° to the nozzle longitudinal axis in such a way that it runs in the direction of the nozzle longitudinal axis in the direction of flow.

[0013]Provision is preferably made for the outlet area of the fuel outlet opening to be aligned orthogonally to the nozzle longitudinal axis, or orthogonally to a central longitudinal plane of the end portion, or between these two alignments. In this case, the outlet area extends between an outlet edge adjacent to the nozzle axis, optionally extending in the circumferential direction, and an optionally encircling line of transition to the film applicator surface. As a result, the radial outer side of the outlet opening is at the same position with respect to the nozzle longitudinal axis, or further downstream than the radial inner side of the outlet opening, but not upstream. As a result, the film applicator surface is arranged entirely axially at the level of and/or downstream of a nozzle main body delimiting the fuel duct radially on the inside, as a result of which the air flow flows over the fuel over a large area of the film applicator surface, in particular over the entire film applicator surface, during operation.

[0014]For a long-lived design that is advantageous in terms of flow and is nevertheless as stable as possible, a flank extending radially between an inner radius and an outer radius, aligned at least substantially orthogonally to the nozzle longitudinal axis, and upstream of the film applicator surface is arranged (radially) between the first air duct and the fuel duct, axially at the position of the fuel outlet opening, between the first air duct and the fuel outlet opening, said flank having a (radial) height of between 0.15 mm and 0.25 mm. The flank can also be of rounded or bevelled design. The inner radius thus corresponds to the innermost radial position of the flank, adjoining the inner air duct, and is arranged at a downstream end of the end portion and/or of the main body surrounding the first air duct. The inner radius preferably corresponds to the smallest radius of the air duct. The outer radius corresponds to the outermost radial position of the flank, adjoining the fuel duct, in particular the fuel outlet opening, radially on the inside.

[0015]In this context, the trailing edge is preferably positioned radially (that is to say with respect to the radial position) between the inner radius and the outer radius, i.e. R_i≤R (trailing edge)≤R_a. Thus, the conical profile of the first air duct within the portion of the film applicator surface does not lead to a cross-sectional constriction of the first air duct relative to the portion with the radius R_i.

[0016]In one preferred design variant, it is envisaged that a flank aligned at least substantially orthogonally to the nozzle longitudinal axis, which is downstream of the film applicator surface and which has a (radial) height of up to 0.2 mm, e.g. between 0.1 mm under 0.2 mm, is arranged axially at the position of the trailing edge, radially between the film applicator surface or the first air duct and the second air duct. In particular, the height is constant in the circumferential direction. In combination with the inward-directed end portion of the fuel duct, a trailing edge which is as sharp-edged as possible is thus advantageously formed, contributing to the formation of fuel ligaments that are as small as possible and/or to the reduction of fuel reservoir formation. The preferred height between 0.1 mm and 0.2 mm furthermore serves for a stable, long-lived design.

[0017]For an optimized flow field within the combustion chamber, two air ducts, within each of which a swirl generator is preferably arranged (generation of a flow with superposed tangential velocity component), are preferably arranged radially on the outside, in particular in an annularly encircling manner, around the fuel duct, said air ducts being offset radially relative to one another, e.g. being arranged coaxially with one another, at least in some section or sections.

[0018]In this context, the two air ducts preferably each have a downstream end portion for entry into the combustion chamber which is aligned axially-radially in the direction of the nozzle longitudinal axis. The end portions can be aligned at least substantially parallel to one another, for example. At least the inner, second air duct preferably has a steeper axial-radial alignment than the end portion of the fuel duct.

[0019]The swirling air flow passed through the two outer air ducts is directed radially inwards by means of the axially-radially aligned end portions, and comes together with the air flow from the first air duct at the downstream end of the film applicator surface. In this way, the fuel flow at the trailing edge at the downstream end of the film applicator surface is incorporated into two air flows and is broken up into fine droplets by these. In the embodiment with three air ducts, comprising two air ducts arranged radially outside the fuel duct, the air duct which is situated radially furthest towards the outside, also referred to as “dome air passage”, likewise imparts a swirl to the air flow if there is a swirl generator present, and, on account of the axially-radially aligned end portion, initially directs this flow radially inwards. This air flow has the effect and/or reinforces the effect that the flow consisting of air (from the first and second air ducts) and fuel (droplets) gives rise by virtue of its angular momentum to a pressure gradient as it flows into the combustion chamber, such that the air-fuel flow is pulled radially outwards, and a swirling hollow cone spray is thus generated.

