System and method for modular control of a multi-fuel low emissions turbogenerator

Abstract

A system and method for modular control of a multi-fuel turbogenerator include separate controllers for controlling fuel supplied to the combustor and power output from the generator. The power controller generates a fuel command based on the required turbine exhaust temperature, where the fuel command is independent of the particular fuel being used. Fuels may include natural gas, diesel, propane, waste gas, or gasoline, for example. The power controller communicates the fuel command and the airflow or calculated air/fuel ratio to the fuel controller which selects an appropriate mode of operation for the injectors. Injector operating modes include one or more pilot modes where fuel is not mixed with air prior to combustion, and one or more premix modes where fuel is highly mixed with air prior to combustion. The fuel controller implements closed-loop feedback control of a fuel metering device and controls the fuel injectors in the appropriate operating mode based on the fuel command, the energy content of the fuel being used, and the air/fuel ratio.

What is claimed is:  
     
         1 . A method for controlling a turbogenerator, comprising: 
 in a first controller, determining an air/fuel ratio based on an air flow and fuel flow;    communicating the air/fuel ratio to a second controller; and    in the second controller, selecting a fuel injector mode of operation based upon the air/fuel ratio to maintain flame stability.    
     
     
         2 . The method of  claim 1  wherein determining an air/fuel ratio includes determining current air flow of the turbogenerator in the first controller.  
     
     
         3 . The method of  claim 2  wherein determining current air flow comprises determining current air flow based on ambient air temperature, ambient air pressure, and turbine speed.  
     
     
         4 . The method of  claim 3  wherein determining current air flow comprises referencing a lookup table based on the ambient air temperature, the ambient air pressure, and the turbine speed.  
     
     
         5 . The method of  claim 2  wherein determining current air flow comprises measuring actual air flow through the turbogenerator.  
     
     
         6 . The method of  claim 1  wherein determining fuel flow comprises determining fuel demand to maintain a desired turbine exhaust temperature.  
     
     
         7 . The method of  claim 1  wherein determining fuel flow comprises determining a minimum fuel demand based on a computed air flow, a maximum air/fuel ratio to sustain combustion, and energy content of a particular fuel being used.  
     
     
         8 . The method of  claim 7  wherein the maximum air/fuel ratio and the energy content of the particular fuel being used are communicated from the second controller to the first controller.  
     
     
         9 . The method of  claim 1  wherein determining fuel flow comprises estimating fuel flow into the turbogenerator.  
     
     
         10 . The method of  claim 1  wherein determining fuel flow comprises measuring fuel flow into the turbogenerator.  
     
     
         11 . The method of  claim 1  wherein determining fuel flow comprises determining fuel temperature and fuel pressure across a proportioning valve.  
     
     
         12 . The method of  claim 1  wherein determining fuel flow comprises measuring fuel flow into the turbogenerator using a fuel flow meter.  
     
     
         13 . The method of  claim 1  wherein determining an air/fuel ratio comprises calculating the air/fuel ratio based on a fuel command from the first controller.  
     
     
         14 . The method of  claim 1  wherein determining an air/fuel ratio comprises calculating the air/fuel ratio in the first controller using a measured fuel flow into the turbogenerator as determined by the second controller.  
     
     
         15 . The method of  claim 1  wherein determining an air/fuel ratio comprises calculating the air/fuel ratio using a fuel command in the second controller.  
     
     
         16 . The method of  claim 1  further comprising: 
 selecting an operating mode for at least one injector of the turbogenerator based at least in part on the determined air/fuel ratio, wherein the step of controlling the fuel supplied to the turbogenerator includes controlling fuel supplied to the injector based on the injector operating mode.  
 
     
     
         17 . The method of  claim 16  wherein selecting an operating mode comprises selecting a pilot mode or a premix mode.  
     
     
         18 . The method of  claim 1  further comprising: 
 selecting an operating mode for a plurality of injectors of the turbogenerator based at least in part on the determined air/fuel ratio, wherein operating modes include premix and pilot modes.  
 
