3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which
it is to be performed:
2
DESCRIPTION
TECHNICAL FIELD
The present invention relates to the field of turbomachine combustion
chambers, especially intended to equip aircrafts.
The invention more particularly relates to the cooling of an annular wall
of such a combustion chamber equipped with a port for an ignition plug.
STATE OF PRIOR ART
Figure 1 illustrates a typical example of a known type turbomachine 1,
for example, an aircraft twin spool turbofan engine.
The turbomachine 1 successively comprises, along the thrust direction
represented by the arrow 2 also corresponding to the general direction of gas flow in the
turbofan, a low pressure compressor 4, a high pressure compressor 6, an annular
combustion chamber 8, a high pressure turbine 10 and a low pressure turbine 11.
In a well-known manner, the combustion chamber 8 is mounted
downstream from the high pressure compressor 6 provided for supplying this chamber
with pressurized air, and upstream from the high pressure turbine 10 provided for
rotating the high pressure compressor 6 under the effect of gas thrust coming from the
combustion chamber.
Figure 2 illustrates on larger scale the combustion chamber 8 and its
close environment.
The combustion chamber 8 comprises two respectively radially inner 12
and radially outer 13 coaxial annular walls, which extend around the longitudinal axis 14
of the combustion chamber.
These two annular walls 12 and 13 are fixed downstream to inner 15
and outer 16 casings of the chamber, and are connected to each other at their upstream
end by a chamber annular end wall 18.
3
The chamber annular end wall 18 includes an annular row of ports
evenly distributed around the axis 14 of the combustion chamber, and in which injection
systems 20 are mounted, associated with an annular row of fuel injectors 22 each having
a fuel emission axis 24.
Each injection system 20 includes ports for injecting, in the combustion
chamber, part of the airflow 26 coming from the diffuser 28 mounted at the outlet of the
high pressure compressor of the turbomachine.
Besides, the annular walls 12 and 13 of the combustion chamber are
connected at their upstream end to an annular shroud 30 including ports aligned with the
injection systems 20 for passing injectors 22 and air supplying the injection systems 20.
The main functions of this shroud 30 are to protect the chamber end wall 18 and to guide
parts 32 and 34 of the airflow 26 which respectively travel downstream along the inner 12
and outer 13 annular walls of the combustion chamber, within two respectively inner 36
and outer 38 bypass spaces. Hereinafter, the parts 32 and 34 of the airflow 26 are
respectively referred to as “inner bypass airflow” and “outer bypass airflow”. The inner 36
and outer 38 bypass spaces form, with an upstream space 39 which connects one to the
other, an annular enclosure in which the combustion chamber 8 extends.
The annular walls 12 and 13 of the combustion chamber each include
two annular rows of air inlet ports 40, 42 for injecting part of each bypass airflow 32, 34 in
the combustion chamber.
A first one of these rows of ports is formed around an upstream
region 44 of the combustion chamber commonly referred to as a “primary area”, in which
the combustion reactions of the air and fuel mixture occur in operation. For this reason,
the ports 40 of this first row are commonly referred to as “primary ports”.
The second row of ports is formed downstream around a region 46 of
the chamber commonly referred to as a “dilution area” in which the combustion gases
are diluted and cooled. For this reason, the ports 42 of this second row are commonly
referred to as “dilution ports”.
The annular walls 12 and 13 are further provided with numerous microperforations
substantially distributed on the whole surface of these walls and intended to
4
create a cooling air film along each of these walls within the combustion chamber 8.
These micro-perforations, which generally have diameters between 0.3 and 0.6mm
approximately, are not represented in Figure 2 for reasons of scale.
Besides, the radially outer annular wall 13 includes a plug port 46,
having an axis 47, and fitted with a guiding bushing 48 in which an ignition plug 50
extends, mounted on the outer casing 16 and intended to initiate the combustion of the
air and fuel mixture at the start of the turbomachine.
It is to be noted that hereinafter, the term “combustion chamber
module” refers to an assembly comprising at least the combustion chamber 8 and the
ignition plug 50.
However, the ignition plug 50 and the bushing 48 produce a wake 52
within the outer bypass airflow 34, as illustrated in Figure 3.
