US20160153662A1

US20160153662A1 - Annular deflection wall for a turbomachine combustion chamber injection system providing a wide fuel atomization zone

Info

Publication number: US20160153662A1
Application number: US14/950,518
Authority: US
Inventors: Alain Cayre; Yoann Mery
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2014-11-28
Filing date: 2015-11-24
Publication date: 2016-06-02
Also published as: GB201521049D0; FR3029271B1; GB2534668A; FR3029271A1

Abstract

A deflection wall known as <<venturi>> is disclosed to improve the air fuel mix within an injection system installed in a turbomachine combustion chamber, having a downstream edge formed by the repetition of a pattern extending on each side of a virtual circle and formed from a plurality of bosses each of which is centred relative to a corresponding plane inclined by an angle α from a corresponding median axial plane of the annular deflection wall passing through a corresponding end of the downstream edge of the annular deflection wall at the boss considered.

Description

TECHNICAL DOMAIN

This invention relates to the domain of turbomachines for aircraft and more particularly relates to an annular deflection wall of the type currently known as <<venturi>>, to form part of a fuel and air injection system in a combustion chamber within a turbomachine.

STATE OF PRIOR ART

FIG. 1 appended illustrates a turbomachine 10 for an aircraft of a known type, for example a twin spool turbojet comprising in general a fan 12 that will draw in an airflow dividing downstream from the fan into a core engine flow supplying the core of the turbomachine and a fan flow bypassing this core. The turbomachine comprises basically a low pressure compressor 14, a high pressure compressor 16, a combustion chamber 18, a high pressure turbine 20 and a low pressure turbine 22. The turbomachine is surrounded by a nacelle 24 surrounding the flow space 26 of the fan flow. The turbomachine rotors are installed free to rotate about a longitudinal axis 28 of the turbomachine.
FIG. 2 shows the combustion chamber 18 of the turbomachine in FIG. 1. Conventionally, this combustion chamber that is of the annular type, comprises two coaxial annular walls, the radially inner wall 32 and the radially outer wall 34, that extend along the upstream to downstream direction 36 of the core engine gas flow in the turbomachine, about the centreline of the combustion chamber that is coincident with the axis 28 of the turbomachine. These inner annular 32 and outer annular 34 walls are connected to each other at their upstream end by an annular chamber dome wall 40 that extends approximately radially about the axis 28. This annular chamber dome wall 40 is fitted with injection systems 42 distributed around the axis 28 to enable injection of a premix of air and fuel centred on an injection axis 44.
During operation, part 46 of an airflow 48 from the compressor 16 supplies injection systems 42 while another part 50 of this airflow bypasses the combustion chamber flowing in the downstream direction along the coaxial walls 32 and 34 of this chamber and in particular supplies air orifices formed in these walls 32 and 34.
FIG. 3 is an axial half-sectional view of one of the injection systems 42. In general, this injection system comprises a bushing 54, sometimes called the <<sliding crossing>>, inside which a fuel injector head 52, an annular air inlet 56 and a bowl 58, sometimes called the “mixer bowl” are installed. These elements are centred on the injection axis 44 defined by the fuel injector head 52.
Throughout the following description, the <<upstream>> and <<downstream>> directions are defined within the injection system with reference to fuel injection along the injection axis 44.
The annular air inlet 56 comprises an annular separation wall 60 that divides the annular air inlet into an upstream air circulation space 62 and a downstream air circulation space 64. These two spaces are frequently called <<swirler sections>>.
The annular separation wall 60 is prolonged radially inwards as an annular deflection wall 66, frequently called <<venturi>>, with a convergent-divergent shaped internal profile 68, particularly with a neck 70 and an external profile 72.
The annular deflection wall 66 has a longitudinal axis coincident with the injection axis 44.
Each of the upstream 62 and downstream 64 air circulation spaces is crossed by fins 74 that spin the air about the injection axis 44.
During operation, some of the air 46 supplying the injection system penetrates into air circulation spaces 62 and 64 of the annular air inlet 56 and continues its path in the form of an airflow 76 and 78 respectively along the internal profile 68 and the external profile 72 of the deflection wall 66.
Furthermore, fuel is ejected by the injector head 52 in the form of a cone 80 with an angle θ relative to the injection axis 44.
A large proportion of this fuel is deposited and forms a film 82 on the internal profile 68 of the deflection wall 66.
The fuel is entrained by the airflow circulating in the downstream direction along this internal profile 68, and runs off towards the downstream direction on the internal profile 68.
When the fuel reaches the downstream end of the deflection wall 66, sometimes called the <<trailing edge>> by analogy with a wing, the fuel meets the airflow 78 passing along the external profile 72 of the deflection wall 66. This airflow 78 induces a shear effect that makes the fuel separate from the deflection wall, forming droplets in suspension in the air.
The fuel droplets separated from the annular deflection wall evaporate in air, preferably before reaching the inlet to the combustor in the combustion chamber.
The evaporation of droplets is facilitated as much as possible by turbulence induced by the confluence of the airflows 76 and 78 circulating on each side of the annular deflection wall.
However, this type of injection system is not optimum, because the extent of the downstream edge of the annular deflection wall that forms the fuel atomization zone is limited.
Consequently, the combustion efficiency is itself limited.

