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The method also includes increasing the first fuel amount to a third amount in response to an amplitude that is above a threshold value. The method further includes decreasing the first fuel amount from the third amount to a fourth amount. The fourth amount is about 0. Turbine engine may have, among other systems, a compressor system 10 , a combustor system 20 , a turbine system 70 , and an exhaust system In general, compressor system 10 compresses incoming air to a high pressure, combustor system 20 mixes the compressed air with a fuel and burns the mixture to produces high-pressure, high-velocity gas, and turbine system 70 extracts energy from the high-pressure, high-velocity gas flowing from the combustor system It should be emphasized that, in this discussion, only those aspects of turbine engine useful to illustrate the combustion control process will be discussed.
Compressor system 10 may include any device capable of compressing air. This compressed air may be directed to an inlet port of combustor system Combustor system 20 may include a plurality of fuel injectors 30 configured to mix the compressed air with a fuel and deliver the mixture to one or more combustors 50 of combustor system The fuel delivered to combustor 50 may include any liquid or gaseous fuel, such as diesel or natural gas.
The fuel delivered to combustor 50 may undergo combustion to form a high pressure mixture of combustion byproducts. The high temperature and high pressure mixture from combustor 50 may be directed to turbine system Energy may be extracted from these hot pressurized gases in turbine system For instance, the hot combustion gases may rotate blades connected to a shaft of the turbine, and thereby produce power.
The combustion gases may then exit turbine system 70 and optionally flow through exhaust after treatment systems not shown before being discharged to the atmosphere through exhaust system Fuel injector 30 may deliver fuel and air to combustor 50 for combustion. Combustion of fuel in combustor 50 may produce byproducts such as NO x , carbon monoxide CO , carbon dioxide CO 2 , and un-burnt hydrocarbons.
Government regulations may limit, among others, the amount of NO x that may be discharged through exhaust system Formation of NO x in combustor 50 may result from a reaction between oxygen and nitrogen at high temperatures.
Active Flow and Combustion Control
NO x formation may be reduced by reducing the temperature of the flame during combustion. Flame temperature may be reduced by reducing the concentration of fuel in the fuel and air mixture delivered to combustor However, when the fuel concentration is too low, the combustion process may become unstable. Instability in the combustion process may lead to oscillations in the combustion rate that may generate pressure pulses in combustor The combustion process in combustor 50 may be made stable by increasing the flame temperature in combustor Therefore, for low NO x emission, a lean fuel-air mixture that reduces flame temperature may be desired, while for stable combustion a higher fuel concentration may be desired.
Some embodiments of fuel injectors include multiple flow paths that deliver different concentrations of fuel and air to combustor These multiple flow paths may include a main flow path 35 and a pilot flow path The concentration of fuel in the main fuel stream may be low enough to achieve target NO x emission without causing unstable combustion.
The main fuel may burn in combustor 50 to create premixed flames Premixed flames 38 are the flames that are created when fuel and air are first mixed in fuel injector 30 and then burned in combustor The pilot fuel stream may burn in combustor 50 to create a diffusion flame Diffusion flames 48 are flames that are created when fuel and air mix and burn at the same time. Diffusion flames 48 may have a higher temperature than premixed flames 38 and may serve as a localized hot flame to stabilize the combustion process and prevent lean blowout.
Active Flow And Combustion Control 2014 Hardcover 2015 Ed.
In some embodiments, during normal operation, a majority of the fuel delivered to combustor 50 may be delivered through main flow path 35 and a small percentage may be delivered through pilot flow path A high proportion of the main fuel supply may enable the turbine engine to operate in a low NO x emitting mode during normal operation.
At some operating conditions of turbine engine load, temperature, etc. Once these pressure pulses occur, they may continue until variables that affect the combustion process are changed, to shift the operation of the turbine engine away from the unstable zone. In some embodiments of turbine engine , an unstable operating condition may be shifted by increasing the amount of pilot fuel delivered to combustor As described earlier, the pilot fuel creates a diffusion flame 48 at a temperature that stabilizes the combustion process.
Fuel injector 30 may have a generally tubular configuration with an inner and an outer tube arranged concentrically about a longitudinal axis The outer tube of fuel injector 30 may comprise a premix barrel 32 and the inner tube may comprise a pilot Premix barrel may be coupled to combustor 50 one end and to an injector housing 30 a at an opposite end. An annular space between premix barrel 32 and pilot 40 may include the main flow path 35 that delivers the main fuel stream to combustor Housing 30 a may include fuel lines and fuel galleries not shown that deliver fuel to fuel injector Compressed air from compressor system 10 may be directed into fuel injector 30 through an air swirler Air swirler 34 may include a plurality of curved or straight blades attached to fuel injector 30 to swirl the incoming compressed air.
