Abstract:
In a method for igniting the combustion chamber of a gas turbine unit, a safely working ignition and a long lifetime of the ignition device ( 10 ) is achieved by discharging a compressed gas with a supercritical pressure ratio through a nozzle ( 21 ) and heating it up to a temperature sufficient to ignite hydrocarbons by interacting with a resonance tube ( 19 ) arranged behind said nozzle ( 21 ), and using said heated-up gas to directly or indirectly ignite a fuel/air mixture introduced into said combustion chamber.

Description:
This application is a Continuation of, and claims priority under 35 U.S.C. § 120 to, International application number PCT/CH03/00133, filed 21 Feb. 2003, and claims priority under 35 U.S.C. § 119 to German application number 102 11 141.3, filed 14 Mar. 2002, the entireties of both of which are incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns the field of gas turbines. It concerns a method for igniting the combustion chamber of a gas turbine unit and an ignition device for carrying out the method. 
   2. Brief Description of the Related Art 
   The continuous combustion in the combustion chamber of a gas turbine is initiated when an external ignition source ignites the combustion mixture (usually an air/fuel mixture). Usually this is accomplished with electric sparks that ignite the mixture in the combustion chamber either directly or indirectly using a so-called pilot burner. Alternative ignition sources provide the required energy via a glowing surface or a laser light source. The ignition plug for generating the ignition spark requires high electric voltage directly in the combustion chamber. The supply line, especially the isolation of this high voltage line that must be comprised of ceramics due to the existing temperatures at the compressor exit, is relatively susceptible to heat expansion and vibrations. This is why such ignition systems are comparatively sensitive and must be replaced relatively often during the life of a gas turbine. This could result in low availability of the unit. The other known ignition by way of an auto-ignition avoids the supply of high voltages; however, the ceramic glow element itself currently does not have a long enough lifecycle. 
   In a completely different technical field, i.e., in military applications, it is necessary to initiate a chemical reaction with very simple, robust devices. This led to the development of so-called Resonance Igniters that utilize the heating of gas for ignition purposes with the gas supercritically dissipating its pressure energy into heat in a resonance tube. Usually solid reaction mixtures or—using a H 2 /O 2  and/or H 2 /air ignition flame—other fuels are being ignited (ref. for example U.S. Pat. Nos. 3,994,232 or 5,109,669). 
   SUMMARY OF THE INVENTION 
   The aspect of the invention includes a method for igniting the combustion chamber of a gas turbine unit as well as an ignition device for carrying out the method that avoids the disadvantages of known methods and devices and that is characterized by a simple and sturdy design, a high level of availability and operational safety, the absence of electric devices and easy integration into existing units. 
   A principle of the present invention is to use the known resonance ignition for igniting the combustion chamber of a gas turbine unit in which a compressed gas with a supercritical pressure ratio is discharged through a nozzle and, interacting with a resonance tube arranged behind the nozzle, is heated up to a temperature that is suitable for igniting carbon hydroxide and in which the heated-up gas is used directly and/or indirectly for igniting the fuel/air mixture introduced in the combustion chamber. 
   In a preferred embodiment the combustion chamber comprises a combustion space to which a flame tube of a pilot burner is connected that discharges into the combustion space of the combustion chamber. Ignition fuel and ignition air are introduced into the flame tube and the ignition fuel/ignition air mixture is ignited in the flame tube. 
   It is possible to use different gases for the resonance ignition. The preferred compressed gas is air because it does not require any additional heating up of the gas. 
   If the compressed gas used is something other than air, especially nitrogen, ignition air is used for the ignition and the ignition air requires heating up. 
   In accordance with a preferred embodiment of the invention an ignition space that leads into the flame tube is arranged between the flame tube and the resonance tube. When part of the air that is heated in the resonance tube is supplied to the ignition space through an ignition opening in the resonance tube, it is mixed with the ignition fuel in the chamber and ignites. The remaining part of the discharged air in the resonance tube preferably is removed passed the ignition space into the flame tube. 
   Alternatively it is possible for the ignition fuel/ignition air mixture in the flame tube to be ignited when it comes into contact with a heated surface of the resonance tube. 
   It also is possible for the entire decompressed air in the resonance tube to be used for igniting the ignition fuel/ignition air mixture. 
   The method in accordance with the invention is especially easy to implement when the already present fuel in the gas turbine is being used as ignition fuel. 
   However, it also is possible to use an ignition fuel that is different from the fuel in the gas turbine, especially methane or propane. 
   Ignitability can be improved if oxygen is added to the air that is heated up in the resonance tube and/or to the remaining air that is discharged in the resonance tube. 