PRESENTATION OF THE INVENTION

The main purpose of the invention is to provide a simple, economic and efficient solution to this problem.
It discloses an annular deflection wall for a turbomachine combustion chamber injection system centred on a longitudinal axis, and having a free downstream edge.
Said downstream edge is formed by the repetition of a pattern extending on each side of a virtual circle.
Repetition of such a pattern increases the size of the fuel atomization zone formed by the downstream edge of the annular deflection wall.
The invention can also improve the air and fuel mix and therefore improve the combustion efficiency.
In particular, the invention can reduce the lean flameout richness and reduce CO/CH emissions.
More precisely, the annular deflection wall comprises a plurality of first bosses projecting radially outwards and a plurality of second bosses projecting radially inwards and arranged alternately with said first bosses, such that the downstream edge of the annular deflection wall that is formed from a set of downstream ends from said first and second bosses respectively, forms an undulation about said virtual circle.
The first and second bosses not only increase the size of the downstream edge and therefore the fuel atomization zone, but these bosses also increase the air/fuel exchange surface area on the internal surface of the annular deflection wall.
According to the invention, each of said first and second bosses is centred relative to a corresponding plane inclined from a corresponding median axial plane of the annular deflection wall passing through a corresponding extremum of the downstream edge of the annular deflection wall at the boss considered.
Preferably, the downstream edge of the annular deflection wall is inscribed in a plane orthogonal to the longitudinal axis of the annular deflection wall.
Preferably, said virtual circle is inscribed inside a virtual extension of a portion of revolution of the annular deflection wall.
The invention also relates to an annular air inlet for a turbomachine combustion chamber injection system comprising an annular separation wall that separates the annular air inlet into an upstream air circulation space and a downstream air circulation space that is extended radially inwards by an annular deflection wall of the type described above.
The invention also relates to an injection system for a turbomachine combustion chamber, comprising an annular air inlet of the type described above.
Preferably, the injection system also comprises a bushing to centre a fuel injector head arranged on the upstream side of the annular air inlet, and a bowl arranged on the downstream side of the annular air inlet.
The invention also relates to a combustion chamber for a turbomachine, comprising at least one injection system of the type described above.
Finally, the invention relates to a turbomachine, particularly of an aircraft, comprising at least one combustion chamber of the type described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other details, advantages and characteristics of it will become clear after reading the following description given as a non-limitative example with reference to the appended drawings in which:

FIG. 1, already described, is a diagrammatic axial partial sectional view of a known type of a turbomachine;

FIG. 2, already described, is a diagrammatic axial partial sectional view of a combustion chamber of the turbomachine in FIG. 1;

FIG. 3, already described, is a diagrammatic axial partial half-sectional view of an injection system installed in the combustion chamber in FIG. 2;

FIG. 4 is a perspective diagrammatic partial view of an annular deflection wall according to a preferred embodiment of the invention.

In all these figures, identical references may denote identical or similar elements.

