Patent Application
20090049894
This application claims the benefits of British application No. 07016386.0 filed Aug. 21, 2007 and is incorporated by reference herein in its entirety.
The present invention relates to a device and a method for monitoring a flame in a combustion chamber. Especially, it relates to a temperature measurement arrangement for use in a burner of a gas turbine engine.
A gas turbine engine usually comprises a compressor, a combustion chamber and a turbine. The compressor delivers compressed air for use in the combustion chamber. In the combustion chamber a mixture of air and fuel is combusted by means of a burner in order to produce a hot gas stream which drives the turbine. Typically one or more burners are used. In this context it is important to monitor the flame to avoid instabilities of the combustion process. Therefore, it is desired to detect the presence of the flame and the intensity of the heat release rate from the flame. The heat release rate is an indication of the intensity of the chemical reaction and the stability of the flame.
It is an objective of the present invention to provide a method for monitoring a flame in a combustion area like, e.g., a combustion chamber. It is a further objective of the present invention to provide a burner which allows the monitoring of a flame in a combustion zone. It is another objective of the present invention to provide a gas turbine comprising a burner which allows the flame to be monitored. It is a still further objective of the present invention to provide an internal combustion engine which allows the monitoring of a temperature in a cylinder.
The first objective is solved by a method for monitoring a flame in a combustion chamber as claimed in the claims. The second objective is solved by a burner and the third objective is solved by a gas turbine as claimed in the claims. The still further objective is solved by an internal combustion engine. The depending claims define further developments of the invention.
The inventive method for monitoring a flame relates to a combustion chamber which comprises a wall with an inner side and an outer side. While the inner side shows towards the flame in the interior of the combustion chamber, the outer side shows away from the interior and the flame. The method is characterised in that the radiation which is emitted from a part of the outer side of the wall is optically detected by a sensor. The wall of the combustion chamber is heated up depending on the existence and the temperature of a flame inside the combustion chamber. Due to the increased temperature the wall, or especially a particular part of the wall, emits radiation which generally can be detected optically. This is used by the inventive method, wherein the black body radiation from the surface of the combustion chamber is detected based on an optical measurement. This method has the advantage that it is unaffected by rapid changes in temperature. Comparable devices using thermocouples would be likely to fail due to their fragility.
The heat release rate and/or the temperature of the part of the outer side of the wall can be determined by means of the detected radiation. The temperature of the wall provides information regarding the existence and the intensity of the heat release rate from the flame inside the combustion chamber. The heat release rate is an indication of the intensity of the chemical reaction and the stability of the flame.
Generally, the mentioned wall of the combustion chamber may be the actual wall of the combustion chamber. However, it may as well be a wall section of a device attached to the combustion chamber such as, for example, a wall section of a burner. In this case the outer side of a wall section of the burner is to be regarded as a part of the outer side of the combustion chamber in the context of this invention.
The used sensor may, for instance, be a photodiode. Preferably the detected radiation can be focussed on the sensor. In particular, the detected radiation may be focussed by means of an optical lens. A focussing of the emitted radiation reduces the influence of radiation which is not emitted from the desired part of the outer side of the wall of the combustion chamber. This further increases the accuracy of the measurement.
Preferably, the emitted radiation can be detected from the part of the outer side of the wall which is situated opposite a part of the inner side of the wall which is exposed to the flame. In this case the flame directly heats up the inner side of the wall and the heat is transported through the wall to the outer side of the wall by thermal conduction. Hence, the temperature of the outer side of the wall is directly related to the characteristics of the flame inside the combustion chamber. The black body radiation from the outer side of the wall due to the increased temperature can be detected and can be used to determine the temperature of the outer side of the wall. Hence, also temperature of the flame inside the combustion chamber can be determined.
Advantageously, the emitted radiation can be detected from the bottom of a hole in the wall which extends from the outer side of the wall towards the inner side of the wall. At the bottom of a hole the thickness of the wall, which is the distance between the inner and the outer side of the wall, is smaller than at other parts of the wall. This provides very effective and fast heat conduction between the inner and the other side of the wall.
The inventive burner, which is suitable for monitoring the flame in the combustion zone of a combustion chamber, comprises a wall section with an inner side which shows towards a combustion zone, and an outer side which shows away from the combustion zone. It further comprises a sensor for optically detecting the radiation emitted from the outer side of said wall section. This avoids the use of thermocouples which may be very fragile. Preferably, the used sensor is a photodiode. In particular, the burner may further comprise an element to focus the emitted radiation to the sensor. This element may be, for instance, an optical lens. A focussing of the emitted radiation increases the accuracy and sensitivity of the measurement. Furthermore, it reduces the influence of radiation which is not emitted from the outer side of said wall section of the burner.
