Abstract: A compressor variable angle measurement system for guiding the positioning variable vanes supported on a penny of a compressor of a gas turbine engine. The system comprising a gauge assembly that is connectable to a computing device. the gauge assembly comprises a base plate and a clamp arm. The gauge assembly is configured to removably grip a variable vane between three vane contact portions of the baseplate and the vane contact portion of the clamp arm and on the leading edge vane engaging portion and the trailing edge vane engaging portion of the base plate, the stagger angle of the variable vane with respect to the radial setting pin being determined by the computing device from measurements made by an inertial measurement unit.

Abstract: An electrical power generation system including a micro-turbine alternator including a combustion chamber, at least one turbine driven by combustion gases from the combustion chamber, a first stage compressor, and a second stage compressor located aft of the first stage compressor. The first stage compressor and the second stage compressor being operably connected to the combustion chamber to provide a compressed airflow thereto. The micro-turbine alternator including one or more shafts connecting the at least one turbine to the first stage compressor and the second stage compressor such that rotation of the at least one turbine drives rotation of the first and second stage compressor. An electric generator is disposed along the one or more shafts such that electrical power is generated via rotation of the one or more shafts. The electric generator is disposed along the one or more shafts between the first and second stage compressors.

Abstract: A supercritical CO2 turbo-generator system includes multiple turbine generator units, a direct current bus, a plurality of active rectifiers, and a voltage controller. Each turbine generator unit includes a turbine with a supercritical CO2 input and a supercritical CO2 output, a generator with an electrical input and power output, a shaft connecting the turbine and generator, and a speed sensor for sensing shaft speed. The turbine generator units are connected in a cascading series with the input of a first turbine generator unit connected to a heated supercritical CO2 source and the input of each subsequent turbine generator unit is connected to the output of a prior turbine generator unit. The voltage controller monitors the speed sensor of the turbine generator units and varies the load on each generator to control shaft speed. Each active rectifier converts the power output of a generator to direct current, and the power from multiple active rectifiers is combined by the direct current bus.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustion system comprising a fuel metering unit; and an engine controller configured to, in response to a change of a throttle lever angle setting indicative of an acceleration event, increase fuel flow to the combustion system by the fuel metering unit, and to operate the first electric machine in a motor mode to increase the HP spool rotational speed and engine core mass flow.

Abstract: A bleed air cooling system for a gas turbine engine includes one or more bleed flowpaths operably connected to a bleed outlet to divert a bleed airflow from a gas turbine engine flowpath. Each bleed flowpath includes two or more bleed ports to divert a bleed airflow from a gas turbine engine flowpath, and a bleed duct in fluid communication with the bleed ports and configured to convey the bleed airflow from the two or more bleed ports to the bleed outlet. A valve is located at each bleed port of and is configured to move between an opened position and a closed position, and one or more sensors are located along the bleed flowpath to sense one or more conditions of the bleed air cooling system. The valve at a particular bleed port is moved to the opened position based on the sensed one or more conditions.

Abstract: A surge control system includes a rotor system with at least one compressor section and at least one turbine section operably coupled to a shaft. The surge control system also includes sensors configured to collect sensor data from the rotor system, an electric motor operably coupled to the rotor system, and a controller. The controller is operable to detect surge event from the sensor data, determine an amount of power to apply to the rotor system, and increase the amount of power provided to the rotor system to recover from the surge event.

Abstract: An apparatus for optimizing control parameters of a power plant is provided. The apparatus for optimizing control parameters of a power plant includes: a model generator configured to configure a forecast model including a process model and a control model, a model corrector configured to correct a first parameter of the process model through operation data of a real power plant, and a tuner configured to tune a second parameter, which is a parameter related to a time delay of the forecast model, so as to have a target load increase rate.

Abstract: A Raman scattered light acquisition device includes an emitting optical system configured to guide excitation light into a fluid, a scattered light window configured to define a part of a flow path of the fluid and through which Raman scattered light from the fluid irradiated with the excitation light passes, and a scattered light receiving device having a light receiving surface receiving Raman scattered light passed through the scattered light window. The scattered light window and the light receiving surface of the scattered light receiving device are disposed at a position in which they are separated from an optical axis in the fluid in a radial direction within a range in which an optical path of the excitation light in the fluid is present in an optical axis direction in which the optical axis in the fluid which is an optical axis of the excitation light in the fluid extends.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustion system comprising a fuel metering unit; and an engine controller configured to, in response to a change of a power lever angle setting indicative of a deceleration event, reduce fuel flow to the combustion system by the fuel metering unit, and to operate the first electric machine in a generator mode to reduce the HP spool rotational speed and engine core mass flow.