This wake 52 develops downstream by being centred relative to a
median axial plane P of the plug port 46, in the case where the airflow 26 (Figure 2)
supplied by the high pressure compressor flows downstream substantially without a
gyratory component. This can be the case when the high pressure compressor is of the
axial type, as in the illustrated example.
On the other hand, in the case where the airflow 26 supplied by the high
pressure compressor flows downstream helically, that is with a gyratory component, the
wake 52 generally develops downstream along a tilted direction relative to the median
axial plane P of the plug port 46. This can be the case especially when the high pressure
compressor is of the centrifugal type.
It is to be noted that “axial plane” means a plane passing through the
axis 14 (Figure 2) of the combustion chamber 8, which merges with the axis of the
turbomachine. It is to be noted that the plane P corresponds to the section plane of
Figure 2.
It is also to be noted that Figure 3 illustrates the micro-perforations 53
which ensure the cooling of the radially outer annular wall 13. For the sake of clarity,
these micro-perforations are represented larger and distributed according to a lesser
density than in reality.
5
In every case, the wake 52 results in a depression in the region of the
outer bypass airflow 34 concealed by the plug guiding bushing 48.
Figure 4 represents the total pressure Ptot of this airflow 34 as a
function of the position d measured along the transverse segment S of Figure 3.
Hereinafter, for each segment S, a wake area 54 (Figure 3) is defined as being an area of
the segment S in which the total pressure Ptot of the airflow 34 is lower than 99 % of the
maximum Ptotmax taken by this total pressure along this segment S. A wake 52 is defined
as being a gathering of adjoining wake areas 54 succeeding from upstream to
downstream from the plug port 46.
But, the presence of such a wake disrupts the efficiency of the cooling
ensured by the micro-perforations 53.
Indeed, the flow of air through micro-perforations 53 of the
radially outer wall 13 results from the difference between the total pressure Ptot of the
bypass airflow 34 and the static pressure within the combustion chamber 8. This pressure
difference is generally in the order of 3 %. Due to this, the total pressure drop in the order
of 1 % noticed within the wake 52 induces a loss of flow within micro-perforations that
can reach about 20 % or even more.
Such a decrease in the efficiency of the cooling of the abovementioned
annular wall results in a diminution of the lifetime of this wall, and also in a risk of
loosening of the plug guiding bushing.
DISCLOSURE OF THE INVENTION
The purpose of the invention is especially to bring a simple, economical,
and efficient solution to this problem.
To do so, it provides a combustion chamber module for a turbomachine,
comprising:
an annular enclosure,
an annular combustion chamber accommodated in said annular enclosure and
including at least one annular wall delimiting said combustion chamber and including a
6
plug port as well as a plurality of micro-perforations to let in cooling air in said
combustion chamber for cooling said annular wall, and
an ignition plug extending in said annular enclosure and through said plug port.
This combustion chamber module is intended to receive an airflow
coming from a turbomachine compressor and generally flowing from upstream to
downstream of the combustion chamber within said annular enclosure, and a part of
which is designed to bypass the combustion chamber by running along said annular wall
thereof and by immersing said ignition plug which thus creates a wake.
According to the invention, said combustion chamber module further
comprises deflection means extending from upstream to downstream by approaching a
median plane of said wake and by approaching said annular wall of the combustion
chamber, so as to divert, towards said median plane of said wake and towards said
annular wall of the combustion chamber, part of the air immersing said ignition plug.
The thus diverted air enables the total pressure of air to be increased
within the wake induced by the ignition plug, in proximity to the annular wall of the
combustion chamber, and therefore the pressure difference to be increased between said
wake and the inside of the combustion chamber.
As a result, the convective transfer through the micro-perforations of
said annular wall is improved, and therefore risks of cracks occurring and risks of metal
loss are reduced, and consequently generally speaking, the lifetime of this annular wall is
improved.
When the ignition plug is guided through the sidewall of the combustion
chamber by means of a bushing mounted in the plug port, the invention also enables the
risks of bushing disengagement to be reduced.
“Bushing” means any type of device, possibly in several parts, enabling
the plug to be guided through the annular wall of the combustion chamber, as will appear
more clearly hereinafter.