     
     
         19 . The method of  claim 18  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting the premix mode and the step of controlling the fuel supplied to the turbogenerator includes energizing at least one of the premix injectors.  
     
     
         20 . The method of  claim 18  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting the premix mode and the step of controlling the fuel supplied to the turbogenerator includes energizing any combination of the premix injectors.  
     
     
         21 . The method of  claim 18  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting a premix mode and the step of controlling the fuel supplied to the turbogenerator includes sequentially energizing any combination of the premix injectors.  
     
     
         22 . The method of  claim 21  wherein sequentially energizing any combination of the premix injectors comprises sequentially energizing the premix injectors to promote swirl within a combustor.  
     
     
         23 . The method of  claim 18  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode and the step of controlling the fuel supplied to the turbogenerator includes energizing at least one of the pilot injectors.  
     
     
         24 . The method of  claim 18  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode and the step of controlling the fuel supplied to the turbogenerator includes energizing any combination of the pilot injectors.  
     
     
         25 . The method of  claim 18  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode and the step of controlling the fuel supplied to the turbogenerator includes sequentially energizing any combination of the pilot injectors.  
     
     
         26 . The method of  claim 25  wherein sequentially energizing any combination of the pilot injectors comprises sequentially energizing the pilot injectors to promote swirl within a combustor.  
     
     
         27 . The method of  claim 18  wherein selecting an operating mode comprises selecting a pilot mode and wherein the step of controlling the fuel supplied to the turbogenerator includes energizing all of the injectors.  
     
     
         28 . The method of  claim 1  further comprising: 
 transitioning between selected operating modes based on a change in air/fuel ratio of the turbogenerator; and  
 energizing an ignitor of the turbogenerator while transitioning.  
 
     
     
         29 . The method of  claim 1  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator; and  
 increasing the quantity of fuel supplied to injectors of the turbogenerator while transitioning to improve combustion stability.  
 
     
     
         30 . The method of  claim 29  wherein increasing the quantity of fuel while transitioning comprises modifying a desired operating temperature of the turbogenerator.  
     
     
         31 . The method of  claim 30  wherein modifying a desired operating temperature comprises raising desired turbine exhaust temperature while transitioning between operating modes.  
     
     
         32 . The method of  claim 29  wherein transitioning between operating modes includes transitioning between a premix mode in which fuel is well mixed with air prior to delivery into a combustor of the turbogenerator and at least one pilot mode in which fuel is not substantially mixed with air prior to delivery into a combustor.  
     
     
         33 . The method of  claim 32  wherein the pilot mode comprises a plurality of pilot modes each corresponding to operation of a varying number of injectors.  
     
     
         34 . The method of  claim 1  further comprising transitioning between a first premix operating mode and a second premix operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         35 . The method of  claim 34  wherein transitioning between first and second premix operating modes includes transitioning from operation of a first premix injector to an additional plurality of premix injectors.  
     
     
         36 . The method of  claim 35  wherein the plurality of premix injectors comprises three premix injectors.  
     
     
         37 . The method of  claim 1  further comprising transitioning between a first pilot operating mode and a second pilot operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         38 . The method of  claim 37  wherein transitioning between first and second pilot operating modes includes transitioning from operation of a first pilot injector to an additional plurality of pilot injectors.  
     
     
         39 . The method of  claim 38  wherein the plurality of pilot injectors comprises three pilot injectors.  
     
     
         40 . The method of  claim 1  further comprising transitioning between a first pilot operating mode and a first premix operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         41 . The method of  claim 37  wherein transitioning between the first and second pilot modes comprises energizing injectors in a sequence which generates a desired swirl within a combustor of the turbogenerator.  
     
     
         42 . The method of  claim 1  wherein communicating the desired air/fuel ratio comprises communicating the desired air/fuel ratio via external communications.  
     