Fuel nozzles 36 coupled to housing 30 a may inject fuel into the swirled air stream. Swirling the compressed air may help create a well mixed fuel-air mixture that comprises the main fuel supply. In embodiments of fuel injectors configured to deliver gaseous fuels or both liquid and gaseous fuels, fuel injector 30 may also include gas ports not shown to deliver the gaseous fuel to combustor Pilot 40 may be disposed radially inwards of premix barrel In some embodiments, pilot 40 and premix barrel 32 may be aligned both along longitudinal axis Pilot 40 may include components configured to deliver fuel and compressed air in pilot Pilot 40 may also include the pilot flow path Pilot flow path 45 may include components such as, ducts and nozzles configured to inject fuel and compressed air into combustor In embodiments of fuel injector 30 configured to deliver gaseous fuel or both liquid and gaseous fuel, pilot flow path 45 may include components configured to inject a stream of pressurized liquid and gaseous fuel into combustor The pressurized stream of fuel and air delivered to combustor 50 through pilot flow path 45 may comprise the pilot fuel stream.
In the preceding discussion, fuel injector 30 has been described mainly with reference to main flow path 35 and pilot flow path 45 which deliver the main flow stream and the pilot fuel stream, respectively, to combustor In the configuration of fuel injector 30 described herein, the main flow path 35 may be located circumferentially around pilot flow path In this configuration, the main fuel may be directed to combustor 50 circumferentially around the pilot fuel, and the premixed flame 38 may be formed around diffusion flame It should be emphasized that, although the disclosed combustion control process is illustrated using a specific configuration of fuel injector 30 , the combustion control process of the current disclosure will be applicable to any turbine engine where a pilot fuel supply and a main fuel supply are directed to combustor As described earlier, when combustion in combustor 50 becomes unstable, pressure or acoustic pulses may be generated in combustor These pressure pulses may range in frequency from a few hertz to a few thousand hertz.
A combustion control system may monitor the pressure pulses in combustor 50 and adjust the fuel flow into the combustor to prevent a pressure pulse at a frequency close to a natural frequency of the combustor The combustion control system may include a sensor 74 fluidly coupled to combustor 50 to detect a pressure pulse 52 within combustor Sensor 74 may be positioned at a location where pressure pulse 52 may be detected accurately without being exposed to severe environmental conditions.
Combustor 50 may include a torch igniter 62 fluidly coupled to combustor Torch igniter 62 may be configured to ignite the fuel-air mixture in combustor Torch igniter 62 may include an igniter 64 coupled to a torch access port Torch access port 63 may include a side port 66 coupled thereto. A transfer tube 68 may be coupled at one end to side port An opposite end of transfer tube 68 may be coupled to one end of a T-section Sensor 74 may be coupled to a second end of T-section 72 to measure pressure pulse A third end of T-section 72 may be coupled to a first end of a semi-infinite coil Semi-infinite coil 76 may include a tube coiled to have a generally cylindrical shape.
A drain valve 78 may be coupled to a second end of semi-infinite coil 76 , opposite the first end. Drain valve 78 may be maintained in a closed position when turbine engine is operating, and may be opened to discharge residue collected in the semi-infinite coil 76 during operation of turbine engine Semi-infinite coil 76 may serve to dissipate reflected pressure pulses in transfer tube Dissipation in semi-infinite coil 76 may prevent the reflected pressure pulses from affecting the measurements of sensor Semi-infinite coil 76 may thus serve to increase the accuracy and sensitivity of sensor 74 to pressure pulse In some embodiments, semi-infinite coil may be made of a metallic material, such as stainless steel or copper.
In general, the size and shape of semi-infinite coil may depend upon the combustion and acoustic characteristics of turbine engine In some embodiments, semi-infinite coil 76 may include a tube having a total length between about 20 feet to 60 feet and an outer diameter between about 0. However, it should be emphasized that the disclosed combustion control process is not limited by the size and shape of the semi-infinite coil For instance, in some embodiments, semi-infinite coil 76 may have the general shape of a straight tube.
In general, any structure that is capable of accentuating amplitude of pressure pulse 52 may serve as semi-infinite coil Sensor 74 may be a piezoelectric sensor configured to measure pressure pulses 52 within combustor It is contemplated that sensor 74 may include any kind of sensor known in the art that is capable of measuring pressure pulses Sensor 74 may output a signal 73 that corresponds to pressure pulse Signal 73 may be input into a signal conditioner Signal conditioner 80 may perform one or more signal conditioning operations, such as transformation of signal 73 from the time domain to the frequency domain.