In a first preferred embodiment of the invention, said deflection means
comprise two ducts each delimited by a first tangential wall arranged facing the annular
wall of the combustion chamber, a second tangential wall arranged on the opposite side
7
with respect to the annular wall of the combustion chamber, a first sidewall arranged on
the side of the ignition plug, and a second sidewall arranged on the opposite side with
respect to the ignition plug.
Moreover, each of said ducts advantageously has at least one air inlet to
draw air to be diverted as well as at least one air outlet to diffuse the diverted air towards
said median plane of said wake.
Furthermore, said respective second sidewalls of said ducts
advantageously form deflecting walls provided on either side of said ignition plug and
extending from upstream to downstream by approaching said median plane of said wake.
Finally, said respective tangential walls of said ducts advantageously
extend in the downstream direction by approaching the annular wall of the combustion
chamber.
Said ducts are advantageously carried by an annular support extending
around said ignition plug.
Alternatively, said deflection means can comprise a curved duct
extending around a portion of said plug port and having two air inlets formed at two
opposite ends of said duct to draw air to be diverted, and at least one air outlet port
formed in a median part of a wall delimiting said duct and opening into said wake.
In this case, said duct is preferably fitted in a bushing mounted in said
plug port and intended to guide said ignition plug.
In a second preferred embodiment of the invention, said deflection
means comprise a deflecting wall connected to a casing surrounding said combustion
chamber and delimiting said annular enclosure, said deflecting wall being shaped so that,
when seen in cross-section along any plane parallel to said median plane of said wake,
said deflection wall extends in the downstream direction by approaching said annular wall
of the combustion chamber, and when seen in cross-section along any plane orthogonal
to an axis of said ignition plug, said deflecting wall extends in the downstream direction
by approaching said median plane of said wake.
Said deflecting wall is preferably inscribed in a virtual rotational cylinder
having a tilted axis relative to a plane orthogonal to the axis of said ignition plug.
8
The invention also relates to a turbomachine, comprising a combustion
chamber module of the above-described type, as well as a compressor opening into said
annular enclosure of said combustion chamber module.
It is to be noted that when said compressor is designed to deliver an
airflow without a gyratory component to said combustion chamber module, said median
plane of said wake is then a median axial plane of said plug port.
The invention also relates to a method for designing a combustion
chamber module of the above-described type for an aircraft turbomachine comprising a
compressor intended to deliver an airflow to said combustion chamber module.
According to the invention, the method comprises determining the
wake produced by said ignition plug in said part of the airflow immersing said ignition
plug, and then geometrically defining said deflection means so that the latter extend from
upstream to downstream by approaching said median plane of said wake and by
approaching said annular wall of the combustion chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood, and further detail, features and
characteristics thereof will appear upon reading the following description made by way of
non-limiting example and with reference to the accompanying drawings in which:
Figure 1, already described, is an axial cross-section partial schematic view of a
known type turbomachine;
Figure 2, already described, is an axial cross-section partial schematic half-view of
an annular combustion chamber of the turbomachine of Figure 1;
Figure 3, already described, is a top partial schematic view of a radially outer
annular wall of the combustion chamber of Figure 2;
Figure 4, already described, is a graph representing the total pressure (on the
abscissa) as a function of the circumferential position (on the ordinate) along the
transverse segment S of Figure 3 ;
Figures 5 and 6 are partial schematic perspective views of a combustion chamber
module according to a first preferred embodiment of the invention;
9
Figure 7 is an axial cross-section partial schematic view of a combustion chamber
module according to a second preferred embodiment of the invention;
Figure 8 is a partial schematic view of the combustion chamber module of Figure 7,
in cross-section along a plane P1;
Figure 9 is a schematic perspective view of a deflecting wall of the combustion
chamber module of Figure 7.
Throughout these figures, identical references can refer to identical or
analogous elements.
DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS
Figures 5 and 6 illustrate a combustion chamber module of a
turbomachine according to a first embodiment of the invention, and more particularly
represent a region of the radially outer annular wall 13 of the combustion chamber,
provided with a plug port 46 in which a bushing 48 is mounted.
