U.S. patent application number 11/181924 was filed with the patent office on 2006-12-28 for after-burner chamber with secure ignition.
This patent application is currently assigned to SNECMA MOTEURS. Invention is credited to Sebastien Pierre Louis Baboeuf, Sabine Constance Maud Charpenel, Didier Noel Durand, Jacques Andre Michel Roche.
Application Number | 20060292504 11/181924 |
Document ID | / |
Family ID | 34947700 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060292504 |
Kind Code |
A1 |
Baboeuf; Sebastien Pierre Louis ;
et al. |
December 28, 2006 |
After-burner chamber with secure ignition
Abstract
A turbojet having an after-burner chamber presenting a specific
injector opening into the burner ring to provide secure ignition.
The after-burner chamber has an annular fuel injection duct, an
ignition spark plug, and an ignition injector installed facing the
spark plug and connected to specific fuel feed means.
Inventors: |
Baboeuf; Sebastien Pierre
Louis; (Avon, FR) ; Charpenel; Sabine Constance
Maud; (Brunoy, FR) ; Durand; Didier Noel;
(Pontault-Combault, FR) ; Roche; Jacques Andre
Michel; (Lisses, FR) |
Correspondence
Address: |
C. IRVIN MCCLELLAND;OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SNECMA MOTEURS
Paris
FR
|
Family ID: |
34947700 |
Appl. No.: |
11/181924 |
Filed: |
July 15, 2005 |
Current U.S.
Class: |
431/5 |
Current CPC
Class: |
F23R 3/20 20130101 |
Class at
Publication: |
431/005 |
International
Class: |
F23G 7/08 20060101
F23G007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2004 |
FR |
0407909 |
Claims
1. An after-burner chamber comprising an annular fuel injection
duct and an ignition spark plug mounted in the vicinity of said
annular duct, wherein an ignition injector is installed facing said
spark plug and is connected to specific fuel feed means suitable
for delivering said fuel under a controlled pressure independent of
the feed conditions to said annular duct.
2. An after-burner chamber according to claim 1, wherein said
injector is fitted with a nozzle for spraying said fuel finely.
3. An after-burner chamber according to claim 1, in which said
annular duct is mounted in a burner ring, wherein said injector is
mounted in said burner ring and opens out to the inside thereof, in
the vicinity of said spark plug.
4. An after-burner chamber according to claim 2, of the type in
which said burner ring is placed in the hot primary stream of said
after-burner chamber, wherein the injector and the spark plug are
housed in a protective sheath fastened to an outer casing and
opening out into said burner ring.
5. An after-burner chamber according to claim 4, wherein said
protective sheath has ventilation orifices communicating with the
cold secondary stream of said after-burner chamber.
6. A turbojet including an after-burner chamber according to claim
1.
Description
[0001] The invention relates to an after-burner chamber for a
turbojet, and more particularly it relates to an improvement in the
ignition system for said after-burner.
BACKGROUND OF THE INVENTION
[0002] After-burning is used in military aircraft to increase the
thrust of the engine quickly, and consequently to increase the
speed of the airplane, when flying conditions make that
necessary.
[0003] U.S. Pat. No. 5,396,761 describes an after-burner chamber
having a plurality of burners extending radially, one of which is
fitted with an ignition system comprising a spark plug associated
with an injector. The injector has orifices facing away from the
spark plug, such that ignition is not ensured under all operating
conditions of the jet.
[0004] U.S. Pat. No. 3,931,707 describes an after-burner chamber
fitted with a burner ring having a plurality of nozzles delivering
fuel upstream from a ring of stationary vanes where the fuel mixes
with air entering the ring via a downstream slot. A spark plug
serves to ignite the fuel. However, there is nothing to control
vaporization of the fuel to ensure that the mixture will ignite
under all flying conditions.
OBJECTS AND SUMMARY OF THE INVENTION
[0005] The invention applies to a similar type of combustion
chamber fitted with an annular burner and a spark plug capable of
generating sparks for igniting after-burning. In such a system, the
end of the spark plug is placed facing a point on an annular fuel
distribution duct. In that type of after-burner, depending on the
altitude and the speed of the airplane when after-burning is
triggered, the pressure and the temperature at which fuel is
injected into the duct can be too low or too variable. It is not
possible to act directly on the injection pressure in the annular
duct. Consequently, ignition is not certain and sometimes
after-burning is not triggered, and that is not necessarily due to
the spark plugs operating poorly. The invention serves to solve
this problem.
