Nozzle for supplying air and liquid fuel to a combustion chamber and engine

Abstract

The invention relates to a nozzle for supplying air and liquid fuel to a combustion chamber (28), in particular of an aircraft engine, with a nozzle body (10) aligned along a nozzle longitudinal axis (M), in which the following are arranged: - at least one first air channel (14) extending on and / or around the nozzle longitudinal axis (M), - at least one fuel channel (16) arranged radially outside, in particular annularly, around the first air channel (14), which has an axially radially extending, downstream end section (162) extending in the direction of flow towards the nozzle longitudinal axis (M), and - at least one second air channel (121) arranged radially outside, in particular annularly, around the fuel channel (16), wherein the fuel channel (16) opens with a fuel outlet opening (24) on an adjoining, at least substantially axially oriented film laying surface (20) with a downstream trailing edge (22).wherein the film laying surface (20) delimits the first air channel (14) downstream. Fuel atomization is improved by the fact that a length (L) of the film laying surface (20), between the fuel outlet opening (24) and the outflow edge (22), is between a factor of 5 and 6, preferably a factor of 5.5, times a height (H) of the end section (162) of the fuel channel (16) (Fig. 2).

Description

[0001] The invention relates to a nozzle for supplying air and liquid fuel into a combustion chamber, in particular of an aircraft engine, according to the preamble of claim 1, and to an engine.

[0002] Such a nozzle, which according to its operating principle is classified as an air jet atomizing nozzle, is described in DE 10 2017 218 529 A1. It comprises an annular fuel channel surrounding a central air channel, and around this, in turn, two radially offset, annular air guide channels. When the fuel exits onto the film-laying surface, the fuel film is transported by the air flowing past the central air channel towards the trailing edge and, after flowing away, is atomized into fine droplets between the central airflow and one of the outer airflows.

[0003] Another nozzle of this type is known from US 9,423,137 B2. This known nozzle for adding liquid fuel to a combustion chamber has several radially offset fuel channels through which fuel is added to different air channels.

[0004] Further nozzles for supplying 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 / 0229556 A1.

[0005] Investigations using high-resolution flow simulations have shown that the fuel flow from the film-laying surface is subject to fluctuations, some of which are periodic. These fluctuations consist, firstly, of the formation and collapse of fuel waves due to the interaction with the overflowing air at the fuel outlet. In this way, large liquid streamlines can form as the fuel leaves the outflow edge, which then break up into relatively large droplets further downstream. Secondly, fluctuations arise from the wave-like coating of the film-laying surface with fuel exiting the fuel outlet. As a result of the fluctuations in the fuel mass flow and the resulting droplet size distribution, pressure fluctuations / thermoacoustics related to the flame dynamics can occur, negatively impacting pollutant formation within the combustion chamber.

[0006] The invention is based on the objective of providing a nozzle for stable and low-emission operation of a combustion chamber, as well as a stable and low-emission engine.

[0007] The invention is solved for the nozzle with the features of claim 1 and for the engine with the features of claim 10. In the nozzle, the length of the film-laying surface between the fuel outlet opening and the downstream edge is a factor of 5 to 6, preferably a factor of 5.5, times the height of the end section of the fuel channel. The fuel channel is preferably designed to be annular, at least within the end section. The height is defined here as the (possibly maximum) distance between a radially inner wall surface and a radially outer wall surface of the end section, which is orthogonal to a longitudinal central surface running between these two walls.The height within the end section is preferably at least substantially constant in the direction of flow (for example, apart from transition sections, such as after the transition of the fuel channel from the axial section to the end section).

[0008] The nozzle is in particular designed to be at least essentially rotationally symmetrical, wherein the length of the film laying surface is preferably constant, forming a ring surface circumferential around the longitudinal axis of the nozzle.

[0009] The film-laying surface is preferably arranged completely adjacent to the first air channel, allowing it to be overlaid by an airflow passing through the first air channel. The comparatively long film-laying surface enables a higher momentum transfer of the airflow within the first air channel to the fuel film compared to the prior art. The fuel film is accelerated more strongly and reaches the trailing edge with a higher flow velocity (relative to the nozzle body). Upon reaching the trailing edge, the fuel film has a reduced radial thickness. This contributes to the formation of smaller fuel ligaments when the fuel detaches from the trailing edge, thereby reducing or preventing fuel accumulation from the total mass flow at a single outlet opening. Ripple formation or...Fluctuations in fuel mass flow are significantly reduced, resulting in more even combustion with significantly increased stability and reduced pollutant emissions, especially reduced soot formation.