The combustion chamber module also includes an ignition plug
mounted in the bushing 48, but this ignition plug is not represented in Figures 5 and 6 for
the sake of clarity. The combustion chamber module also includes an annular enclosure
delimited by inner and outer casings and in which the combustion chamber is
accommodated, similarly to the example of Figure 2. These elements can also not be seen
in Figures 5 and 6. These Figures 5 and 6 also show primary ports 40 and dilution ports 42,
as well as micro-perforations 53, these elements being for example of a conventional
type.
In the illustrated example, the turbomachine under consideration
includes a compressor designed to deliver an airflow without a gyratory component to
the combustion chamber module. Such an airflow thus generally flows along a direction
parallel to the axis 14 of the combustion chamber.
In this case, as explained above, the wake 52 induced by the ignition
plug and by the associated bushing is substantially centred relative to the median axial
plane P of the plug port 46. This latter plane thus forms a median plane of the wake.
10
According to the invention, the combustion chamber module further
includes deflection means to divert part of the air 34’ traveling in proximity to the ignition
plug towards the median plane P of the wake and of the radially outer annular wall 13 of
the combustion chamber, as will appear more clearly hereinafter.
Thus, in the first embodiment illustrated in Figures 5 and 6, the
deflection means include two ducts 60 each delimited by a first tangential wall 62
arranged facing the annular wall 13 of the combustion chamber, a second tangential
wall 64 arranged on the opposite side with respect to the annular wall 13 of the
combustion chamber, a first sidewall 66 arranged facing the bushing 48, and a second
sidewall 68 arranged on the opposite side with respect to the bushing 48. Both sidewalls
66, 68 are each connected to both tangential walls 62, 64, and the latter are connected to
an annular support 70 engaged on the bushing 48 so as to extend around the ignition
plug.
The tangential walls 62 and 64 of each duct are shaped so as to extend
towards downstream by approaching the annular wall 13 of the combustion chamber, so
as to increase the action of the diverted air in the region of the wake 52 located in
proximity to the bushing 48.
Each of the ducts 60 has an air inlet 72 facing upstream, as well as a first
air outlet 74 facing downstream and towards the median plane P of the wake. In the
illustrated example, each duct is continued beyond the first air outlet 74 by a duct
extension 75 having a second air outlet 76.
The second sidewall 68 of each of the ducts 60 extends towards
downstream by approaching the median plane P of the wake, and thus forms a deflecting
wall able to divert the air entering the duct towards said plane.
In the illustrated example, the second sidewall 68 of each of the
ducts 60 extends parallel to the axis of the ignition plug, which coincides with the axis 47
of the plug port 46. The second sidewall 68 is thus substantially orthogonal to the annular
wall 13 of the combustion chamber.
Each duct extension 75 is delimited by an extension of each of the
tangential walls 62 and 64, and by a first extension sidewall 78 provided on the side of the
11
median plane P of the wake and a second extension sidewall 80 provided on the opposite
side. The latter wall extends towards downstream by approaching the median plane P of
the wake, with a higher approaching rate than the one of the corresponding second
sidewall 68. This second extension sidewall 80 thus also forms a deflecting wall, according
to the terminology of the invention.
Moreover, in the illustrated example, both ducts 60 are symmetrically
arranged relative to the median plane P of the wake.
In operation, part of the air supplied to the combustion chamber
module by the compressor of the turbomachine travels in the outer bypass space 38
along the radially outer annular wall 13 of the combustion chamber. A portion 34’ of this
air, passing in proximity to the ignition plug and the associated bushing 48, enters the
ducts 60 and is guided by the second sidewalls 68 and by the second extension
sidewalls 80. The ducts 60 thus deliver through their outlets 74 and 76 an airflow 82
diverted towards the median plane P of the wake and the outer annular wall 13 of the
combustion chamber. As a result, the total pressure of air is increased in the
corresponding area of the wake 52 in proximity to the annular wall 13, enabling the
convective exchanges to be improved through the micro-perforations 53, and thus the
cooling of the annular wall 13 to be improved.