[0006] More particularly, the invention provides an after-burner
chamber comprising an annular fuel injection duct and an ignition
spark plug mounted in the vicinity of said annular duct, wherein an
ignition injector is installed facing said spark plug and is
connected to specific fuel feed means suitable for delivering said
fuel under a controlled pressure independent of the feed conditions
to said annular duct.
[0007] Thus, the specific ignition injector fed by a fuel source
that is different from that which feeds the burner and that is used
for spraying fuel for a few seconds in front of the ignition spark
plug, guarantees that after-burning will ignite.
[0008] Once after-burning has started, the specific feed source for
the ignition injector can be switched off until the next time
after-burning is to be triggered. The spark plug issues several
sparks per second until ignition occurs. The ignition period lasts
for a few seconds, e.g. three seconds to ten seconds.
[0009] The injector is provided with a special nozzle that
vaporizes the jet into particles that are very fine, being smaller
than fifty micrometers.
[0010] In an embodiment in which the annular duct is mounted in a
burner ring, said injector projects inwards from said ring, behind
the spark plug.
[0011] In an after-burner chamber, it is conventional to
distinguish between a hot inner primary stream in which the gas
delivered by the turbine flows, and a cooler outer secondary stream
that is separated from the primary stream by a shroud. When the
burner ring is placed in the hot primary stream, -the injector and
the spark plug are housed in a protective sheath fastened to an
outer casing, commonly referred to as the heater casing and opening
out into said burner ring. The protective sheath isolates the
ignition system from said hot primary stream. In addition, the
protective sheath advantageously includes ventilation orifices
communicating with the cold secondary stream. In this way, cold air
flows continuously inside the protective sheath in order to keep
the ignition system at an acceptable temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be better understood and other advantages
thereof will appear better in the light of the following
description of a turbojet having an after-burner chamber in
accordance with the principles of the invention, and given purely
by way of example, with reference to the accompanying drawings, in
which:
[0013] FIG. 1 is a fragmentary half-section of the upstream portion
of an after-burner chamber in which the burner ring is placed in
the secondary stream;
[0014] FIG. 2 is a diagram on a larger scale showing the
disposition of the aeromechanical injector and of the ignitor spark
plug relative to the burner ring;
[0015] FIG. 3 is a perspective view of the burner ring seen looking
along arrow 3 in FIG. 2 and showing the connection of the specific
injector;
[0016] FIG. 4 is a perspective view looking along arrow 4 in FIG. 2
and showing the burner ring and the specific injector; and
[0017] FIG. 5 is a section view on a radial plane through the
after-burner chamber showing the ignition system of the burner ring
when the ring is situated in the relatively hot primary stream.
MORE DETAILED DESCRIPTION
[0018] With reference to FIGS. 1 to 4, there can be seen a portion
of the after-burner chamber 11 of a turbojet 12, situated
downstream from the turbine (not shown) on its axis X'X.
Conventionally, the casing 14 of the after-burner chamber is
connected by bolts to the end of a diffuser casing 16 also referred
to as a heater casing. An inner exhaust casing 18 is connected to
an exhaust cone 19 extending axially in the central portion of said
diffuser casing 16.
[0019] In the space defined between said diffuser casing 16 and the
casing 18 together with the cone 19, there is a "confluence" shroud
20 which separates and channels the inner primary gas stream
F.sub.1 and the outer secondary gas stream F.sub.2. The primary
stream F.sub.1 of gas from the turbine is at high temperature while
the secondary stream F.sub.2 coming from the compressor is at
relatively low temperature and enables the structural elements of
the after-burner chamber to be cooled. An inner jacket 22 carried
by the casing 14 defines the after-burner chamber downstream from a
combustion system 25 essentially comprising a burner ring 26 and
radial arms 27 extending from the burner ring towards the inside of
the after-burner chamber almost as far as the axis X'X thereof.
[0020] Between them, the jacket 22 and the casing 14 define an
annular cooling channel 28 extending around the after-burner
chamber 11.