Abstract: A combustion device includes an ammonia supply unit supplying primary reduction ammonia as a nitrogen oxide reducing agent into a combustor and mixing secondary reduction ammonia with combustion exhaust gas discharged from the combustor to reduce nitrogen oxide contained in the combustion exhaust gas and a controller configured to control at least one of the amount of supply of the primary reduction ammonia and the amount of mixing of the secondary reduction ammonia with the combustion exhaust gas in accordance with concentrations of residual nitrogen oxide and residual ammonia contained in the combustion exhaust gas after being discharged from the combustor.

Abstract: A gas turbine engine includes a low-pressure spool, a high-pressure spool, and an electric motor. The low-pressure spool includes a low-pressure compressor in rotational communication with a low-pressure turbine and a fan via a first shaft. The high-pressure spool includes a high-pressure compressor in rotational communication with a high-pressure turbine via a second shaft. The electric motor is operably connected to the second shaft. The electric motor is configured to apply a rotational force to the second shaft.

Abstract: A carbonaceous feedstock gasification power generation facility, and a method for regulating a gas for drying gas this carbonaceous feedstock, are disclosed with which it is possible to expand the range of the types of carbonaceous feedstocks that can be used. High-temperature exhaust gas, low-temperature exhaust gas and extreme high-temperature exhaust gas are bled from the furnace respectively at a high-temperature bleed position, a low-temperature bleed position and an extreme high-temperature bleed position. When these exhaust gases are mixed, the flow volume of the extreme high-temperature exhaust gas supplied to at least one of the exhaust gases, that is, the high-temperature exhaust gas or the low-temperature exhaust gas, is adjusted such that the temperature of at least one of these exhaust gases, that is, the high-temperature exhaust gas or the low-temperature exhaust gas, reaches a prescribed temperature.

Abstract: A movable electrical generation system includes a generator operable to produce a supply of electrical energy, a prime mover operable to drive the generator, a first fuel, a second fuel different from the first fuel, a control system operable to deliver one of the first fuel and the second fuel to the prime mover and to control an electrical load applied to the generator based on one of a first fuel current protection limit and a second fuel current protection limit.

Abstract: A system includes a controller circuit configured to provide control inputs to at least one component of a subsea electrical system, a simulator circuit coupled to the controller circuit and configured to maintain a model of the subsea electrical system and apply the control inputs to the model concurrent with provision of the control inputs to the at least one component and a monitor circuit coupled to the simulator circuit and configured to identify a status of the subsea electrical system responsive to the model. The simulator circuit may be configured to modify the model responsive to feedback signals received from the subsea electrical system and the monitor circuit may be configured to identify the status of the subsea electrical system responsive to a modification of the model.

Abstract: Systems and methods for controlling a fluid-based system are disclosed. The systems and methods may include a model processor for generating a model output, the model processor including a set state module for setting dynamic states, the dynamic states input to an open loop model based on the model operating mode, where the open loop model generates current state derivatives, solver state errors, and synthesized parameters as a function of the dynamic states and a model input vector. A constraint on the current state derivatives and solver state errors is based on mathematical abstractions of physical laws that govern behavior of a component using a material temperature utility. The model processor may further include an estimate state module for determining an estimated state of the model based on at least one of a prior state, the current state derivatives, the solver state errors, and the synthesized parameters.

Abstract: A fault detection assembly for an aircraft system according to an example of the present disclosure includes, among other things, a transmitter that communicates an electrical input signal to a first portion of an electrical connector, the first portion moveable between a fully seated position and a fully unseated position relative to a second portion of the electrical connector to define a range of insertion depths, a receiver that senses an electrical output signal relating to the electrical input signal, and a comparison module that determines an insertion depth in the range of insertion depths based on a change in a resonant frequency of the electrical output signal with respect to the electrical input signal.

