Abstract:
A method for monitoring a flame in a combustion chamber comprising a wall with an outer side is provided, wherein the radiation which is emitted from a part of the outer side of the wall is optically detected by a sensor. Furthermore, a burner is provided, especially for use in a gas turbine. The burner comprises a wall section with an inner side, which shows towards a combustion zone, and an outer side. The burner further comprises a sensor for optically detecting the radiation emitted from the outer side of said wall section.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefits of British application No. 07016386.0 filed Aug. 21, 2007 and is incorporated by reference herein in its entirety. 
   FIELD OF INVENTION 
   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. 
   BACKGROUND OF THE INVENTION 
   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. 
   SUMMARY OF INVENTION 
   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&#39;s surface. In this case, the photodiode&#39;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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. 
       FIG. 1  schematically shows a part of a combustor for a gas turbine engine in a sectional view. 
       FIG. 2  schematically shows the location of the flame in the combustor, which is shown in  FIG. 1 , in a sectional view. 
       FIG. 3  schematically shows a removable assembly of the burner, where the sensor is located, in a sectional view. 
       FIG. 4  schematically shows the removable assembly which is shown in  FIG. 3  with an additional lens arrangement. 
       FIG. 5  schematically shows the removable assembly which is shown in  FIG. 3  with an additional feature to enable the sensor to be filled with inert gases. 
       FIG. 6  schematically shows a part of a removable assembly in a sectional view. 
       FIG. 7  shows a cylinder of an internal combustion engine in a top view. 
       FIG. 8  shows a first section through the cylinder. 
       FIG. 9  shows a second section through the cylinder. 
   

   DETAILED DESCRIPTION OF INVENTION 
   An embodiment of the present invention will now be described with reference to  FIGS. 1 to 6 .  FIG. 1  schematically shows a part of a combustor of a gas turbine engine in a sectional view. 
   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 pre-chamber  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&#39;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. 
     FIG. 2  schematically shows the location of the flame in the described combustor in a sectional view. One can see in  FIG. 2  the burner-head plate  11 , the radial swirler  3 , the pre-chamber  5  and the main combustion chamber  9 . The burner-head plate  11  comprises a removable assembly  13 . The combusting mixture of air and fuel forms a flame which follows the region of low pressure  12 . The base of the low pressure region  12 , which defines the base of the flame  23 , is attached to the inner side  21  of the removable assembly  13 . 
   In  FIG. 3  the removable assembly  13  is schematically shown in a sectional view. The removable assembly  13  comprises a plug  25  and a cover plate  26 , which is connected to the plug  25 . The plug  25  is an element which fits into a central hole in the burner-head plate  11  and the cover plate  26  is used to fix the removable assembly  13  to the burner-head plate  11 . 
   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&#39;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  FIG. 4 .  FIG. 4  schematically shows a respective variant of the removable assembly  13  of  FIG. 3  in a sectional view. The optical lens  19  is mounted inside the bore  31  between the pipe fitting  14  and the tube extension piece  15 . In this configuration the lens  19  is located such that the focal point of the lens  19  is located on the surface of the bottom  17  of the blind hole  18 . The use of a focussing lens increases the accuracy and the sensitivity of the measurement. 
   The removable assembly  13  may be additionally equipped with a gas filling port  20 , as it is shown in  FIG. 5 .  FIG. 5  schematically shows a respective variant of the removable assembly  13  of  FIG. 3  in a sectional view. In this variant of the embodiment, the hole  18  is connected to a filling port  20  which is, in the present embodiment, a gas filling port. Of course, it is possible to equip the removable assembly  13  with more than one gas filling port  20 . Especially in the case that a lens  19  inside the hole  18  is used, it may be useful to equip the removable assembly  13  with two or more gas filling ports  20  to provide accesses to the parts of the hole  18  on both sides of the lens  19 . If only one gas filling port is present in a variant with a lens the gas filling port would be located between the lens and the cover plate  26 . 
   In the embodiment shown in  FIG. 5 , the gas filling port  20  is connected to the tube extension piece  15  since no lens is present. It comprises a flow channel which is connected to the bore  31  and may be used to evacuate the bore  31  and the blind hole  18  or to fill the bore  31  and the blind hole  18  with a gas. The filling gas may be an inert gas, for instance nitrogen. This reduces the oxidation of the surface of the bottom  17  of the blind hole  18 . Alternatively, the blind hole  18  may also be filled with a suitable liquid. 
   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  FIG. 6  which shows a part of the removable assembly  13  in a sectional view. One can see the plug  25  and a part of the cover plate  26 . The plug  25  and the cover plate  26  comprise the through hole  118 . At the side of the plug, which forms the inner surface  21  of the removable assembly  13 , the hole  18  is closed by the bottom plate  29 . The distance  22  is now determined by the thickness of the bottom plate  29 . The bottom plate  29  is fixed to the plug  25 , for instance by welding, soldering or a detachable connection. 
   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&#39;s compressor. 
     FIGS. 7 to 9  show a cylinder of an internal combustion engine with a removable assembly  213  which allows for monitoring the temperature inside the cylinder. While  FIG. 7  shows a top view onto the cylinder  200 ,  FIGS. 8 and 9  show cuts through the cylinder taken in mutually perpendicular directions. 
     FIG. 8  shows a section through the cylinder  200  in which a cylinder wall  202 , the inlet and outlet valves  204 ,  206 , respectively, the spark plug  208  and a piston  210  are partly shown.  FIG. 9  shows a section through the cylinder  200  which is perpendicular to the section shown in  FIG. 8 . The relation between the two sections is shown in  FIG. 7 . The removable assembly  213  is located in the cylinder head  212  beside the spark plug  208 . The arrangement of the spark plug  208 , the valves  204 ,  206  and the removable assembly  213  can be best seen in  FIG. 7 . The design of the removable assembly can be the same as has been described with respect to  FIGS. 3 to 6  in conjunction with the gas turbine burner. 
   Although a specific location of the removable assembly  213  is shown in  FIGS. 7 to 8 , other locations are also possible as long as the location allows for placing the removable assembly such as to show towards the flame in the cylinder. 
   In summary, the invention provides the possibility to monitor a flame inside a combustion chamber or a cylinder by optical means.