[0010] Furthermore, fuel atomization is positively affected if the film-laying surface is inclined axially-radially at an angle (especially a constant one) between 5° and 15° to the nozzle's longitudinal axis, such that it runs in the direction of the flow along the nozzle's longitudinal axis. In this way, the first air channel in the area of ​​the film-laying surface converges in the direction of the flow, forming a kind of annular cone.

[0011] Preferably, it is further provided that the downstream end section is inclined axially-radially at an angle between 25° and 35° relative to the nozzle longitudinal axis, such that it runs in the direction of flow towards the nozzle longitudinal axis.

[0012] Preferably, the outlet surface of the fuel outlet is oriented orthogonally to the nozzle's longitudinal axis, or orthogonally to a central longitudinal surface of the end section, or between these two orientations. The outlet surface extends between an outlet edge on the nozzle axis side, optionally extending circumferentially, and a transition line to the film-laying surface, optionally circumferential. In this way, the radial outer surface of the outlet is located at the same position as, or further downstream of, the radial inner surface of the outlet with respect to the nozzle's longitudinal axis, but not upstream. Thus, the film-laying surface is arranged completely axially at the level of and / or downstream of a base body of the nozzle that radially delimits the fuel channel on its inner side, so that during operation, the fuel is flowed over a large area of ​​the film-laying surface, in particular over the entire film-laying surface, by the airflow.

[0013] For a streamlined yet stable and durable design, a radially extending flank, oriented at least substantially orthogonal to the nozzle's longitudinal axis and with respect to the film laying surface, is arranged axially between the first air channel and the fuel outlet opening, at the fuel outlet opening. This flank has a radial height between 0.15 mm and 0.25 mm and has an inner radius between an inner radius and an outer radius. The flank can also be rounded or chamfered. The inner radius corresponds to the innermost radial position of the flank, adjacent to the inner air channel, and is located at a downstream end of the end section and / or the base body surrounding the first air channel. Preferably, the inner radius corresponds to the smallest radius of the air channel.The outer radius corresponds to the outermost radial position of the flank, radially adjacent to the fuel channel on the inside, in particular to the fuel outlet opening.

[0014] Preferably, in this context, the outflow edge is positioned radially (i.e., with respect to its radial position) between the inner radius and the outer radius, i.e., Ri ≤ R(outflow edge) ≤ Ra. Thus, the conical shape of the first air channel within the section of the film laying surface does not lead to a cross-sectional narrowing of the first air channel compared to the section with radius Ri.

[0015] In a preferred embodiment, a flank is arranged axially at the position of the outflow edge, radially between the film laying surface or the first air channel and the second air channel. This flank is oriented at least substantially orthogonally to the nozzle's longitudinal axis and is located downstream of the film laying surface. This flank has a (radial) height of up to a maximum of 0.2 mm, e.g., between 0.1 mm and 0.2 mm. The height is particularly constant in the direction of rotation. In conjunction with the inwardly directed end section of the fuel channel, this advantageously creates a sharp-edged outflow edge, which contributes to the formation of minimal fuel ligaments and / or the reduction of fuel reservoir formation. The preferred height of between 0.1 mm and 0.2 mm also ensures a stable and durable design.

[0016] For an optimized flow field within the combustion chamber, two radially offset air channels, e.g. at least partially coaxial to each other, are preferably arranged radially outside, in particular in a ring-shaped configuration, around the fuel channel, within which a swirl generator (generation of a flow with a superimposed tangential velocity component) is preferably arranged.

[0017] In this context, the two air channels preferably each have a downstream end section leading to the combustion chamber, which is oriented axially-radially in the direction of the nozzle's longitudinal axis. The end sections can, for example, be aligned at least substantially parallel to each other. Preferably, at least the inner, second air channel has a steeper axial-radial orientation than the end section of the fuel channel.