     
         43 . The method of  claim 1  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator;  
 communicating a transitioning signal to the first controller; and  
 increasing target turbine exhaust temperature to improve combustion stability during transitioning.  
 
     
     
         44 . The method of  claim 1  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator;  
 communicating a transitioning signal from the second controller to the first controller; and  
 energizing an ignitor while transitioning.  
 
     
     
         45 . A method for controlling a turbogenerator, comprising: 
 in a first controller, determining a desired fuel command in units independent of a specific fuel based on a turbogenerator operating parameter;    communicating the desired fuel command to a second controller;    in the second controller, converting the independent fuel command to a fuel command specific to the fuel currently utilized in the turbogenerator; and    controlling the delivery of fuel to the turbogenerator, including communicating fuel command limits from the second controller back to the first controller.    
     
     
         46 . The method of  claim 45  wherein the turbogenerator operating parameter is turbine exhaust temperature.  
     
     
         47 . The method of  claim 46  wherein communicating the desired fuel command comprises communicating the desired fuel command from the first controller to the second controller via an external communications bus.  
     
     
         48 . The method of  claim 46  further comprising: 
 converting the desired fuel command in the second controller to a fuel quantity based on energy content of the fuel being combusted.  
 
     
     
         49 . The method of  claim 45  wherein the desired fuel command is in units of energy per unit time.  
     
     
         50 . The method of  claim 45  further comprising: 
 determining a fuel command upper limit in the second controller based on a maximum amount of fuel which can be delivered to the turbogenerator and energy content of the fuel.  
 
     
     
         51 . The method of  claim 45  further comprising: 
 determining a fuel command lower limit in the second controller based on a maximum air/fuel ratio for combustion and current airflow through the turbogenerator.  
 
     
     
         52 . The method of  claim 51  wherein the fuel command lower limit is determined by dividing the maximum air/fuel ratio by the current airflow and inverting the result.  
     
     
         53 . The method of  claim 45  wherein the desired fuel command is determined to maintain a substantially constant turbine exhaust temperature.  
     
     
         54 . The method of  claim 53  wherein determining the desired fuel command comprises: 
 measuring turbine exhaust temperature;  
 comparing turbine exhaust temperature to a desired turbine exhaust temperature to generate an error signal; and  
 determining the desired fuel command based on the error signal.  
 
     
     
         55 . The method of  claim 45  wherein controlling the delivery of fuel comprises controlling a fuel metering device.  
     
     
         56 . The method of  claim 55  wherein controlling the fuel metering device comprises: 
 determining a desired fuel flow command based on the desired fuel command and energy content of the fuel;  
 determining actual fuel flow;  
 comparing measured fuel flow to the desired fuel flow command to generate an error signal; and  
 controlling the fuel metering device to reduce the error signal.  
 
     
     
         57 . The method of  claim 56  wherein determining actual fuel flow includes estimating actual fuel flow.  
     
     
         58 . The method of  claim 56  wherein determining actual fuel flow includes measuring actual fuel flow using a flow meter.  
     
     
         59 . The method of  claim 56  wherein determining actual fuel flow includes calculating actual fuel flow based on fuel temperature and pressure across a proportioning valve.  
     
     
         60 . A method for controlling a turbogenerator, comprising: 
 in a first controller, determining current airflow of the turbogenerator and a desired energy flow;    communicating the desired energy flow and the current air flow to a second controller; and    in the second controller, calculating an air/fuel ratio and selecting a fuel injector mode of operation based upon the air/fuel ratio to maintain flame stability.    
     
     
         61 . The method of  claim 60  wherein the desired energy flow is determined in units independent of the particular fuel being combusted.  
     
     
         62 . The method of  claim 60  wherein determining actual fuel flow includes calculating actual fuel flow based on fuel temperature and pressure across a proportioning valve.  
     