[0020]The invention will be explained in more detail below on the basis of exemplary embodiments with reference to the drawings, in which:

[0021]FIG. 1 shows schematically in longitudinal section part of a nozzle for feeding air and liquid fuel into a combustion chamber in accordance with the prior art, having a (central) first air duct, a fuel duct and two outer air ducts,

[0022]FIG. 2 shows schematically in longitudinal section part of a nozzle according to the invention for feeding air and liquid fuel into a combustion chamber, having an extended film applicator surface inclined axially-radially inwards in the direction of flow, and

[0023]FIG. 3 shows schematically in longitudinal section part of the nozzle according to the invention shown in FIG. 2 without illustrating the two outer air ducts and a fuel flow.

[0024]FIG. 1 shows schematically part of a nozzle main body 10 of a nozzle for feeding air 13 and liquid fuel 18 into a combustion chamber 28 of an engine of an aircraft, with the fuel being atomized, as known from the prior art. The liquid fuel 18 is, in particular, kerosene or a kerosene-based fuel and/or a synthetic liquid fuel.

[0025]The nozzle main body 10 is aligned with a main body 30, in particular a rotationally symmetrical main body, along a nozzle longitudinal axis M. A first, in particular cylindrical, air duct 14, which is bounded circumferentially by the main body 30 and extends on the nozzle longitudinal axis M, at least in some section or sections, is provided. A swirl generator (not shown here) for imposing a swirl (velocity component in the circumferential direction) on the fraction of the air that flows through during operation is preferably arranged in the first air duct 14. The first air duct 14 opens into the combustion chamber 28, in particular with an exclusively axial direction component.

[0026]The nozzle main body 10 has a fuel duct 16 in the form of a ring radially encircling the first air duct 14. The radial inner wall of the fuel duct 16 is formed by the main body 30, while the radial outer wall is formed by an outer fuel duct wall 26. The fuel duct 16 has an axial portion 161 aligned coaxially with the nozzle longitudinal axis M, and adjoining this in the direction of flow, a downstream end portion 162, which is aligned axially-radially inwards in the direction of the nozzle longitudinal axis M and opens into a fuel outlet opening 24. The fuel outlet opening 24 or the outlet area thereof is aligned so as to extend substantially exclusively axially with respect to the nozzle longitudinal axis M. Moreover, by way of example, the fuel outlet opening 24 is arranged in a manner offset radially outwards with respect to the inner wall of the first air duct 14. An inward offset would also be possible.

[0027]Downstream of the fuel outlet opening 24, said opening is adjoined by a film applicator surface 20, on the downstream end of which a trailing edge 22 is arranged. The film applicator surface 20 is aligned exclusively axially with respect to the nozzle longitudinal axis M, and therefore forms an encircling annular cylinder segment aligned around the nozzle longitudinal axis M.

[0028]The fuel outlet opening 24 and the film applicator surface 20 are arranged, in particular, at the downstream end of the first air duct 14 to enable air flowing through the first air duct 14 to flow over them.

[0029]Encircling the fuel duct 16 radially in an annular manner, the nozzle main body 10 preferably has an outer air duct arrangement 12 comprising two air ducts, a second air duct 121 and a radially outermost third air duct 122, arranged radially offset with respect to one another. Swirl generators 123, 124 are preferably arranged in the air ducts 121, 122. The air ducts 121, 122 each have a downstream end portion for entry into the combustion chamber 28 which is aligned axially-radially in the direction of the nozzle longitudinal axis M. In the present case, by way of example, the end portions run substantially parallel to one another and/or to the end portion 162 of the fuel duct 16. Some other alignment of the end portions for selectively influencing the flow pattern formed in the combustion chamber 28 is also possible.

[0030]During operation, air 13 is passed through the air ducts 14, 121, 122, of which there are three here by way of example. The liquid fuel 18 is passed through the at least one fuel duct 16 to the preferably annular fuel outlet opening 24 and flows onto the film applicator surface 20, in particular directly downstream of the fuel outlet opening 24. The air 13 flowing through the first air duct 14, which is, in particular, subject to swirl, flows along the nozzle longitudinal axis M and, shortly before flowing out of the nozzle into the combustion chamber 28, sweeps across the film applicator surface 20. As a result, the fuel flow flowing over the film applicator surface 20 is transported. Shear stresses applied by the air 13 induce (small-scale) flow instabilities in the fuel flow and entrain individual fuel droplets out of the film.