[0021] There are nine radial arms 27 that are regularly distributed
circumferentially. Each arm is of V-shape section, with its limbs
diverging rearwards and forming two rectilinear ducts for ejecting
sprayed fuel, constituting a "flame-holder" structure. In its
radially-outermost portion, each arm presents an aerodynamically
profiled element 30 whereby it is connected to the casing 16. This
element enables the secondary stream to be channeled, in particular
towards the annular cooling channel 28. These arms for maintaining
combustion at the center of the after-burner chamber are of
conventional design and are not concerned by the invention; they
are therefore not described in greater detail herein.
[0022] The burner ring 26 of the after-burner system 25 is
substantially circularly symmetrical about the axis X'X; it is
carried by the elements 30. The burner ring opens rearwards between
the arms 27 and the internal jacket 22. The portion that is open
rearwards presents a section that is V-shaped on a radial plane
containing the axis X'X. The burner ring 26 houses an annular fuel
injection duct 34 comprising an internal spray tube 36 pierced by a
plurality of very small diameter holes 35 and extending inside a
protective tube 38 (pierced by holes of relatively large diameter
that are regularly spaced apart circumferentially) forming a screen
against radiation in order to provide the spray tube with thermal
protection. Advantageously, the holes 35 of the spray tube 36
coincide with the holes in the protective tube 38. The annular duct
34 extends over practically the entire circumference of the burner
ring 26. In known manner, said burner ring is fed with fuel via a
duct 40 connected to a main source of fuel (not shown).
[0023] At a point around the burner ring 26, an ignitor spark plug
42 is conventionally installed in the vicinity of the annular spray
duct 34. It is slidably engaged in a sleeve 43 which has a flange
44, itself sliding in the space defined between the outer wall of
the burner ring 26 and a frame 45 welded thereto about the hole
through which the end of the spark plug penetrates into said burner
ring.
[0024] According to an important characteristic of the invention,
an ignition injector 48 is installed facing said spark plug 42 and
is connected to specific fuel feed means that are adapted to
deliver said fuel under a pressure that is controlled and
independent of the feed conditions to said annular duct. The
injector 48 is itself said to be "specific" since it is fed by a
special fuel source (not shown) via its own duct 49.
[0025] The spray endpiece of the injector 48 which projects into
the burner ring is slidably engaged in a sleeve 47 which includes a
flange 50, itself sliding in the space defined between the wall of
the burner ring (at the front thereof) and a frame 51 welded
thereto about the hole through which said endpiece penetrates into
the burner ring.
[0026] In this example, the specific injector 48 is of the
aeromechanical type. It is provided with a nozzle for delivering a
fine spray of fuel, capable of delivering particles of a size
smaller than fifty micrometers. The injector is placed in such a
manner that the end of the spark plug 42 (where the spark occurs)
lies in the vaporization cone 54 of the injector.
[0027] FIG. 5 shows a variant in which the burner ring 26a is
disposed in the hot primary stream F.sub.1 (which depends on the
general design of the jet). In this embodiment, structural elements
that are analogous to those described above are given the same
numerical references. They are not described again. Because of the
location of the burner ring, provision is made to protect the
ignitor system (specific injector 48a and spark plug 42a) in a
protective sheath 60 fastened to the casing 16 and communicating
with the burner ring. Said sheath 60 thus passes through the
secondary stream F.sub.2.
[0028] In addition, the protective sheath has ventilation orifices
62 communicating with the cold secondary stream. Thus, the inside
of the sheath continuously carries a flow of cold air. A thermal
protection screen 64 is also placed between the injector and the
end of the spark plug. It presents a passage 65 facing the spray
orifice of the specific injector. An annular ventilation box 66 is
installed inside the burner ring 26a.
[0029] When after-burning is ignited, fuel is injected into the
burner ring 26 and the arms 27, and simultaneously, although under
different pressure conditions, a small quantity of additional fuel
is injected by means of the specific injector 48. The sparks
produced by the spark plug 42 occur in the spray-cone of the
injector, thereby causing the fuel injected by the specific
injector to ignite, followed by the fuel delivered along the burner
ring and the arms.
* * * * *