     
         63 . The method of  claim 60  wherein selecting a fuel injector mode comprises selecting a pilot mode or a premix mode.  
     
     
         64 . The method of  claim 60  wherein selecting a fuel injector mode comprises selecting one of a plurality of pilot modes.  
     
     
         65 . The method of  claim 64  wherein each of the plurality of pilot modes corresponds to activation of a varying number of pilot injectors.  
     
     
         66 . The method of  claim 64  wherein the plurality of pilot modes includes a first pilot mode which activates one pilot injector and a second pilot mode which activates at least one additional pilot injector.  
     
     
         67 . The method of  claim 66  wherein the second pilot mode activates all of the pilot injectors.  
     
     
         68 . The method of  claim 60  wherein selecting a fuel injector mode comprises transitioning from a pilot mode to a premix mode.  
     
     
         69 . The method of  claim 60  further comprising energizing an ignitor to improve combustion stability during transitioning.  
     
     
         70 . The method of  claim 60  wherein selecting a fuel injector mode includes sequentially transitioning from a first pilot mode to a second pilot mode and then to a first premix mode.  
     
     
         71 . The method of  claim 70  wherein the first pilot mode supplies fuel to one pilot injector, the second pilot mode supplies fuel to two additional pilot injectors, and the first premix mode supplies fuel to three premix injectors.  
     
     
         72 . The method of  claim 71  wherein transitioning from the first pilot mode to the second pilot mode comprises energization of a second pilot injector adjacent the first pilot injector followed by energization of a third pilot injector adjacent the second pilot injector to facilitate ignition of fuel from the second and third pilot injectors by the first and second pilot injectors, respectively.  
     
     
         73 . The method of  claim 70  wherein transitioning from the second pilot mode to the first premix mode comprises energizing a plurality of premix injectors followed by sequentially de-energizing the pilot injectors.  
     
     
         74 . The method of  claim 70  wherein transitioning from the second pilot mode to the first premix mode comprises de-energizing a first pilot injector, energizing a plurality of premix injectors, and then sequentially de-energizing any remaining pilot injectors.  
     
     
         75 . The method of  claim 70  wherein transitioning from the second pilot mode to the first premix mode comprises sequentially de-energizing first and second pilot injectors, energizing a plurality of premix injectors, and then sequentially de-energizing any remaining pilot injectors.  
     
     
         76 . The method of  claim 60  wherein selecting a fuel injector mode includes transitioning from a premix mode to a pilot mode.  
     
     
         77 . The method of  claim 76  wherein the pilot mode comprises a plurality of pilot modes, the method further comprising transitioning from a first pilot mode to a second pilot mode.  
     
     
         78 . The method of  claim 60  wherein selecting a fuel injector mode includes transitioning from a premix mode with a plurality of premix injectors energized to a pilot mode with at least one pilot injector energized.  
     
     
         79 . The method of  claim 78  wherein the premix injectors and the pilot injectors are the same injectors operated in a premix mode and pilot mode, respectively.  
     
     
         80 . The method of  claim 78  wherein the plurality of premix injectors includes three premix injectors and the at least one pilot injector includes three pilot injectors.  
     
     
         81 . The method of  claim 80  wherein transitioning from a premix mode to a pilot mode comprises energizing at least one pilot injector prior to de-energizing the premix injectors.  
     
     
         82 . The method of  claim 80  wherein transitioning from a premix mode to a pilot mode comprises energizing a first pilot injector, de-energizing all premix injectors, then sequentially energizing any remaining pilot injectors.  
     
     
         83 . The method of  claim 80  wherein transitioning from a premix mode to a pilot mode comprises energizing a plurality of pilot injectors prior to de-energizing any premix injectors.  
     
     
         84 . The method of  claim 80  wherein transitioning from a premix mode to a pilot mode comprises energizing all pilot injectors prior to de-energizing any premix injectors.  
     