Advantageously, said wall section forms the bottom of a hole extending from the outer side towards the inner side. The sensor can then be positioned such that it detects the radiation emitted from the bottom of said hole. The sensor may be located at a distance of the bottom of the hole. Moreover, the hole can be evacuated or filled with an inert gas. For instance nitrogen gas may be used. An evacuated or inert gas filled hole protects the sensor, especially the surface of the sensor. Furthermore, it reduces the oxidation of the surface of the bottom of the hole.
In particular, the sensor can be positioned in the burner such that it can detect the radiation emitted from the outer side of a part of the wall, the corresponding inner side of which is exposed to the flame. In the case said part of the wall, from which the emitted radiation is detected, is rather thin the detected radiation provides nearly direct information about the temperature of the flame itself.
The hole and the sensor can especially be positioned in the burner such that it detects the radiation emitted from the outer side of a part of the wall, the corresponding inner side of which is located near the base of the flame. The base of the flame is defined by the location of the attachment of a low pressure region generated by a swirling mix of air and fuel. The detection of the radiation emitted from a region located near the base of the flame provides information about the characteristics of the flame.
The burner may further comprise a light emitting diode to determine the state of the sensor. Especially the state of the photodiode can be auto checked by fitting a light emitting diode to a part of the photodiode's surface. In this case, the photodiode's response to the light emitting diode determines the state of the sensor prior to the starting of the machine fitted with this sensor.
The inventive gas turbine comprises an inventive burner, as previously described. It also has the mentioned advantages.
The still further objective is solved by an internal combustion engine, comprising at least one cylinder with a wall section having an inner side which shows towards a combustion zone, and an outer side which shows away from the combustion zone. The internal combustion engine further comprises a sensor for optically detecting the radiation emitted from the outer side of said wall section. The design of said wall section and the sensor can be the same as in the inventive burner.
The inventive internal combustion engine allows for monitoring the cylinder(s) over a period of time, thereby enabling the monitoring of the average flame temperature or average fuel/air mix etc. This is most suitable for diesel engines at fixed revolutions per minute for periods of time.
Further features, properties and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings.
An embodiment of the present invention will now be described with reference to
The combustor comprises in flow series a burner with a swirler portion 3 and a burner-head portion 11 attached to the swirler portion 3, a transition piece being referred as combustion pre-chamber 5 and a main combustion chamber 9. The main combustion chamber 9 has a diameter being larger than the diameter of the pre-chamber 5. The main combustion chamber 9 is connected to the pre-chamber 5 via a dome portion 30. In general, the transition piece 5 may be implemented as a one part continuation of the burner towards the main combustion chamber 9, as a one part continuation of the main combustion chamber 9 towards the burner, or as a separate part between the burner and the main combustion chamber 9.
The burner comprises a radial swirler 3 and a head plate 11 to which the swirler 3 is fixed. The head plate 11 is fixed to an outer casing 10 of the combustor. The burner-head plate 11 comprises a removable assembly 13 which is situated in the middle of the burner-head plate 11, as indicated by the centre line 27.
The radial swirler 3, the pre-chamber 5 and the main combustion chamber 9 show radial symmetry about a centre axis or centre line 27. A flow channel 28 for feeding compressor air into the burner is situated between the outer casing 10 and the radial swirler 3, the pre-chamber 5 and the main combustion chamber 9.
Compressed air 24 flows in the direction of the arrows 1 through the flow channel 28 towards the burner-head plate 11. When arriving at the burner-head plate 11 the compressed air 24 turns about 90° so as to enter the radial swirler 3, as indicated by arrows 2. The swirler 3 comprises a plurality of vanes which are arranged in a circle and flow slots being defined between adjacent vanes in the circle. The compressed air flows through the slots into the prechamber 5, as indicated by arrows 4. Fuel is introduced into the air flowing through the slots by fuel nozzles located in the vanes. The swirler 3 therefore provides a swirling mixture of air and fuel.
Moreover, the slots are inclined with respect to the combustor's radial direction so that a swirl is generated in the fuel-air-mixture 6 when entering the pre-chamber 5. In doing so the compressed air generally flows in the direction indicated by arrows 6, thereby forming the swirling air-fuel-mixture 6. The air-fuel-mixture 6 flows in the direction as indicated by arrows 8 through the pre-chamber 5 into the main combustion chamber 9 where it combusts.