[0018] The swirling airflow, guided through the two outer air channels, is directed radially inwards by the axially and radially oriented end sections, where it merges with the airflow from the first air channel at the downstream end of the film laying surface. In this way, the fuel flow at the trailing edge at the downstream end of the film laying surface is embedded in two airflows and broken up into fine droplets by them. In the version with three air channels, comprising two radially outside the fuel channel, the outermost air channel, also known as the "dome air passage," also imparts a swirl to the airflow when a swirl generator is present and, due to its axially and radially oriented end section, initially directs it radially inwards.This airflow causes and / or intensifies the flow of air (from the first and second air channels) and fuel (droplets) as they enter the combustion chamber, creating a pressure gradient due to their angular momentum, such that the air-fuel flow is pulled radially outwards, thus generating a twisted hollow cone spray.

[0019] The invention will now be explained in more detail using exemplary embodiments and with reference to the drawings. The drawings show: Fig. 1 shows a schematic longitudinal section of a nozzle for supplying air and liquid fuel to a combustion chamber according to the prior art, with a (central) first air channel, a fuel channel, and two outer air channels; Fig. 2 shows a schematic longitudinal section of a nozzle according to the invention for supplying air and liquid fuel to a combustion chamber, with an extended film-laying surface inclined axially-radially inwards in the flow direction; and Fig. 3 shows a part of the nozzle according to the invention. Fig. 2 schematic longitudinal section without showing the two outer air channels and fuel flow.

[0020] Fig. 1 Figure 1 schematically shows a portion of a nozzle body 10 of a nozzle for supplying air 13 and liquid fuel 18 under fuel atomization into a combustion chamber 28 of an aircraft engine, 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.

[0021] The main nozzle body 10 is aligned with a base body 30, which is in particular rotationally symmetrical, along a nozzle longitudinal axis M. A first air channel 14, which extends at least partially along the nozzle longitudinal axis M and is in particular cylindrical, is circumferentially bounded by the base body 30. Preferably, a swirl generator for imparting swirl (velocity component in the circumferential direction) to the air flowing through it during operation is arranged in the first air channel 14 (not shown here). The first air channel 14 opens into the combustion chamber 28, in particular with an exclusively axial directional component.

[0022] Radially surrounding the first air channel 14 in a ring-like fashion, the main nozzle body 10 has a fuel channel 16. The radial inner wall of the fuel channel 16 is formed by the base body 30, and the radial outer wall by an outer fuel channel wall 26. The fuel channel 16 has an axial section 161, aligned coaxially with the nozzle's longitudinal axis M, and subsequently, in the flow direction, an axially radially inwardly oriented, downstream end section 162, which opens into a fuel outlet opening 24. The fuel outlet opening 24, or rather its outlet surface, is oriented essentially only axially with respect to the nozzle's longitudinal axis M. Furthermore, the fuel outlet opening 24 is, by way of example, arranged radially outwardly offset from the inner wall of the first air channel 14. An inward offset would also be possible.

[0023] Downstream of the fuel outlet opening 24, a film laying surface 20 adjoins it, at the downstream end of which a trailing edge 22 is arranged. The film laying surface 20 is aligned exclusively axially with respect to the nozzle longitudinal axis M, so that it forms a circumferentially oriented annular cylindrical section around the nozzle longitudinal axis M.

[0024] The fuel outlet opening 24 and the film laying surface 20 are arranged in particular at the downstream end of the first air duct 14, for flow over with air flowing through the first air duct 14.

[0025] Radially encircling the fuel channel 16, the main nozzle body 10 preferably has an outer air channel arrangement 12 with two radially offset air channels, a second air channel 121, and a radially outermost, third air channel 122. Swirl generators 123, 124 are preferably arranged in the air channels 121, 122. The air channels 121, 122 each have a downstream end section leading to the opening in the combustion chamber 28, which is oriented axially-radially inwards, in the direction of the nozzle's longitudinal axis M. In this example, the end sections run essentially parallel to each other and / or to the end section 162 of the fuel channel 16. Other orientations of the end sections are also possible in order to selectively influence the flow pattern that develops in the combustion chamber 28.