     
         85 . The method of  claim 60  wherein selecting a fuel injector mode includes transitioning from a first fuel injector mode to a second fuel injector mode based on a first value of an operating parameter of the turbogenerator and transitioning from the second fuel injector mode to the first fuel injector mode based on a second value of the operating parameter.  
     
     
         86 . The method of  claim 85  wherein the operating parameter is the air/fuel ratio.  
     
     
         87 . The method of  claim 60  wherein selecting a fuel injector mode includes transitioning from a first pilot mode to a second pilot mode based on a first value for the air/fuel ratio and transitioning from the second pilot mode to the first pilot mode based on a second value for the air/fuel ratio.  
     
     
         88 . The method of  claim 60  wherein selecting a fuel injector mode includes transitioning from a pilot mode to a premix mode based on a first value of the air/fuel ratio and transitioning from the premix mode to the pilot mode based on a second value of the air/fuel ratio.  
     
     
         89 . A system for controlling a turbogenerator, the system comprising: 
 a first controller for determining an air/fuel ratio based on an air flow and fuel demand;    a communications bus;    a second controller in communication with the first controller via the communications bus, the second controller selecting a fuel injector mode of operation based upon the air/fuel ratio to maintain low emissions combustion and flame stability.    
     
     
         90 . The system of  claim 89  wherein the first controller determines current air flow of the turbogenerator to determine the air/fuel ratio.  
     
     
         91 . The system of  claim 89  wherein the first controller determines current air flow based on ambient air temperature, ambient air pressure, and turbine speed.  
     
     
         92 . The system of  claim 89  wherein the second controller determines the fuel demand and communicates the fuel demand to the first controller via the communications bus.  
     
     
         93 . The system of  claim 89  wherein the second controller determines the fuel demand based on a maximum air/fuel ratio to sustain combustion and energy content of the fuel being used.  
     
     
         94 . The system of  claim 93  wherein the second controller communicates the maximum air/fuel ratio and the energy content of the fuel being used to the first controller.  
     
     
         95 . The system of  claim 89  wherein the communications bus is an external communications bus.  
     
     
         96 . The system of  claim 89  wherein the second controller estimates fuel flow into the turbogenerator.  
     
     
         97 . The system of  claim 89  further comprising: 
 a fuel metering device controlled by the second controller for controlling quantity of fuel delivered to at least one injector.  
 
     
     
         98 . The system of  claim 97  wherein the fuel metering device comprises a proportioning valve.  
     
     
         99 . The system of  claim 97  further comprising: 
 an upstream pressure sensor for sensing pressure of the fuel between a fuel source and the fuel metering device; and  
 a downstream pressure sensor for sensing pressure of the fuel between the fuel metering device and the injector.  
 
     
     
         100 . The system of  claim 97  wherein the fuel metering device comprises a fuel flow meter.  
     
     
         101 . The system of  claim 89  further comprising a plurality of injectors each being operable in a pilot mode and a premix mode, the injectors being controlled by the second controller.  
     
     
         102 . The system of  claim 89  wherein the second controller selects an operating mode for at least one injector based at least in part on the determined air/fuel ratio and controls fuel supplied to the injector based on the injector operating mode.  
     
     
         103 . A method for controlling a turbogenerator, comprising: 
 determining an air/fuel ratio based on power output of the turbogenerator; and    selecting an operating mode for at least one fuel injector based upon the air/fuel ratio to maintain flame stability.    
     
     
         104 . The method of  claim 103  further comprising determining power output of the turbogenerator based on measured power.  
     
     
         105 . The method of  claim 103  further comprising determining power output of the turbogenerator based on at least measured voltage.  
     
     
         106 . The method of  claim 103  further comprising determining power output of the turbogenerator based on at least measured current.  
     
     
         107 . The method of  claim 103  further comprising determining the air/fuel ratio by referencing a look-up table based on the turbogenerator output power.  
     
     
         108 . The method of  claim 103  further comprising determining a fuel flow based on the air/fuel ratio.  
     