   It is especially easy to integrate the method in a gas turbine unit with a compressor for compressing the combustion air when the compressed air for igniting the combustion chamber is removed from the compressor and/or an external ignition air supply. 
   The ignition device in accordance with the invention preferably is designed so that a flame tube is connected to the combustion space of the combustion chamber and that at least part of the gas that is discharged through the nozzle into the resonance tube flows into the flame tube through an exit channel arranged outside the resonance tube. 
   In a further development of this embodiment the entire gas discharged through the nozzle into the resonance tube flows through the exit channel outside the resonance tube whereby a heated surface of the resonance tube is adjacent to the flame tube. 
   In a further development of this embodiment the resonance tube is adjacent to an ignition chamber which in turn flows into the flame tube. A part of the gas in the resonance tube flows directly from the resonance tube into the combustion chamber through an ignition opening. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail using exemplary embodiments in connection with the drawing, with the figures showing the following: 
       FIG. 1  parts of a longitudinal section of a first preferred exemplary embodiment of an ignition device in accordance with the invention with an ignition space being arranged between flame tube and resonance tube in which directly heated gas exits from the resonance tube; 
       FIG. 2  in a presentation comparable to  FIG. 1  a second exemplary embodiment of an ignition device in accordance with the invention in which the resonance tube with a heated surface is directly adjacent to the flame tube; 
       FIG. 3  a device scheme for the supply of compressed air to an ignition device in accordance with the invention that is arranged in a gas turbine unit; 
       FIG. 4  in a presentation comparable to  FIG. 1  a third exemplary embodiment of an ignition device in accordance with the invention in which the resonance ignition is arranged inside a modified ignition torch and 
       FIG. 5  in a presentation comparable to  FIG. 1  another exemplary embodiment of an ignition device in accordance with the invention in which the resonance tube is directly connected to the fuel tube. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows parts of a longitudinal section of a first preferred exemplary embodiment of an ignition device in accordance with the invention. The ignition device  10  is based on a configuration that is described in FIG. 1 of EP-A1-0 992 661. The hot gasses required for driving the gas turbine are generated by combusting a gaseous and/or liquid fuel in combustion space  11  of a combustion chamber ( 30  in  FIG. 3 ). The combustion space  11  has a lateral combustion space wall  12 . A flame tube  13  discharges into the combustion space  11  through an opening in the combustion space wall  12 . In the illustrated example the flame tube  13  is concentric as it relates to a central axis  14 . Fuel is introduced to the flame tube  13  through a central fuel tube  23 . 
   While in the device according to FIG. 1 of EP-A1-0 992 661 combustion air is introduced into the flame tube through an air supply ( 70 ) that concentrically surrounds the fuel tube ( 23 ) and an ignition electrode ( 51 ) is arranged for the ignition that protrudes into an ignition space ( 50 ) that is filled with air and fuel from the fuel tube and the air supply via connecting channels ( 55 ,  56 ), the (sensitive) electric ignition is replaced with a robust resonance ignition in the ignition device  10  according to  FIG. 1  of the present application. 
   The object of the invention is to increase the availability of the gas turbine by providing a robust ignition lance without any electric components. The resonance ignition is based on the following principle: If a compressed gas (e.g. air) is discharged through a nozzle, the gas initially cools off since the pressure energy is converted to kinetic energy. If, however, it is discharged with an exceedingly supercritical pressure ratio, the pressure inside the gas is much higher than in the surroundings. This leads to post expansions that discharge the pressure to ambient pressure through compression waves. These compression waves dissipate strongly, i.e. the existing pressure energy is converted to heat. If the flow is decelerated as well, the kinetic energy is also available in the form of heat. This means the largest part of the original pressure energy can be converted to heat. 
   In the ignition device  10  of  FIG. 1  the concentric external air supply is interrupted. Air in an ignition gas tube  22  that runs parallel to the fuel tube  23  is discharged through a nozzle  21  (can also be a Laval nozzle) before it reaches the flame tube. In the space behind the nozzle a resonance tube  19  is arranged in the symmetry axis  15  of the ignition device with the tube being open towards nozzle  21 . The gas (air) that flows from the nozzle  21  directly reaches the resonance tube  19 . By designing the resonance tube  19  accordingly that is arranged directly at the exit of nozzle  21  it is possible to generate strong temperature increases at the opposite end of the resonance tube  19  that is partially or completely closed. For ignition purposes a small part of the air (ignition air) that is injected into the resonance tube is heated up to above the ignition temperature of hydrocarbons. This ignition air is supplied to a subsequent, separate ignition space  16  arranged between resonance tube  19  and flame tube  13  through a small ignition opening  20  of the resonance tube  19 . Here it is mixed with fuel and ignites. The remaining discharged air is removed parallel to the resonance tube  19  and the ignition space through an exit opening  17  and an exit channel  18 . However, it is possible to use the remaining air and/or all of the supplied air for igniting the mixture. If compressed air is used as resonance gas, pressure in excess of 10 bar is required to reach the ignition temperature. It is therefore suggested to supply air with pressure around 10 bar (or more) and to heat them to ignition temperature by way of a resonance tube. 