[0026] During operation, air 13 is guided through the three air channels 14, 121, 122 shown here as examples. The liquid fuel 18 is guided through the at least one fuel channel 16 to the preferably annular fuel outlet 24 and flows, particularly directly downstream of the fuel outlet 24, onto the film laying surface 20. The air 13 flowing through the first air channel 14, which is particularly swirling, flows along the nozzle longitudinal axis M and passes over the film laying surface 20 shortly before exiting the nozzle into the combustion chamber 28. This transports the fuel flow over the film laying surface 20. Shear stresses induced by the air 13 cause (small-scale) flow instabilities in the fuel flow and tear individual fuel droplets from the film.

[0027] The swirling airflow passing through the second air channel 121 and third air channel 122 is guided radially inwards by the axially and radially oriented end sections, where it meets the airflow from the first air channel 14 at the downstream end of the film laying surface 20. In this way, the fuel flow at the trailing edge 22 at the end of the film laying surface 20 is embedded in two airflows and broken up into fine droplets by them. In the three-air-channel configuration, the radially outermost, third air channel 122, also referred to as the "dome air passage," also imparts a swirl to the airflow and, due to its axially and radially oriented end section, initially guides it radially inwards.This airflow, through its angular momentum, creates a pressure gradient such that the flow of air 13 and fuel 18 (droplets) is drawn radially outwards when entering the combustion chamber 28, generating a twisted hollow cone spray.

[0028] Investigations of the fuel flow at the fuel outlet 24 have revealed that the fuel 18 flowing from the film laying surface 20 is subject to fluctuations. These fluctuations consist, firstly, of fuel waves forming upstream of the film laying surface 20 due to the interaction with the overlying air at the fuel outlet 24. These waves then propagate downstream and collapse over the film laying surface 20. In this way, large streamlines can form downstream of the trailing edge 22, which further downstream break up into relatively large droplets. Secondly, fluctuations also occur in the wave-like coating of the film laying surface 20 with fuel 18 exiting the fuel outlet 24. As a result, fuel mass flows of varying sizes leave the film laying surface 20 at different times in a partially periodic, repeating sequence.

[0029] As a result of fluctuations in the fuel mass flow and the resulting droplet size distribution, pressure fluctuations / thermoacoustics related to the flame dynamics can occur and the formation of pollutants within the combustion chamber 28 can be negatively affected.

[0030] To avoid such fluctuations in the fuel mass flow when flowing from the film laying surface 20, a nozzle is proposed, as exemplified in Fig. 2 and Fig. 3 schematically depicted in a longitudinal section. The in Fig. 2 Apart from the differences essential to the invention, as explained below, the depicted part corresponds to the one in Fig. 1 depicted part of the nozzle. The part shown in Fig. 3 The depicted part essentially shows the fuel channel 16 with part of the base body 30 and the outer fuel channel wall 26, as well as the film laying surface 20 and the outflow edge 22.

[0031] The design of the nozzle with respect to the air channels 14, 121 and 122 essentially corresponds to the design as described in Fig. 1 shown.

[0032] Unlike the one in Fig. 1 The nozzle shown has the in Fig. 2 and Fig. 3 The nozzle shown according to the invention has a significantly longer (e.g. by a factor of 1.5 to 4 longer) film laying surface 20, which extends from the outer edge of the fuel outlet opening 24 downstream to the outflow edge 22.

[0033] Relative dimensions of the film laying area are derived from Fig. 3 Removable: The length L of the film laying surface 20 between the fuel outlet opening 24 and the outflow edge 22 is between a factor of 5 and 6, preferably a factor of 5.5, times the height H of the end section 162 of the fuel channel 16. In this context, height H is defined as the distance between a radially inner wall surface 163 and a radially outer wall surface 164 within the end section 162, which is orthogonal to a central longitudinal surface E running between these two wall surfaces 163, 164. The height H is preferably constant in the flow direction within the end section 162, at least substantially (for example, after a transition from the axial section 161).