Abstract: A propulsion system for an unmanned underwater vehicle includes at least one fuel storage tank. A plurality of combustors is connected to the at least one fuel storage tank. Each of the combustors is connected to a turbine via a corresponding nozzle. An output shaft is connected to the turbine and configured to output rotational energy from the turbine.

Abstract: Systems and methods for controlling a fluid based engineering system are disclosed. The systems and methods may include a model processor for generating a model output, the model processor including a set state module for setting dynamic states of the model processor, the dynamic states input to an open loop model based on the model operating mode. The model processor may include an input object for processing model input and setting a model operating mode, the model operating mode being a starting mode if the model input is within a data range associated with a starting operation of the control device. The model processor may further include an estimate state module for determining an estimated state of the model based on a prior state model output and the current state model of the open loop model.

Abstract: A method of controlling and managing a process control system having a plurality of control loops includes implementing a plurality of control routines to control operation of the plurality of control loops, respectively, wherein the control routines may include at least one non-adaptive control routine. The method then collects operating condition data in connection with the operation of each control loop, and identifies a respective process model for each control loop from the respective operating condition data collected for each control loop. The identification of the respective process models may be automatic as a result of a detected process change or may be on-demand as a result of an injected parameter change. The process models are then analyzed to measure or determine the operation of the process control loops.

Abstract: In one embodiment, a system includes a gas turbine system, having: a turbine driven by combustion products produced by a turbine combustion system; and a separation unit positioned between turbine stages of the turbine, wherein the separation unit separates oxygen out of the combustion products. The separation unit may include an ion transport membrane.

Abstract: Systems and methods for controlling a gas turbine engine are provided. The system comprises an interface to a fuel flow metering valve for controlling a fuel flow to the engine in response to a fuel flow command and a controller connected to the interface and configured for outputting the fuel flow command to the fuel flow metering valve in accordance with a required fuel flow. The controller comprises a feedforward controller configured for receiving a requested engine speed, obtaining a steady-state fuel flow for the requested engine speed as a function of the requested engine speed, the steady-state fuel flow, and the relationship between fuel flow and gas generator speed, and determining the required fuel flow to obtain the requested engine speed and the relationship between fuel flow and gas generator speed.

Abstract: Systems and methods for controlling a fluid based system are disclosed. The systems and methods may include a model processor for generating a model output, the model processor including a set state module for setting dynamic states, the dynamic states input to an open loop model based on the model operating mode, where the open loop model generates current state derivatives, solver state errors, and synthesized parameters as a function of the dynamic states and a model input vector. A constraint on the state derivatives and solver state errors is based on a material temperature utility for determining a material temperature associated with a component of the cycle of the control system. The model processor may include an estimate state module for determining an estimated state of the model based on at least one of a prior state, the current state derivatives, the solver state errors, and the synthesized parameters.

Abstract: A method for controlling a turbine is proposed, which is characterized at any point in the control by a hidden state. The dynamic behavior of the turbine is modeled with a recurrent neural network comprising a recurrent hidden layer. In this case, the recurrent hidden layer is formed from vectors of neurons, which describe the hidden state of the turbine at the time points of the regulation, wherein two vectors are chronologically linked for each time point with a first connection bridging a time and second connection bridging at least two points in time. Short-term effects can be controlled by means of the first connections and long-term effects can be adjusted by means of the second connections. Secondly, emissions and also occurring dynamics in the turbine can be minimized. Furthermore, a regulating device and a turbine with such a regulating device are proposed.

Abstract: A turbine engine includes a compressor, and high and low pressure turbines. The configuration includes a mid-compression station which can be, in the case of a single compressor in the middle of that compressor, or at the exit of the first compressor in the case of two compressors. Also, there is an exit pressure station at the exit of the compression system. A first gas flow line is interposed between the mid-compression station of the compressor and the low pressure turbine, and a second gas flow line is interposed between the exit pressure station of the compression system and the high pressure turbine. A first valve is coupled to the first gas flow line and modulates a low pressure flow rate of coolant in the first gas flow line, and a second valve is coupled to the second gas flow line and modulates a high pressure flow rate of coolant in the second coolant flow line.

