U.S. patent application number 12/453776 was filed with the patent office on 2010-01-07 for combustion apparatus.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Emmanuel VJ Aurifeille, Robert A Hicks.
Application Number | 20100003624 12/453776 |
Document ID | / |
Family ID | 39707896 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100003624 |
Kind Code |
A1 |
Hicks; Robert A ; et
al. |
January 7, 2010 |
Combustion apparatus
Abstract
A combustor having an array of dilution holes it provided with
an asymmetrically located trim port for injection a controlled
volume of air into the combustor. The controlled volume mixes with
fuel rich air near the combustor wall and improves the dilution of
the combustion gases. The improved dilution reduces the formation
of NO.sub.x.
Inventors: |
Hicks; Robert A; (Derby,
GB) ; Aurifeille; Emmanuel VJ; (Derby, GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
ROLLS-ROYCE PLC
London
GB
|
Family ID: |
39707896 |
Appl. No.: |
12/453776 |
Filed: |
May 21, 2009 |
Current U.S.
Class: |
431/2 ;
431/190 |
Current CPC
Class: |
F23R 3/26 20130101; Y02E
20/34 20130101; F23R 2900/03042 20130101; F23R 3/06 20130101; Y02E
20/344 20130101 |
Class at
Publication: |
431/2 ;
431/190 |
International
Class: |
F23L 9/00 20060101
F23L009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2008 |
GB |
0812097.4 |
Claims
1. Combustion apparatus comprising a combustion envelope bounding a
combustion volume the combustion volume having an upstream end and
a downstream end, the combustion envelope having a plurality of
rows of dilution ports for the provision of dilution air which
mixes in use in a midstream flow with hot combustion gas from a
fuel injector, wherein each row extends in a circumferential
direction and is spaced from an adjacent upstream or downstream
row, the ports of each row being offset circumferentially from the
dilution ports of an adjacent row, characterised in that at least
one trim port is provided upstream of one or more of the rows of
dilution ports for supplying in use a flow of trim cooling air into
the combustion volume which mixes with hot combustion gas between
the midstream flow and an envelope cooling film attached to a wall
of the envelope.
2. Combustion apparatus according to claim 1, wherein the trim port
is sized to limit the degree of penetration of the trim cooling air
into the combustion volume.
3. Combustion apparatus according to claim 2, wherein the degree of
penetration is less than one third of half the radial height of the
combustion volume.
4. Combustion apparatus according to claim 1, wherein the trim port
is between 0.35 and 0.7 of the diameter of one of the dilution
ports.
5. Combustion apparatus according to claim 1, wherein the axis of
the trim port is located downstream and circumferentially offset
from a dilution port in one or more of the plurality of rows.
6. Combustion apparatus according to claim 1, wherein the trim port
is positioned to permit the flow of trim cooling air to be conveyed
by swirl within the combustor to a location downstream and
circumferentially aligned with a dilution port.
7. Combustion apparatus according to claim 1, wherein the
combustion volume is annular.
8. Combustion apparatus according to claim 1, wherein the
combustion envelope has a fuel injection location, wherein a
dilution port in the most upstream row is circumferentially aligned
with the fuel injection location and the trim port is associated
with the circumferentially aligned trip port.
9. Combustion apparatus according to claim 8, wherein the fuel
injection location is in an upstream wall of the combustion
envelope.
10. Combustion apparatus according to claim 8, wherein the
combustion apparatus has two rows of dilution ports.
11. A method of improving combustion within a combustion envelope
bounding a combustion volume the combustion volume having an
upstream end and a downstream end and the combustion envelope
having a plurality of rows of dilution ports, characterised in that
the method comprises providing a trim port wherein dilution air is
supplied through the dilution ports and mixed with hot combustion
gas in a midstream flow, wherein trim cooling air is supplied
through the trim ports and mixed with hot combustion gas upstream
of one or the rows of dilution ports and outside the midstream
flow.
12. A method according to claim 11, wherein swirl within the
combustor conveys the trim cooling air to a location downstream and
circumferentially aligned with a dilution port.
Description
[0001] This invention relates to combustion apparatus and
particularly combustion apparatus in which dilution air is supplied
to quench combustion products within a combustor.
[0002] Modern emission requirements set specific targets for the
amount of pollutants that may be ejected from combustion apparatus.
One undesirable pollutant is NO.sub.x. NO.sub.x is produced
particularly at high temperature conditions where there is a
slightly weaker than stoichiometric mixture of air and fuel.
[0003] It is an object of the present invention to seek to provide
an improved combustion apparatus giving reduced emissions.