[0034] Furthermore, the film laying surface 20 is inclined axially-radially at an angle α between 5° and 15° relative to the nozzle longitudinal axis M such that it runs in the direction of flow along the nozzle longitudinal axis. In this way, the first air channel 14 in the axial section of the film laying surface 20 is designed in a conical shape, converting in the direction of flow. The angle α is half the opening angle of the cone. The angle α is particularly shallower than the axial-radial inclination of the end section of the second air channel 121, so that the most acute angle possible is formed, with the sharpest possible trailing edge 22 relative to the outer air channel arrangement 112.

[0035] The downstream end section 162 extends in the flow direction towards the nozzle longitudinal axis M, wherein the end section 162 is inclined axially-radially at an angle β between 25° and 35° relative to the nozzle longitudinal axis M.

[0036] At the downstream end of the end section 162, the fuel outlet opening 24 extends in an outlet surface between the outer wall surface 164 and the inner wall surface 163. The downstream end of the end section 162 is arranged at an axial position P 2 with respect to the outer wall surface 164, at which the outer wall surface 164, with the steeper angle, transitions at an angle β into the film laying surface 20, with the shallower angle, at an angle α (transition line to the film laying surface). The downstream end of the end section 162 with respect to the inner wall surface 163 is arranged at an axial position P 1, at which the inner wall surface 163 transitions into a flank 25 oriented substantially orthogonally to the nozzle longitudinal axis M at the downstream end of the base body 30 (nozzle axis exit edge).

[0037] The fuel outlet opening 24 or the outlet surface between the axial positions P1 and P2 is, in particular, aligned as orthogonally as possible to the nozzle longitudinal axis M or, as in Fig. 3 As shown, the radial outer side (axial position P2) is inclined slightly forward in the flow direction or towards the nozzle longitudinal axis M, with the axial position P2 being located downstream of the axial position P1. The inclination is maximal such that the fuel outlet opening 24 is aligned orthogonally to the central longitudinal surface E of the end section 162. Fig. 3 is the alignment between the alignment orthogonal to the nozzle longitudinal axis M and the alignment orthogonal to the central longitudinal surface E.

[0038] The downstream, leading flank 25 of the base body 30 is arranged upstream of the film laying surface 20 at the downstream end of the base body 30, essentially at the axial position P1. Preferably, the flank 25 is oriented orthogonally to the nozzle longitudinal axis M, but it can also be inclined and / or rounded. The flank 25 extends radially between an inner radius Ri and an outer radius Ra with respect to the nozzle longitudinal axis M. For a flow-optimized yet as stable and durable a design as possible, the flank 25 preferably has a radial height between 0.15 mm and 0.25 mm.

[0039] In the section upstream of flank 25, the air duct 14 has an inner radius Ri, 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 laying surface 20 preferably lies between the inner radius Ri and the outer radius Ra (with Ri ≤ Ra ≤ Ra). In this way, the trailing edge 22 is positioned radially between the inner radius Ri and the outer radius Ra. The conical section of the first air duct 14 in the region of the film laying surface 20 therefore does not comprise the narrowest flow cross-section and / or the smallest radius within the first air duct 14.

[0040] The axial position of the outflow edge 22 is radially adjacent to the outflow edge 22 and the second air duct 121 (cf. Fig. 2 A flank 23 is arranged downstream, oriented essentially orthogonally to the nozzle longitudinal axis M. For a flow-optimized yet stable and durable design, the flank 23 preferably has a radial height between 0.1 mm and 0.2 mm.

[0041] As extensive studies by the inventors have shown, the design features of the nozzle according to the invention, particularly in combination, result in significantly improved fuel atomization, whereby the formation of large ligaments when the fuel detaches from the trailing edge 22 is largely or practically completely prevented. Large ligaments break down into large droplets in the secondary atomization 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), as well as to the suppression of time-periodic fluctuations within the size distribution. On the one hand, the comparatively long and preferably conically tapered film-laying surface 20 enables an increased momentum transfer of the airflow within the first air channel 14 to the fuel film compared to the prior art.The fuel film is accelerated more strongly and reaches the trailing edge 22 with a higher flow velocity (relative to the nozzle body). Upon reaching the trailing edge 22, the fuel film has a smaller radial thickness. This contributes to the formation of smaller fuel ligaments when the fuel detaches from the trailing edge 22. At the same time, due to the small radial dimensions of the flank 23 at the position of the trailing edge 22, the first air channel 14 downstream of the film-laying surface 20 essentially merges with the outer air channel arrangement 12. This reduces the previously known effect of reservoir formation through fuel adhesion to the orthogonal flank 23. Bezugszeichenliste