Abstract: A system configured to precisely control and/or modulate purge flow in a power plant system (e.g., a gas turbine) during operation is disclosed. In one embodiment, a system includes: at least one computing device adapted to control a purge flow in a gas turbine by performing actions comprising: obtaining operational data from the gas turbine; determining an inferred gas path pressure value for the gas turbine; determining an allowable purge flow for the gas turbine as a function of the operational data and the inferred gas path pressure value; and adjusting the purge flow based upon the allowable purge flow determination.

Abstract: The aim of the invention is to improve the efficiency of an axial-piston motor. To this end, the axial-piston motor comprises at least one compressor cylinder, at least one working cylinder and at least one pressure line guiding the compressed fuel from the compressor cylinder to the working cylinder. A working piston comprising a working rod is provided in the working cylinder, and a compressor piston comprising a compressor rod is provided in the compressor cylinder. The axial-piston motor is characterized in that it at least one of the two rods comprises transverse stiffeners.

Abstract: A turbine power generation system with enhanced stabilization of refractory carbides provided by hydrocarbon from high carbon activity gases is disclosed. The disclosure also includes a method of using high carbon activity gases to stabilize hot gas path components.

Abstract: A gas turbine engine is disclosed which is capable of being reconfigured for one operating mode to another. A display is provided that permits a pilot or other operator to select between engine modes. One aspect is the ability to provide variable cooling that can be controlled by various devices. The variable cooling features can be used with devices such as cooled turbine components like vanes and/or blades. Devices can be used to reconfigure the performance and/or operability of a gas turbine engine.

Abstract: An exemplary method is disclosed for operating a gas turbine power plant with exhaust gas recirculation, in which the exhaust gas recirculation is, for example, disengaged during starting and shutting down of the gas turbine, and in which the engaging or disengaging of the exhaust gas recirculation can be carried out in dependence upon an operating state of the gas turbine. An exemplary gas turbine power plant with exhaust gas recirculation is also disclosed which can include a control element, the closing speed of which is such that the control element can be closed within a time which is less than a time for exhaust gases to flow from the turbine through an HRSG.

Abstract: In a gas turbine engine that includes a compressor and a combustor, wherein the combustor includes a primary fuel injector within a fuel nozzle and a secondary fuel injector that is upstream of the fuel nozzle and configured to inject fuel into a flow annulus of the combustor, a method for detecting a flame holding condition about a fuel injector. The method may include the steps of: detecting an upstream pressure upstream of the secondary fuel injector; detecting a downstream pressure downstream of the secondary fuel injector; determining a measured pressure difference between the upstream pressure and the downstream pressure; and comparing the measured pressure difference to an expected pressure difference.

Abstract: A gas turbine engine is provided having a variety of forms and features. The gas turbine engine can include a compressor having movable vanes. In one form of operation the compressor can close down the vanes to a relatively low flow capacity position and the compressor can be operated at a higher speed, whereupon the vanes can be repositioned and the gas turbine engine operated at a different condition. The gas turbine engine can include a turbine having movable vanes. In one form of operation the turbine can change the vane positions to a relatively low torque position and the engine operated at a higher fuel flow condition, whereupon the vanes can be repositioned and the gas turbine engine operated at a different condition. The gas turbine engine can have a heater that adds heat to a flow stream, a motor that provides energy to a shaft, and an external load.

Abstract: A system includes an anti-icing heat recovery system, which includes a first heat exchanger, a second heat exchanger, and a variable speed fan. The first heat exchanger is configured to receive a working fluid from an exhaust section of a gas turbine engine and to transfer heat from the working fluid to a cooled intermediate heat transfer medium to generate a heated intermediate heat transfer medium. The second heat exchanger is configured to receive the heated intermediate heat transfer medium from the first heat exchanger and to transfer heat from the heated intermediate heat transfer medium to air entering the gas turbine engine. The variable speed fan is configured to urge the working fluid from the exhaust section of the gas turbine engine through the first heat exchanger.

Abstract: Systems and methods for supplying fuel to a gas turbine are described. A fuel may be received, and one or more parameters associated with the received fuel may be determined. Based at least in part upon the determined one or more parameters, a desired pressure for removing one or more liquids from the fuel utilizing a separator may be calculated. The operation of a pressure changing device may then be controlled in order to achieve the desired pressure. In certain embodiments, the operations of the method may be performed by a controller that includes one or more computers.