     
         109 . The method of  claim 108  wherein determining a fuel flow comprises determining fuel demand to maintain a desired turbine exhaust temperature.  
     
     
         110 . The method of  claim 108  wherein determining fuel flow comprises determining a minimum fuel demand based on a computed air flow, a maximum air/fuel ratio to sustain combustion, and energy content of a particular fuel being used.  
     
     
         111 . The method of  claim 110  wherein the maximum air/fuel ratio and the energy content of the particular fuel being used are communicated from a second controller to a first controller, the first controller determining the air/fuel ratio based on the power output of the turbogenerator.  
     
     
         112 . The method of  claim 108  wherein determining fuel flow comprises estimating fuel flow into the turbogenerator.  
     
     
         113 . The method of  claim 108  wherein determining fuel flow comprises measuring fuel flow into the turbogenerator.  
     
     
         114 . The method of  claim 108  wherein determining fuel flow comprises determining fuel temperature and fuel pressure across a proportioning valve.  
     
     
         115 . The method of  claim 108  wherein determining fuel flow comprises measuring fuel flow into the turbogenerator using a fuel flow meter.  
     
     
         116 . The method of  claim 108  wherein determining fuel flow comprises determining current airflow through the turbogenerator.  
     
     
         117 . The method of  claim 103  further comprising: 
 selecting an operating mode for at least one injector of the turbogenerator based at least in part on the determined air/fuel ratio; and  
 controlling fuel supplied to the injector based on the injector operating mode.  
 
     
     
         118 . The method of  claim 117  wherein selecting an operating mode comprises selecting an operating mode based on the air/fuel ratio.  
     
     
         119 . The method of  claim 117  wherein selecting a operating mode comprises selecting an operating mode based on the output power of the turbogenerator.  
     
     
         120 . The method of  claim 117  wherein selecting an operating mode comprises selecting a pilot mode or a premix mode.  
     
     
         121 . The method of  claim 103  further comprising: 
 selecting an operating mode for a plurality of injectors of the turbogenerator based at least in part on the determined air/fuel ratio, wherein operating modes include premix and pilot modes.  
 
     
     
         122 . The method of  claim 121  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting the premix mode, the method further comprising controlling fuel supplied to the turbogenerator by energizing at least one of the premix injectors.  
     
     
         123 . The method of  claim 121  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting the premix mode, the method further comprising controlling fuel supplied to the turbogenerator by energizing any combination of the premix injectors.  
     
     
         124 . The method of  claim 121  wherein the plurality of injectors includes premix injectors and wherein selecting an operating mode comprises selecting a premix mode, the method further comprising controlling fuel supplied to the turbogenerator by sequentially energizing any combination of the premix injectors.  
     
     
         125 . The method of  claim 124  wherein sequentially energizing any combination of the premix injectors comprises sequentially energizing the premix injectors to promote swirl within a combustor.  
     
     
         126 . The method of  claim 121  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode, the method further comprising controlling fuel supplied to the turbogenerator by energizing at least one of the pilot injectors.  
     
     
         127 . The method of  claim 121  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode, the method further comprising controlling fuel supplied to the turbogenerator by energizing any combination of the pilot injectors.  
     
     
         128 . The method of  claim 121  wherein the plurality of injectors includes pilot injectors and wherein selecting an operating mode comprises selecting a pilot mode, the method further comprising controlling fuel supplied to the turbogenerator by sequentially energizing any combination of the pilot injectors.  
     
     
         129 . The method of  claim 128  wherein sequentially energizing any combination of the pilot injectors comprises sequentially energizing the pilot injectors to promote swirl within a combustor.  
     
     
         130 . The method of  claim 121  wherein selecting an operating mode comprises selecting a pilot mode, the method further comprising controlling the fuel supplied to the turbogenerator by energizing all of the injectors.  
     