In a second preferred embodiment of the invention illustrated in
Figures 7 to 9, the deflection means include a deflecting wall 90 connected to the outer
casing 16 (Figures 7 and 2) surrounding the combustion chamber 8 and delimiting the
annular enclosure in which this combustion chamber is accommodated.
This deflecting wall 90 is shaped so that, when seen in cross-section
along any plane parallel to the median plane P of the wake, the deflecting wall 90 extends
towards downstream by approaching the annular wall 13 of the combustion chamber,
and so that, when seen in cross-section along any plane orthogonal to the axis of the
ignition plug which coincides with the axis 47 of the plug port 46, the deflecting wall 90
extends towards downstream by approaching the median plane P of the wake.
12
For this purpose, in the illustrated example, the deflecting wall 90 is
inscribed in a virtual cylinder of revolution 92, as illustrated in Figure 9. More precisely,
the deflecting wall 90 corresponds to a section of the cylinder 92 delimited by two
planes P1 and P2 which intersect along a line D orthogonal to the axis 94 of the cylinder
92. The plane P1 delimits an upper rim of the deflecting wall 90, through which the latter
is connected to the outer casing 16. The plane P1 is thus tangent to this casing 16, and is
for example orthogonal to the axis 47 of the plug port 46. The plane P2 delimits a lower
rim of the deflecting wall 90. Both planes P1 and P2 have an angle θ therebetween, for
example equal to about 30 degrees. Moreover, the axis 94 of the virtual cylinder 92 is for
example at an angle α equal to about 45 degrees with the axis 47 of the plug port 46. The
axis 94 of the cylinder is thus tilted relative to the plane P1.
By way of example, as shown in Figure 7, the outer casing 16 includes a
boss 95 provided with a port through which the ignition plug 50 extends. The deflecting
wall 90 is then advantageously fixed on this boss 95.
Figure 7 also shows a more detailed example bushing 48 intended to
guide the ignition plug 50. This bushing 48 includes a plug guide 96 mounted on a
chimney 98 and retained on the latter by an annular piece 100 sometimes referred to as a
“cup”, as well as a ring 102 crimped in the plug port 46 and in which the chimney 98 is
crimped. In a manner known per se, the plug guide 96 thus has a freedom of movement
perpendicularly to the axis 47 of the plug port 46, which enables the bushing 48 to
support the deformations of the combustion chamber module induced by the usual
phenomena of differential expansions.
In operation, as illustrated in Figures 7 and 8, part of the air supplied to
the combustion chamber module by the compressor of the turbomachine travels in the
outer bypass space 38 along the radially outer annular wall 13 of the combustion
chamber. A portion 34’ of this air, passing in proximity to the ignition plug, travels
towards the deflecting wall 90 and is diverted by the latter so as to constitute an
airflow 104 diverted towards the median plane P of the wake and towards the annular
wall 13 of the combustion chamber.
13
As a result, the total pressure of air is again increased in the area
corresponding to the wake, enabling the convective exchanges to be improved through
micro-perforations of the annular wall 13.
In the illustrated example, the deflecting wall 90 further makes it
possible to conceal a region of the outer casing 16 located downstream of the boss 95 of
the latter, and thus makes it possible to reduce the level of heat transfer by convection
between air and the outer casing 16 at this area. As a result, the heat constraints applied
to this particularly exposed area of the outer casing 16 are reduced, and therefore the
lifetime of this casing is improved.
Generally speaking, the invention thus makes it possible to improve the
lifetime of the annular wall 13 of the combustion chamber in the region of the wake 52
and to reduce the risks of loosening of elements forming the bushing 48 intended to
guide the ignition plug through the annular wall 13.
The invention can further make it possible to improve the lifetime of the
outer casing 16 when the latter has a boss 95 such as above-described.
In the examples above-described with reference to the accompanying
figures, the compressor of the turbomachine is of the type delivering an airflow 34’
without a gyratory component, so that the median plane P of the wake is a plane passing
through the axis 14 of the combustion chamber.
Of course, the invention also applies to turbomachines the compressor
of which is designed to deliver an airflow according to a gyratory movement. In this case,
the median plane P of the wake is tilted relative to the axis 14 of the combustion
chamber, and the orientation of the deflecting means according to the invention can be
adapted accordingly.