   The fuel of the gas turbine is to be mainly used as ignition fuel. An alternative is to use other fuels such as methane or propane, for example, that are currently in use. 
   In the ignition device  24  shown in the exemplary embodiment of  FIG. 2  the end of the resonance tube  19  that is opposite the nozzle  21  is completely closed. There is no ignition space so that the closed end of the resonance tube  19  and its heated surface are in direct contact with the gas in the flame tube  13 . The entire air that is discharged through nozzle  21  is removed through the exit opening  17  and the exit channel  18  into the flame tube  13 . In addition, oxygen  26  can be added to the ignition gas tube  22  and into the exit channel  18  by means of an oxygen channel  25 . 
   According to  FIG. 3  the ignition device  31  can easily be integrated into a gas turbine unit  27 : The gas turbine unit  27  comprises a compressor  28  for compressing the combustion air that is supplied via the combustion air inlet, a combustion chamber  30  and a gas turbine  29  in which the hot gasses from the combustion chamber  30  are discharged and then are supplied to an exhaust gas outlet  39  to a flue or waste heat steam generator. Depending on the compressor pressure of the gas turbine  29  the air can be supplied via the gas turbine  29  itself and/or via the external ignition air supply  35 . From the two alternative sources the compressed air is supplied to an ignition air storage  34  via check valves  36 ,  37  and from there it can be fed, as needed, into the ignition device  31  via a valve  33 . The necessary ignition fuel is provided via an ignition fuel supply  32 . The required resonance heating can be accomplished with a propellant other than air (e.g. N 2 ) if this is more readily available. In this case, however, the necessary ignition air must also be heated. This can be accomplished through a hot surface or a mixture of heated propellant or a part of it. 
   The ignition by means of the heated up surface of the resonance tube ( FIG. 2 ) is also possible when air is used as a propellant. Ignitability can be improved when oxygen is added to the resonance gas and/or into the remaining discharged air that is to be dissipated. 
   In principle the described method can be integrated into different geometires. Due to its compact design, however, it is especially advantageous to design the resonance tube  19  such that the currently electric component (FIG. 1 of EP-A1-0 992 661) is simply replaced with the resonance tube with compressed air supply  21 ,  22 . Analogous to  FIGS. 1 and 2  it is possible to use a resonance ignition device comprising a resonance tube  19 , nozzle  21  and ignition gas tube  22  according to  FIG. 4 . The resulting ignition device  40  can be integrated into a common ignition gas flare. The remaining discharged air that is not introduced into the ignition space  16  through the ignition opening  20 , reaches an exit chamber  42  via an exit opening  41  and from there reaches the flame tube  13  through a connecting channel  43 . 
   In the exemplary embodiment in  FIG. 5  fuel is added through a comparatively narrow connecting channel  46  from the fuel tube  23  to the air that is discharged through nozzle  21  and heated in the resonance tube  19 . The resulting mixture is ignited and exits from ignition openings  45  on the closed side of the resonance tube  19  into the flame tube  13  and results in the ignition of the fuel/air mixture in the flame tube  13 . 
   List of Reference Numerals 
     10 , 24 , 40 , 44  ignition device 
     11  combustion space 
     12  combustion space wall 
     13  flame tube 
     14  central axis (ignition device) 
     15  symmetry axis 
     16  ignition space 
     17 , 41  exit opening 
     18  exit channel 
     19  resonance tube 
     20 , 45  ignition opening 
     21  nozzle 
     22  ignition gas tube 
     23  fuel tube 
     25  oxygen channel 
     26  oxygen 
     27  gas turbine unit 
     28  compressor 
     29  gas turbine 
     30  combustion chamber 
     31  ignition device 
     32  ignition fuel supply 
     33  valve 
     34  ignition air storage 
     35  external ignition air supply 
     36 , 37  check valve 
     38  combustion air inlet 
     39  exhaust gas outlet 
     42  exit chamber 
     43 , 46  connecting channel 
   While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in its entirety.