Abstract: An automated industrial system is provided that includes a sensor system configured to monitor multiple parameters. The automated industrial system also includes a controller. The controller is configured to determine if any of the multiple parameters has surpassed a respective constraint threshold of multiple constraint thresholds. If any of the parameters has surpassed a respective constraint threshold, the controller is configured to classify a parameter of the multiple parameters which has surpassed the respective constraint threshold by the highest degree as the most constrained parameter. The controller is also configured to calculate a minimum temperature load path based on the most constrained parameter, with the minimum temperature load path configured to transition the automated industrial system from a base load to a part load via a minimum temperature load path.

Abstract: Gas turbine firing temperature optimization based on a measured sulfur content of a fuel supply of the gas turbine system is provided. In one embodiment, a system includes a diagnostic system configured to determine a maximum firing temperature for a combustor of a gas turbine system. The diagnostic system may determine the maximum firing temperature based on a predetermined sulfur content to maximum firing temperature correlation and an actual sulfur content of a fuel supplied to the combustor. The diagnostic system may also be configured to provide an indicator for a change in an actual firing temperature in the combustor of the gas turbine system. The diagnostic system may provide the indicator in response to the determined maximum firing temperature differing from the actual firing temperature of the combustor of the gas turbine system.

Abstract: A method is provided for operating a gas turbine in a power station in which limits of the operating concept, which provide limits for optimization of the power station operation in respect of efficiency, service life consumption, emissions and power provision to the grid system, are adapted during operation. In particular, temperature limits and compressor inlet guide vane position limits are varied as a function of the optimization aims. A gas turbine power station is also provided for carrying out the method.

Abstract: The method for adjusting a natural gas temperature for a fuel supply line of a gas turbine engine includes measuring by infrared analysis the natural gas percentage content of methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), carbon dioxide (CO2), calculating the nitrogen (N2) percentage content as the complement to 100 of the measured percentage content of methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), carbon dioxide (CO2), calculating an index indicative of the natural gas energy content and adjusting the natural gas temperature on the basis of the index.

Abstract: A system includes a controller configured to control a semi-closed power cycle system. The controller is configured to receive at least one of a first signal indicative of an oxygen concentration within a first gas flow through a primary compressor, a second signal indicative of power output by the semi-closed power cycle system, a third signal indicative of a temperature of a second gas flow through a turbine, and a fourth signal indicative of a mass flow balance within the semi-closed power cycle system. The controller is also configured to adjust at least one of the first gas flow through the primary compressor, a fuel flow into a combustor, a fraction of the first gas flow extracted from the primary compressor, and an air flow through a feed compressor based on the at least one of the first signal, the second signal, the third signal, and the fourth signal.

Abstract: In one embodiment, a system includes at least one sensor configured to communicate a signal representative of a gas turbine operations. The system further includes a controller communicatively coupled to the sensor. The system additionally includes a stoichiometric model configured to receive one or more inputs representative of the gas turbine operations and a measured equivalence ratio, wherein the controller is configured to transform the signal into the one or more inputs and to use the stoichiometric model to derive an actuation signal based on a target equivalence ratio.

Abstract: One embodiment according to the present invention is a unique system for gas turbine engine control. Other embodiments include unique apparatuses, systems, devices, and methods relating to gas turbine engines. Further embodiments, forms, objects, features, advantages, aspects, and benefits of the present invention shall become apparent from the following description and drawings.

Abstract: A speed control system for an engine comprising at least one rotary load is provided. The speed control system may include a rotor speed controller configured to regulate speed in the rotary load based on a sensed rotor speed, exclusive of resonant mode speed oscillations, in closed loop feedback with a commanded rotor speed. To provide active damping of resonant mode speed oscillations, a resonance disturbance rejection controller may be configured to compensate a speed control signal by observing a component of the sensed rotor speed that is due to resonant mode oscillations. Based on the observed resonance component, the resonance disturbance rejection controller may compute an adjustment value for the speed control signal. In the particular case of gas turbine engines, the resonance disturbance rejection controller may effect active damping by compensation of a fuel flow request for a gas generator.