[0004] According to a first aspect of the invention there is
provided combustion apparatus comprising a combustion envelope
bounding a combustion volume the combustion volume having an
upstream end and a downstream end, the combustion envelope having a
plurality of rows of dilution ports for the provision of dilution
air which mixes in use in a midstream flow with hot combustion gas
from a fuel injector, wherein each row extends in a circumferential
direction and is spaced from an adjacent upstream or downstream
row, the ports of each row being offset circumferentially from the
dilution ports of an adjacent row, characterised in that at least
one trim port is provided upstream of one or more of the rows of
dilution ports for supplying in use a flow of trim cooling air into
the combustion volume which mixes with hot combustion gas between
the midstream flow and an envelope cooling film attached to a wall
of the envelope.
[0005] Preferably the trim port is sized to limit the degree of
penetration of the trim cooling air into the combustion volume.
[0006] The degree of penetration is preferably less than one third
of half the radial height of the combustion volume.
[0007] The trim port may be between 0.35 and 0.7 of the diameter of
one of the dilution ports.
[0008] Preferably the axis of the trim port is located downstream
and circumferentially offset from a dilution port in one or more of
the plurality of rows.
[0009] Preferably the trim port is positioned to permit the flow of
trim cooling air to be conveyed by swirl within the combustor to a
location downstream and circumferentially aligned with a dilution
port.
[0010] The combustion volume may be annular.
[0011] Preferably the combustion envelope has a fuel injection
location, wherein a dilution port in the most upstream row is
circumferentially aligned with the fuel injection location and the
trim port is associated with the circumferentially aligned trip
port.
[0012] The fuel injection location may be in an upstream wall of
the combustion envelope.
[0013] Preferably the combustion apparatus has two rows of dilution
ports.
[0014] According to a second aspect of the invention there is
provided a method of improving combustion within a combustion
envelope bounding a combustion volume the combustion volume having
an upstream end and a downstream end and the combustion envelope
having a plurality of rows of dilution ports, characterised in that
the method comprises providing a trim port wherein dilution air is
supplied through the dilution ports and mixed with hot combustion
gas in a midstream flow, wherein trim cooling air is supplied
through the trim ports and mixed with hot combustion gas upstream
of one or the rows of dilution ports and outside the midstream
flow.
[0015] Preferably swirl within the combustor conveys the trim
cooling air to a location downstream and circumferentially aligned
with a dilution port.
[0016] The combustion apparatus may comprise a combustion envelope
bounding a combustion volume the combustion volume having an
upstream end and a downstream end, the combustion envelope having a
plurality of rows of dilution ports for the provision of dilution
air into the combustion volume, wherein each row extends in a
circumferential direction and is spaced from an adjacent row in a
direction perpendicular to the direction in which each row extends,
wherein the dilution ports of each row are offset circumferentially
from the dilution port of an adjacent row, characterised in that a
trim port is provided between the first row from the upstream end
and the second row.
[0017] Embodiments of the invention will now be described by way of
example only, with reference to the accompanying drawings, in
which:
[0018] FIG. 1 depicts a segment of an annular combustor in
accordance with the invention.
[0019] FIG. 2 depicts air flow through the dilution ports and trim
ports.
[0020] FIG. 1 depicts a portion of an annular combustor 2. The
combustor is used in conjunction with a fuel injector (not shown)
that introduces fuel into the upstream end of the combustor. The
fuel injector is preferably of the type known as a "rich burn"
injector which means that it although it uses air to atomise fuel
the majority of the air required for combustion is provided through
dilution ports 4, 6 on the radially inner and radially outer walls
of the annular combustor.
[0021] The walls of the combustor themselves are kept cool by a
film of air that is effusion fed onto the wall by anangled hole
that extends through the wall or a tile attached to the wall
depending on the architecture of the combustor. As the cooling air
is fed to the wall at an angle the air attaches to the wall to form
a film that isolates the wall from hot combustion gases. The film
is thin and remains attached to the wall till it is replenished by
a new film from effusion cooling holes further downstream. Although
the volume of air used for wall cooling is relatively small, once
the film detaches from the wall it mixes with hot combustion gases
and can help lower the temperature of the main gas flow through the
combustor.
[0022] A plurality of fuel injectors are mounted to the head end of
the combustor and are circumferentially spaced from one another at
a uniform spacing.
[0023] The dilution ports 4, 6 are also arranged in
circumferentially extending rows with the ports through the
radially inner wall and the radially outer walls being axially and
circumferentially aligned. The ports in each row are equally spaced
and the ports of adjacent rows are offset circumferentially by half
the port pitch. There are twice as many dilution ports (per row) as
there are injectors, with the arrangement being that the first row
of dilution ports spaced from the injector has half its dilution
ports arranged to be circumferentially aligned with the axis 8 of
the injectors with the remaining half to be circumferentially
intermediate the injector axes.