DETAILED PRESENTATION OF PREFERRED EMBODIMENTS

FIG. 4 illustrates an annular deflection wall 100 according to a preferred embodiment of the invention, to substitute for the annular deflection wall 66 within the injection system 42 in FIG. 3.
The annular deflection wall 100 is different from the known type of the annular deflection wall 66, particularly in that the annular deflection wall 100 has a downstream edge 102 formed by the repetition of a pattern 104 extending on each side of a virtual circle 106, as will become clearer in the following.
The virtual circle 106 is preferably inscribed in a transvers plane R orthogonal to the longitudinal axis 44 of the annular deflection wall 100.
In the example shown, the annular deflection wall 100 generally comprises an upstream annular part 110 that is curved radially outwards towards the upstream end so as to have an internal profile 112 that converges in the downstream direction. This upstream annular part 110 connects to the separation wall 60 of the annular air inlet 56 of the injection system 42, in a manner similar to that shown in FIG. 3. The annular deflection wall 100 also comprises a downstream annular part 114 (FIG. 4) that has a free downstream edge that forms the above-mentioned downstream edge 102 of the annular deflection wall 100. This downstream annular part 114 comprises an upstream part forming a portion of revolution 118 about the longitudinal axis 44 of the annular deflection wall 100. The downstream annular part 114 has an internal surface 115 and an external surface 117.
In the illustrated embodiment, the portion of revolution 118 is cylindrical in shape. As a variant, this portion of revolution 118 may be tapered in shape.
In the example illustrated, the virtual circle 106 is defined along the extension of the portion of revolution 118. Consequently, when the portion of revolution 118 is cylindrical in shape, the virtual circle 106 is centred on the longitudinal axis 44 and its diameter is equal to the diameter of the portion of revolution 118, while when the portion of revolution 118 is tapered in shape, the virtual circle 106 that is also centred on the longitudinal axis 44, is inscribed in the cone centred on the longitudinal axis 44 and inside which the portion of revolution 118 is inscribed.
The annular deflection wall 100 comprises a plurality of bosses that are distributed into first bosses 120 projecting radially outwards and second bosses 122 projecting radially inwards. The first bosses 120 and the second bosses 122 are arranged alternately, downstream from the portion of revolution 118.
The downstream edge 102 of the annular deflection wall 100 is formed by a set of downstream ends 124, 126 of the first and second bosses 120, 122 respectively. Thus, due to the alternation of the first bosses 120 and the second bosses 122, the downstream edge 102 forms an undulation about the virtual circle 106.
Furthermore, each of the first and second bosses 120, 122 is centred relative to a plane P2 inclined by an angle α from a median axial plane P1 of the annular deflection wall 100 passing through one end 128 of the downstream edge 102 of the annular deflection wall at the boss 120, 122 considered.
In this case, the angle α is preferably chosen such that the general direction of the bosses is approximately coincident with the direction of the airflow put into rotation by the fins 74 of the annular air inlet 56 (FIG. 3).
In general, the downstream edge 102 of the annular deflection wall 100 is preferably inscribed in the transverse plane R orthogonal to the longitudinal axis 44 of the annular deflection wall 100, as is clear in FIG. 4.
In this case, the pattern 104 extends radially on each side of the virtual circle 106, in other words a part of the pattern 104 extends radially outside the virtual circle 106 while another part of the pattern 104 extends radially inside the virtual circle 106.
During operation, some of the air supplying the injection system penetrates into the upstream and downstream air circulation spaces of the annular air inlet, as in the injection system according to prior art shown in FIG. 3, and continues its path along the internal surface 115 and external surface 117 of the annular deflection wall 100 (FIG. 4).
Furthermore, a large proportion of the fuel ejected by the injector head is deposited and forms a film on the inside surface 115 of the annular deflection wall 100.
The fuel entrained by the airflow passing along this internal surface 115 in the downstream direction runs off towards the downstream direction on this surface.
When it reaches the downstream edge 102, the fuel meets the airflow circulating along the external surface 117 of the annular deflection wall 100. This airflow induces a shear effect that makes the fuel detach from the annular deflection wall, forming droplets in suspension in air.
Due to its shape, the downstream edge 102 has a larger fuel atomization zone than the downstream edge of a known type of annular deflection wall.
Bosses 120 and 122 can also increase the air/fuel exchange area on the internal surface 115 of the annular deflection wall 100.
In general, the repetition of a pattern extending on each side of a virtual circle as disclosed in the invention, can increase the fuel atomisation zone.
The invention can thus improve the air and fuel mix and therefore improve the combustion efficiency.
In particular, the invention can reduce the lean flameout richness and reduce CO/CH emissions.

Claims

1. An annular deflection wall for a turbomachine combustion chamber injection system centred on a longitudinal axis and having a free downstream edge, said annular deflection wall comprising a plurality of first bosses projecting radially outwards and a plurality of second bosses projecting radially inwards and arranged alternately with said first bosses, such that the downstream edge of the annular deflection wall, that is formed from a set of downstream ends from said first and second bosses respectively, forms an undulation about a virtual circle, said downstream edge being thus formed by the repetition of a pattern extending on each side of the virtual circle, wherein each of said first and second bosses is centred relative to a corresponding plane inclined by an angle α from a corresponding median axial plane of the annular deflection wall passing through a corresponding extremum of the downstream edge of the annular deflection wall at the boss considered.

2. The annular deflection wall according to claim 1, wherein said virtual circle is inscribed inside a virtual extension of a portion of revolution of the annular deflection wall.

3. The annular deflection wall according to claim 1, in which the downstream edge of the annular deflection wall is inscribed in a transverse plane orthogonal to the longitudinal axis of the annular deflection wall.

4. An annular air inlet for an injection system of a combustion chamber of a turbomachine, comprising an annular separation wall that divides the annular air inlet into an upstream air circulation space and a downstream air circulation space and that is prolonged radially inwards by an annular deflection wall according to claim 1.

5. A turbomachine, particularly for an aircraft, comprising at least one combustion chamber comprising at least one injection system comprising an annular air inlet according to claim 4.