[0042] 10 Nozzle main body 12 Outer air duct arrangement 121 Second air duct 122 Third air duct 123 Inner swirl generator 124 Outer swirl generator 13 Air 14 First air duct 141 Wall 16 Fuel channel 161 Axial section 162 End section 163 Inner wall surface 164 Outer wall surface 18 Fuel 20 Film laying surface 22 Outflow edge 23 Downstream flank 24 Outlet opening 25 Upstream flank 26 Outer fuel channel wall 28 Combustion chamber 30 Base body H Height L Length M Nozzle longitudinal axis E Central longitudinal surface P1 Axial position P2 Axial position Ri Inner radius Ra Outer radius RRadius

Claims

1. Nozzle for supplying air and liquid fuel to a combustion chamber (28), in particular of an aircraft engine, with a nozzle body (10) aligned along a nozzle longitudinal axis (M), in which the following are arranged: - at least one first air channel (14) extending on and / or around the nozzle longitudinal axis (M), - at least one fuel channel (16) arranged radially outside, in particular annularly, around the first air channel (14), which has an axially radially extending, downstream end section (162) extending in the direction of flow towards the nozzle longitudinal axis (M), and - at least one second air channel (121) arranged radially outside, in particular annularly, around the fuel channel (16), wherein the fuel channel (16) opens with a fuel outlet opening (24) on an adjoining, at least substantially axially oriented film laying surface (20) with a downstream trailing edge (22),wherein the film laying surface (20) delimits the first air duct (14) downstream, characterized by that a length (L) of the film laying surface (20), between the fuel outlet opening (24) and the outflow edge (22), is between a factor of 5 and 6, preferably a factor of 5.5, times a height (H) of the end section (162) of the fuel channel (16), wherein axially at the position of the fuel outlet opening (24) between the first air channel (14) and the fuel outlet opening (24) a radially extending between an inner radius (R i ) and an outer radius (R a ) extending, at least substantially orthogonal to the nozzle longitudinal axis (M), upstream flank (25) with respect to the film laying surface (20) is arranged between the first air channel (14) and the fuel channel (16), which has a height between 0.15 mm and 0.25 mm, wherein the outflow edge (22) is radially between the inner radius (R i ) and the outer radius (R a) is positioned.

2. Nozzle according to one of the preceding claims, characterized by that the film laying surface (20) is inclined axially-radially at an angle (α) between 5° and 15° to the nozzle longitudinal axis (M) such that it runs in the direction of flow in the direction of the nozzle longitudinal axis (M).

3. Nozzle according to one of the preceding claims, characterized by that the downstream end section (162) is inclined axially-radially at an angle (β) between 25° and 35° to the nozzle longitudinal axis (M) such that it runs in the direction of flow towards the nozzle longitudinal axis (M).

4. Nozzle according to one of the preceding claims, characterized by that the outlet surface of the fuel outlet opening (24) is aligned orthogonally to the nozzle longitudinal axis (M) or orthogonally to a central longitudinal surface (E) of the end section (162) or between these two orientations.

5. Nozzle according to one of the preceding claims, characterized by that axially at the position of the outflow edge (22) a flank (23) is arranged which is at least substantially orthogonal to the nozzle longitudinal axis (M) and downstream of the film laying surface (20), and which has a height of up to a maximum of 0.2 mm, e.g. between 0.1 mm and 0.2 mm.

6. Nozzle according to one of the preceding claims, characterized by that radially outside, in particular in a ring-shaped circumferential manner, around the fuel channel (16) two radially offset air channels (121, 122), e.g. at least partially coaxial to each other, are arranged, within which preferably a swirl generator (123, 124) is arranged.

7. Nozzle according to claim 6, characterized by thatthe two air channels (121, 122) each have a downstream end section leading to the opening into the combustion chamber (30), which is aligned axially-radially in the direction of the nozzle longitudinal axis (M).

8. Engine with at least one nozzle according to one of the preceding claims.

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