[0024] Accordingly, the configuration of ports results in a series
of discreet currents of air 10, 12 that penetrate into the
combustion space. The flows coalesce 14 near the central region of
the combustor when measured between the radially inner and radially
outer walls such that the partially combusted, fuel rich mixture
coming from the injectors is diluted and further mixed with air
flowing through the first (primary) row of ports and then further
diluted and mixed with air flowing through the second (secondary)
row of ports. The combustion products can be diluted in a
controlled manner along the length of the combustor in order to
minimise both smoke emissions and NO.sub.x production.
[0025] The streams of air entering the combustor through the
dilution ports have a relatively high momentum ratio so that they
can penetrate to the combustor's mid stream. This maximises rapid
dilution of the hot, fuel rich mixture in the central region of the
combustor but the strong currents of cooling gad flowing through
the dilution ports at a position close to the combustor walls
interact poorly with the hot gas in this region. Poor interaction
can result in little dilution in the axial plane which can persist
downstream as streaks of hot gas that subsequently promotes
NO.sub.x formation in the combustor. The hot streaks also
contribute to an increase in the near wall radial temperature
profile at the combustor exit. Since the combustion gases are fed
directly to the turbines significant air is required to control the
temperature to maintain a high turbine life.
[0026] To improve the mixing of the fuel rich gases between the
midstream flow and the cooling film attached to the walls of the
combustor a trim ports 18 are provided. As minimum NO.sub.x
formation is typically required, both the radially inner and
radially outer combustor walls are provided with trim ports to
enable mixing both in radially inner and radially outer
locations.
[0027] The function of the trim port is to introduce a controlled
amount of air 16 into the combustion volume in the vicinity of the
combustor walls between the boundary cooling film and the
combustor's midstream that is diluted by the dilution air entering
the combustor through the dilution ports 4, 6. This is typically a
region from the wall cooling film to up to a third of half the
combustor height. The relatively small volume of air entering
through the trim port does not have the momentum required for it to
penetrate to the centre of the combustor and is therefore fed to
the near wall vicinity of the combustor to dilute and cool the hot
gases at this location.
[0028] The degree of penetration of the air and the placement of
its injection into the combustion volume is important as it
controls the impact the air has on reducing local gas temperature.
If the penetration is too strong the jet will penetrate too deeply
into the combustor volume and merge with the main primary port flow
as it mixes out in the mid-section of the combustor. If the
penetration is too weak then the trim flow will be absorbed into
the near wall cooling film and not contribute to dilution until
much further downstream.
[0029] It is desirable that the trim port is located close to the
primary ports which are preferably at the same circumferential
location as the fuel injectors. The exact location of the trim port
will depend on the specific application and combustor geometry. The
lower momentum of the air entering through the trim port enables
swirl in the combustor to carry the air that entered through the
trim port circumferentially as it passes axially down the
combustor. Thus the swirl can carry the trim port air to pass
downstream of the first row dilution port that lies directly in
front of the fuel injector.
[0030] The optimum mixing point for the trim port air to mix with
the hot gas outside the core flow is just upstream of and between
the secondary ports.
[0031] For an annular combustor the location for the trim port is
typically found on a line prescribed from a point between adjacent
primary ports and the point at which the projected injector axis
crosses the circumferential line midway between the centre of the
primary port row and the centre of the secondary port row. Because
the trim port air requires a short axial distance to mix and spread
the trim port is preferably located either at the same axial
spacing as the first row of dilution ports or just downstream of
these ports.
[0032] Although the trim ports can be located upstream of the
primary dilution ports and still permit the swirl to carry the
input air to the desired mixing location there is a danger that the
input air may become fouled within the dilution air which will
adjust its path and can result in the trim air being entrained in
the core flow and failing to provide cooling to the hot gas in the
near wall area. A greater than desirable circumferential spacing
between the trim port and primary dilution port may be required to
ensure such entrainment does not occur.
[0033] It will be appreciated that where the swirl direction is in
a different direction the line 20 may be a mirror of its marked
position when reflected about the injector axis. A different swirl
direction may be achieved by different fuel injector
architectures.
[0034] Preferably the trim port diameter is between 0.35 and 0.7 of
the diameter of the corresponding primary port.
[0035] In addition to a direct impact on NO.sub.x control through
reducing near wall gas temperatures, the invention is also of
assistance by improving the homogenisation of the near wall radial
temperature profile at the combustor exit. The more homogeneous
temperatures allow the amount of air used at this location to be
reduced when compared with similar combustors without the trim
port. This reduction in the use of air at this point allows it to
be input into the combustor further upstream where it will have a
greater effect on NO.sub.x formation.
[0036] Although the invention has been described with respect to
annular combustors it is equally applicable to can, or other forms
of combustors having dilution ports.
* * * * *