[0031]The swirling air flow flowing through the second air duct 121 and the third air duct 122 is directed radially inwards by means of the axially-radially aligned end portions, and comes together with the air flow from the first air duct 14 at the downstream end of the film applicator surface 20. In this way, the fuel flow at the trailing edge 22 at the end of the film applicator surface 20 is incorporated into two air flows and is broken up into fine droplets by these. In the embodiment with three air ducts, the third air duct 122, which is situated radially furthest towards the outside, also referred to as a “dome air passage”, likewise imparts a swirl to the air flow and, on account of the axially-radially aligned end portion, initially directs this flow radially inwards. By virtue of its angular momentum, this air flow brings about a pressure gradient such that the flow consisting of the air 13 and the fuel 18 (droplets) is pulled radially outwards as it flows into the combustion chamber 28, and a swirling hollow cone spray is generated.

[0032]Tests on the fuel flow at the fuel outlet opening 24 have shown that the fuel 18 flowing away from the film applicator surface 20 is subject to fluctuations. These fluctuations consist, on the one hand, in that, on account of the interaction with the air flowing over at the fuel outlet opening 24, fuel waves may build up upstream of the film applicator surface 20, and these migrate downstream and collapse over the film applicator surface 20. In this way, large filaments of flow can form downstream of the trailing edge 22, and, further downstream, these break down into relatively large droplets. On the other hand, there are fluctuations in occupation of the film applicator surface 20 by waves of fuel 18 emerging from the fuel outlet opening 24. As a result, fuel mass flows of different magnitudes leave the film applicator surface 20 at different times in a partially periodically repeated sequence.

[0033]Owing to the fluctuations in the fuel mass flow and the resulting droplet size distribution, pressure fluctuations/thermoacoustics associated with the flame dynamics may occur, and there may be a negative effect on the formation of pollutants within the combustion chamber 28.

[0034]To avoid such fluctuations of the fuel mass flow as it flows away from the film applicator surface 20, a nozzle of the kind illustrated schematically by way of example in a longitudinal section in FIG. 2 and FIG. 3 is proposed. Apart from the differences essential to the invention, as explained below, the part illustrated in FIG. 2 corresponds to the part of the nozzle illustrated in FIG. 1. The part illustrated in FIG. 3 essentially shows the fuel duct 16 with part of the main body 30 and the outer fuel channel wall 26 as well as the film applicator surface 20 and the trailing edge 22.

[0035]In the present case, the design of the nozzle as regards the air ducts 14, 121 and 122 corresponds substantially to the design shown in FIG. 1.

[0036]In contrast to the nozzle shown in FIG. 1, the nozzle according to the invention shown in FIG. 2 and FIG. 3 has a film applicator surface 20 which extends over a significantly longer length (being longer by a factor of 1.5 to 4, for example), which extends downstream from the outer edge of the fuel outlet opening 24 as far as the trailing edge 22.

[0037]Relative dimensions of the film applicator surface can be gleaned from FIG. 3: a length L of the film applicator surface 20 between the fuel outlet opening 24 and the trailing edge 22 is between a factor of 5 and 6, preferably a factor of 5.5, times a height H of the end portion 162 of the fuel duct 16. In the present case, height H refers to the distance between a radially inner wall surface 163 and a radially outer wall surface 164 within the end portion 162, obtained orthogonally to a central longitudinal plane E extending centrally between these two wall surfaces 163, 164. The height H is preferably at least substantially constant in the direction of flow within the end portion 162 (e.g. after a transition from the axial portion 161).

[0038]In addition, in particular, the film applicator surface 20 is inclined axially-radially at an angle α of between 5° and 15° to the nozzle longitudinal axis M in such a way that it runs in the direction of the nozzle longitudinal axis in the direction of flow. As a result, the first air duct 14 is convergent in the direction of flow, in the manner of an annular cone, in the axial portion of the film applicator surface 20. Here, the angle α forms half the opening angle of the cone. Here, the angle α is, in particular, shallower than an axial-radial inclination of the end portion of the second air duct 121, and therefore an angle that is as acute as possible, with a trailing edge 22 that is as sharp-edged as possible relative to the outer air duct arrangement 112, is formed.