Abstract: A control apparatus for controlling a compressor driven by a driving unit generating driving power by a gas turbine and an electric motor includes: a temperature detection section for detecting an exhaust gas temperature of the gas turbine; and a control section for generating a motor torque instruction value for the electric motor based on the detected exhaust gas temperature. Such a control apparatus can realize a control so as not to distribute a load on the electric motor when the exhaust gas temperature of the gas turbine is low and a driving power is low. As a result, the operation efficiency can be enhanced.

Abstract: This invention relates generally to gas turbine engine thrust scheduling, and more particularly to systems and methods for smoothing thrust inputs to gas turbine engines. In one embodiment, a method for operating a gas turbine engine comprises, upon disengagement of an auto-throttle system, determining a first trim setting corresponding to a TLA setting, determining a second trim setting where the second trim setting reduces to zero during successive manual throttle lever movements, determining a third trim setting comprising a combination of the first trim setting and the second trim setting, and applying the third trim setting to the TLA setting to smoothly transition from auto-throttle to manual operation of the engine while maintaining engine thrust.

Abstract: Systems and methods for accelerating droop response in a combined cycle power plant are provided. According to one embodiment if the disclosure, a system may include a controller and a processor communicatively coupled to the controller. The processor may be configured to receive frequency variation data associated with a frequency variation of an electrical grid, determine, based at least in part on the frequency variation data, a target operational level of the combined cycle power plant and the droop response associated with the target operational level, calculate a variable compensation value, and apply the variable compensation value to the droop response until the target operational level is reached.

Abstract: A method is provided for operating a gas turbine in the event of load shedding and/or rapid shutdown. The method includes operating the gas turbine by the combustion of fuel in a combustion chamber of the gas turbine with the addition of combustion air via an air passage, and driving a load. Upon or directly after the load shedding or rapid shutdown, an additional gas volume is supplied to the combustion chamber via the air passage in order to slow the drop in pressure level in the combustion chamber.

Abstract: A method for controlling a turbine engine generator set is disclosed. The method comprises: sensing an operating parameter indicative of a load increase on the turbine engine generator set; operating the turbine engine generator set in a first mode when the sensed operating parameter is within a predetermined range; and operating the turbine engine generator set in a second mode when the sensed operating parameter is outside the predetermined range. The second mode provides a rate of adjustment of operation of the turbine engine generator set that is greater than a rate of adjustment during the first mode.

Abstract: A condition measurement apparatus is provided and includes a gas turbine engine combustor having an end cover, a liner defining a liner interior and a fuel nozzle communicative with the liner interior, the end cover being formed to separate a cold side thereof, which is a relatively low temperature environment, from a hot side thereof, which is a relatively high temperature environment in which the liner and the fuel nozzle are disposed, the combustor being formed to define a fuel flow path extending through piping disposed at the cold side of the end cover by which fuel is deliverable to the fuel nozzle, and a condition sensing device operably mounted on the piping.

Abstract: A method and system for controlling a two-shaft turbine engine, the two-shaft turbine engine including a gas producer having a compressor with adjustable inlet guide vanes. The method includes monitoring a rotational speed of the gas producer, maintaining an inlet guide vane angle constant when a rotational speed of the gas producer is below a threshold value, and adjusting an inlet guide vane angle of the compressor at a predetermined rate when the rotational speed of the gas producer is above the threshold value.

Abstract: A system includes a gas turbine system model configured to model a turbine system operational behavior of a gas turbine system, and a shaft contribution model (SCM) including a bottoming cycle performance (BCP) model configured to model a bottoming cycle behavior of a bottoming cycle system. The gas turbine system model is configured to receive a SCM output from the SCM and to use the SCM output to control an actuator. The actuator is operatively coupled to the gas turbine system.

Abstract: A method of controlling a power plant that comprises a working fluid and a recirculation loop, wherein the power plant includes a combustor operably connected to a turbine, the method including the steps of: recirculating at least a portion of the working fluid through the recirculation loop; controlling the power plant such that the combustor at least periodically operates at a preferred stoichiometric ratio; and extracting the working fluid from at least one of a first extraction point and a second extraction point positioned on the recirculation loop during the periods when the combustor operates at the preferred stoichiometric ratio.