14
We claim:
1. A combustion chamber module for a turbomachine, comprising:
an annular enclosure (36, 38, 39),
an annular combustion chamber (8) accommodated in said annular enclosure and
including at least one annular wall (13) delimiting said combustion chamber and including
a plug port (46) as well as a plurality of micro-perforations (53) to let in cooling air in said
combustion chamber for cooling said annular wall (13), and
an ignition plug (50) extending in said annular enclosure and through said plug
port (46),
said module being intended to receive an airflow (26) coming from a turbomachine
compressor and generally flowing from upstream to downstream of the combustion
chamber within said annular enclosure, and a part (34’) of which is designed to bypass the
combustion chamber by running along said annular wall (13) thereof and by immersing
said ignition plug (50) which thus creates a wake (52),
said combustion chamber module being characterized in that it further comprises
deflection means (60, 64, 68, 90) extending from upstream to downstream by
approaching a median plane (P) of said wake and by approaching said annular wall (13) of
the combustion chamber, so as to divert, towards said median plane (P) of said wake and
towards said annular wall (13), part (82, 104) of the air immersing said ignition plug.
2. The combustion chamber module according to claim 1, wherein:
said deflection means comprise two ducts (60) each delimited by a first tangential
wall (62) arranged facing the annular wall (13) of the combustion chamber, a second
tangential wall (64) arranged on the opposite side with respect to the annular wall (13) of
the combustion chamber, a first sidewall (66) arranged on the side of the ignition
plug (50), and a second sidewall (68) arranged on the opposite side with respect to the
ignition plug (50);
15
each of said ducts has at least one air inlet (72) to draw air to be diverted as well as
at least one air outlet (74, 76) to diffuse the diverted air (82) towards said median
plane (P) of said wake;
said respective second sidewalls of said ducts form deflecting walls (68) provided on
either side of said ignition plug (50) and extending from upstream to downstream by
approaching said median plane (P) of said wake;
said respective tangential walls (62, 64) of said ducts extend in the downstream
direction by approaching the annular wall (13) of the combustion chamber.
3. The combustion chamber module according to claim 2, wherein
said ducts (60) are carried by an annular support (70) extending around said ignition
plug (50).
4. The combustion chamber module according to claim 1, wherein
said deflection means comprise a curved duct extending around a portion of said plug
port and having two air inlets formed at two opposite ends of said duct to draw air to be
diverted, and at least one air outlet port formed in a median part of a wall delimiting said
duct and opening into said wake.
5. The combustion chamber module according to claim 4, wherein
said duct is fitted in a bushing mounted in said plug port and intended to guide said
ignition plug.
6. The combustion chamber module according to claim 1, further
comprising a casing (16) surrounding said combustion chamber and delimiting said
annular enclosure (36, 38, 39), said deflection means comprising a deflecting wall (90)
connected to said casing (16), said deflecting wall (90) being shaped so that, when seen in
cross-section along any plane parallel to said median plane (P) of said wake, said
deflecting wall extends in the downstream direction by approaching said annular wall (13)
of the combustion chamber, and when seen in cross-section along any plane (P1)
16
orthogonal to an axis (47) of said ignition plug, said deflecting wall extends in the
downstream direction by approaching said median plane (P) of said wake.
7. The combustion chamber module according to claim 6, wherein
said deflecting wall (90) is inscribed in a virtual cylinder of revolution (92) having an
axis (94) inclined relative to a plane (P1) orthogonal to the axis (47) of said ignition plug.
8. A turbomachine, comprising a combustion chamber module
according to any of the preceding claims, as well as a compressor opening into said
annular enclosure of said combustion chamber module.
9. A method for designing a combustion chamber module according
to any of claims 1 to 7 for an aircraft turbomachine comprising a compressor intended to
deliver an airflow (26) to said combustion chamber module, characterized in that it
comprises determining the wake (52) produced by said ignition plug (50) in said part (34’)
of the airflow immersing said ignition plug, and then geometrically defining said
deflection means (60, 68, 90) so that the latter extend from upstream to downstream by
approaching said median plane (P) of said wake and by approaching said annular wall (13)
of the combustion chamber.