In
The removable assembly 13 further comprises a blind hole 18 which is located in the centre of the removable assembly 13 along the centre line 27. Alternatively, the blind hole 18 may be positioned in the removable assembly parallel to the centre line 27, but not in the centre of the removable assembly 13. The blind hole 18 extends through the cover plate 26 and through a major part of the plug 25. The bottom 17 of the blind hole 18 has a relatively small distance 22 to the inner surface 21 of the removable assembly 13. While the inner surface 21 shows towards the flame, i.e. towards the interior of the combustion chamber, the surface of the bottom 17 of the hole 18 shows away from the interior of the combustion chamber and can thus be regarded as an outer surface of the burner as seen from the interior of the combustion chamber. Hence, the bottom 17 of the hole 18 forms a wall section with inner side 21 which shows towards a combustion zone, and an outer side which shows away from the combustion zone.
Moreover, the removable assembly 13 comprises a pipe fitting 14, a tube extension piece 15 and an embedded photodiode 16. The pipe fitting 14 is connected to the cover plate 27. Moreover, the pipe fitting 14 connects the removable assembly 13 to the tube extension pieca—5_aNd_the embedded photodiode 16. A bore 31 extends entirely though the pipe fitting 14 and the extension piece 15 and is aligned with the blind hole 18. The photodiode 16 is fixed to the end of the tube extension piece 15 and closes the bore 31.
The hole 18 is concentric to the bore of the pipe fitting 14, such as a Swagelock fitting. The length of the blind hole 18, the pipe fitting 14 and the tube extension piece 15 are such as to provide a collimated viewing angle from the photodiode's sensor to the bottom of the blind hole 17.
The blind hole 18 is formed in the removable assembly 13 with a flat bottom face 17. The hole 18 may be reamed flat to a distance 22 to the inner surface 21 of the removable assembly. The distance 22 is specified by the material properties of the assembly 13 in such a way as to provide an optimal heat transfer from the inner surface 21 of the removable assembly 13 to the bottom 17 of the hole 18.
During operation of the burner the inner surface 21 is exposed to the base of a flame 23. This increases the temperature of the inner surface 21 and, through thermal conduction, also the temperature at the surface of the bottom 17 of the blind hole 18 raises. When this occurs the surface of the bottom 17 radiates electromagnetic radiation which the photodiode 16 is sensitive to. Radiation from the surrounding walls of the hole do not interfere substantially with the photodiode 16 since the length of the hole 18, the pipe fitting 14 and the tube extension piece 15 collimates the viewing angle such that the electromagnetic radiation from the bottom of the hole 17 dominates the radiation seen by the photodiode 16.
The sensitivity of this configuration may be enhanced through the use of an optical lens 19 or other focusing means, which may be mounted as indicated by lens 19 in
The removable assembly 13 may be additionally equipped with a gas filling port 20, as it is shown in
In the embodiment shown in
The flame inside the combustion chamber heats up the inner surface 21 of the removable assembly 13. The heat is transferred through the wall and heats up the bottom 17 of the blind hole 18. Due to its increased temperature the bottom 17 emits electromagnetic radiation. This radiation propagates through the hole 18 and is detected by the photodiode 16. The results of this measurement can be used to determine the temperature of the bottom of the hole 17. By taking into account the distance 22 and the heat transfer coefficient of the material of the plug 25 also the temperature of the flame inside the combustion chamber and the heat release rate can be determined.
The speed of response of the measurement to changes in the flame temperature at the inner surface 21 of the removable assembly 13 is dependent on the heat transfer coefficient of the assembly 13, in particular of the material of the plug 25, and the distance 22. The heat transfer coefficient and the distance 22 can be adjusted by using a separate bottom plate 29 as wall between the hole 118 and the inner side of the burner. In this case, the hole is not a blind hole but a through hole 118 which is closed to the interior of the combustion chamber by the bottom plate 29. This alternative solution is shown in
When the bottom plate 29 is detachably fixed to the plug 25 the heat transfer characteristics can be changed just by exchanging the bottom plate for another bottom plate with, for example, a different thickness and/or different material characteristics. The use of a separate bottom plate 29 made of a suitable material therefore allows for individual adjustment of the heat transfer coefficient and the distance 22 dependent on the requirements of the particular burner and the used sensor 16. The adjustment is independent of the characteristics of the material of the plug 25.
Of course, all described variations and alternatives can be combined. For example, an inventive removable assembly can comprise a bottom plate 29, a lens 19 and one or more gas filling ports 20. Generally, the sensor is a seal unit and as a result the optical system is not compromised by water washing of the machine's compressor.
Although a specific location of the removable assembly 213 is shown in
In summary, the invention provides the possibility to monitor a flame inside a combustion chamber or a cylinder by optical means.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07016386.0 | Aug 2007 | GB | national |