[0039]The downstream end portion 162 runs in the direction of the nozzle longitudinal axis M in the direction of flow, wherein the end portion 162 is inclined axially-radially at an angle β of between 25° and 35° to the nozzle longitudinal axis M.

[0040]At the downstream end of the end portion 162, the fuel outlet opening 24 extends in an outlet area between the outer wall surface 164 and the inner wall surface 163. With respect to the outer wall surface 164, the downstream end of the end portion 162 is arranged at an axial position P₂ at which the outer wall surface 164 with the steeper angle of incidence, angle β, merges into the film applicator surface 20 with the shallower angle of incidence, angle α (line of transition to the film applicator surface). With respect to the inner wall surface 163, the downstream end of the end portion 162 is arranged at an axial position P₁ at which the inner wall surface 163 merges into a flank 25 on the downstream end of the main body 30, said flank being aligned substantially orthogonally to the nozzle longitudinal axis M (outlet edge adjacent to the nozzle axis).

[0041]Here, the fuel outlet opening 24 or the outlet area between the axial position P₁ and P₂ is, in particular, aligned as far as possible orthogonally to the nozzle longitudinal axis M or, as shown in FIG. 3, is inclined somewhat forwards in the direction of flow or towards the nozzle longitudinal axis M on the radial outer side (axial position P₂), wherein the axial position P₂ is arranged downstream of the axial position P₁. The inclination is maximal such that the fuel outlet opening 24 is aligned orthogonally to the central longitudinal plane E of the end portion 162. In FIG. 3, the alignment is between the alignment orthogonal to the nozzle longitudinal axis M and the alignment orthogonal to the central longitudinal plane E.

[0042]The downstream front flank 25 of the main body 30 is arranged upstream of the film applicator surface 20 on the downstream end of the main body 30, substantially at the axial position P₁. The flank 25 is preferably aligned orthogonally to the nozzle longitudinal axis M but may also be of inclined and/or rounded design. The flank 25 extends radially between an inner radius R_i and an outer radius R_a with respect to the nozzle longitudinal axis M. For a long-lived design which is advantageous in terms of flow and is nevertheless as stable as possible, the flank 25 preferably has a radial height of between 0.15 mm and 0.25 mm.

[0043]In the portion upstream of the flank 25, the air duct 14 has the inner radius R_i, which preferably forms the smallest radius within the air duct. A radius R at the radial position of the trailing edge 22 at the downstream end of the film applicator surface 20 is preferably between the inner radius R_i and the outer radius R_a (where R_i≤R≤R_a). In this way, the trailing edge 22 is positioned radially between the inner radius R_i and the outer radius R_a. Consequently, the conical portion of the first air duct 14 in the region of the film applicator surface 20 does not include the narrowest flow cross section and/or the smallest radius within the first air duct 14.

[0044]A downstream flank 23 aligned substantially orthogonally to the nozzle longitudinal axis M is arranged at the axial position of the trailing edge 22, radially adjoining the trailing edge 22 and the second air duct 121 (cf. FIG. 2). For a long-lived design that is advantageous in terms of flow and is nevertheless as stable as possible, the flank 23 preferably has a radial height of between 0.1 mm and 0.2 mm.

[0045]As extensive studies by the inventors have shown, design features of the nozzle according to the invention, especially when combined, bring about significantly improved atomization of the fuel, wherein the formation of large ligaments when the fuel separates from the trailing edge 22 is largely or virtually completely prevented. Large ligaments break down into large droplets during the secondary atomization that follows downstream of the nozzle. The suppression of ligament formation leads to the formation of a droplet spectrum with a significantly more homogeneous droplet size (narrower size distribution), and to suppression of periodically timed fluctuations within the size distribution. On the one hand, the film applicator surface 20 extending over a relatively long length and preferably tapering conically allows increased transfer of momentum from the air flow within the first air duct 14 to the fuel film as compared with the prior art. The fuel film is subject to greater acceleration and reaches the trailing edge 22 at a higher flow velocity (relative to the nozzle body). When it reaches the trailing edge 22, the fuel film has a smaller radial thickness. This contributes to the formation of the relatively small fuel ligaments when the fuel separates from the trailing edge 22. At the same time, owing to the small radial dimensions of the flank 23 at the position of the trailing edge 22, the first air duct 14 essentially merges with the outer air duct arrangement 12 downstream of the film applicator surface 20. As a result, the effect known from the prior art of reservoir formation due to adhesion of fuel to the orthogonal flank 23 is reduced.

List of Reference Signs