     
         131 . The method of  claim 103  further comprising: 
 transitioning between injector operating modes based on a change in the determined air/fuel ratio of the turbogenerator; and  
 energizing an ignitor of the turbogenerator while transitioning.  
 
     
     
         132 . The method of  claim 103  further comprising: 
 transitioning between injector operating modes based on a change in output power of the turbogenerator.  
 
     
     
         133 . The method of  claim 103  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator; and  
 increasing a quantity of fuel supplied to injectors of the turbogenerator while transitioning to improve combustion stability.  
 
     
     
         134 . The method of  claim 133  wherein increasing the quantity of fuel while transitioning comprises modifying a desired operating temperature of the turbogenerator.  
     
     
         135 . The method of  claim 134  wherein modifying a desired operating temperature comprises raising desired turbine exhaust temperature while transitioning between operating modes.  
     
     
         136 . The method of  claim 133  wherein transitioning between operating modes includes transitioning between a premix mode in which fuel is well mixed with air prior to delivery into a combustor of the turbogenerator and at least one pilot mode in which fuel is not substantially mixed with air prior to delivery into a combustor.  
     
     
         137 . The method of  claim 132  wherein the pilot mode comprises a plurality of pilot modes each corresponding to operation of a varying number of injectors.  
     
     
         138 . The method of  claim 103  further comprising transitioning between a first premix operating mode and a second premix operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         139 . The method of  claim 138  wherein transitioning between first and second premix operating modes includes transitioning from operation of a first premix injector to an additional plurality of premix injectors.  
     
     
         140 . The method of  claim 139  wherein the plurality of premix injectors comprises three premix injectors.  
     
     
         141 . The method of  claim 103  further comprising transitioning between a first pilot operating mode and a second pilot operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         142 . The method of  claim 141  wherein transitioning between first and second pilot operating modes includes transitioning from operation of a first pilot injector to an additional plurality of pilot injectors.  
     
     
         143 . The method of  claim 142  wherein the plurality of pilot injectors comprises three pilot injectors.  
     
     
         144 . The method of  claim 103  further comprising transitioning between a first pilot operating mode and a first premix operating mode based on a change in determined air/fuel ratio of the turbogenerator.  
     
     
         145 . The method of  claim 141  wherein transitioning between the first and second pilot modes comprises energizing injectors in a sequence which generates a desired swirl within a combustor of the turbogenerator.  
     
     
         146 . The method of  claim 103  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator; and  
 increasing target turbine exhaust temperature to improve combustion stability during transitioning.  
 
     
     
         147 . The method of  claim 103  further comprising: 
 transitioning between operating modes based on a change in determined air/fuel ratio of the turbogenerator; and  
 energizing an ignitor while transitioning.  
 
     
     
         148 . A method for controlling a turbogenerator, the method comprising: 
 determining an air/fuel ratio for operation of the turbogenerator based on at least one operating parameter of the turbogenerator and physical characteristics of a fuel selected from a plurality of fuels which may be combusted within the turbogenerator; and    selecting an operating mode for at least one fuel injector of the turbogenerator based at least in part on the air/fuel ratio.    
     
     
         149 . The method of  claim 148  wherein determining an air/fuel ratio comprises determining an air/fuel ratio based on power output of the turbogenerator.  
     
     
         150 . The method of  claim 148  wherein determining an air/fuel ratio comprises calculating at least one fuel index based on the physical characteristics of the selected fuel.  
     
     
         151 . The method of  claim 148  further comprising: 
 determining an amount of fuel required to obtain the determined air/fuel ratio based on the selected operating mode; and  
 controlling a fuel metering device to deliver the required fuel to the turbogenerator.  
 
     
     
         152 . The method of  claim 151  wherein controlling a fuel metering device comprises controlling a fuel metering device based on the physical characteristics of the selected fuel.  
     
     
         153 . The method of  claim 152  wherein the fuel metering device is a proportioning valve.