Signal conditioner 80 may also include band pass filters configured to allow signals within a predefined frequency range to pass through. These predefined frequency ranges could include one or more frequency ranges that span a natural frequency of combustor An output signal 83 from signal conditioner 80 may include an electrical signal that corresponds to an amplitude of pressure pulse 52 within the predefined frequency range.
Output signal 83 may be input into a controller Controller 82 may be configured to compare output signal 83 to one or more threshold values, and perform one or more actions in response to the comparison. These threshold values may be stored in a memory of the controller 82 , or may be selected by hardware settings for instance, settings of switches or dials.
For instance, if the amplitude of output signal 83 is above a threshold amplitude, controller 82 may sound an alarm Controller 82 may also actively control turbine engine in response to a comparison. The active control may include varying the fuel supply to combustor For instance, if a comparison indicates that the amplitude of output signal is above a threshold amplitude, controller 82 may increase the amount of fuel delivered to combustor 50 through pilot As described earlier, increasing pilot fuel supply may tend to eliminate or decrease amplitude of pressure pulse 52 by increasing the temperature of the combustion flame.
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In some embodiments, controller 82 may also decrease the amount of fuel delivered to combustor through the main flow path 35 that, is the main fuel supply. In some embodiments, the increase in pilot fuel and the decrease in main fuel may be such that the total fuel supplied to combustor may be a constant. The disclosed embodiments relate to a system and a process for active combustion control of a turbine engine.
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A fuel injector delivers multiple streams of fuel and compressed air to a combustor of the turbine engine. These multiple streams include a lean premixed fuel air mixture delivered through a main flow path and a pressurized stream of fuel and air delivered through a pilot flow path. The lean premixed fuel air mixture burns in combustor at a low temperature, and thereby, produces low NO x emissions, and the stream of fuel and air burn at a relatively higher temperature to produce higher NO x emissions.
During normal operation, a majority of the fuel to combustor may be delivered through the main flow path and the turbine may operate in a low NO x emitting mode. At some operating conditions, combustion in the turbine engine may be unstable. Unstable combustion may generate pressure pulses in the combustor. A sensor fluidly coupled to the combustor may output a signal indicative of the pressure pulse in the combustor. A controller electrically coupled to the sensor may actively control the amount of fuel delivered to combustor through the main and pilot flow paths to prevent pressure pulses in combustor and minimize NO x emissions.
To illustrate an application of the disclosed combustion control process, an exemplary embodiment will now be described. Turbine engine may include a fuel injector 30 having a main flow path 35 and a pilot flow path 45 coupled to a combustor 50 of the turbine engine as shown in FIG.
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The main flow path 45 may deliver a lean premixed fuel-air mixture to combustor 50 and the pilot flow path 45 may deliver a stream of pressurized fuel and air to combustor In general, main flow path 35 may deliver a first amount of fuel to combustor 50 and the pilot flow path 45 may deliver a second amount of fuel to combustor 50 step In this fuel flow condition, turbine engine may operate in a stable combustion zone, and the NO x emission of turbine engine may be within acceptable limits. A change in load coupled to turbine engine may shift the operation of turbine engine into an unstable zone.
Unstable combustion may generate a pressure pulse 52 in combustor 50 see FIG. During the operation of turbine engine , sensor 74 coupled to transfer tube 68 , may continuously measure pressure fluctuations generated within combustor 50 to detect a changes in pressure signal as the turbine engine enters an unstable zone step Sensor 74 , thus, may measure a signal indicative of pressure pulse Sensor 74 may be electrically connected to devices that are configured to identify a pressure pulse that exceeds a threshold value.
Active Combustion Control Using a Fluidic Oscillator for Asymmetric Fuel Flow Modulation
In some embodiments, the threshold value may represent amplitude of a pressure pulse having a frequency close to a natural frequency of combustor In an exemplary embodiment, combustor 50 may have natural frequencies of Hz and Hz. In the exemplary embodiment, where two natural frequencies of turbine engine are Hz and Hz, these pre-assigned frequency ranges may be about Hz and about Hz. Signal conditioner 80 may, thus, filter noise and amplify a signal measured by sensor 74 step The filtered signal may be input into a controller 82 that may be configured to control the fuel supply to combustor One or more threshold values of amplitude may be stored in controller As described earlier, these threshold values may include a threshold amplitude of a pressure pulse 52 having a frequency within the pre-assigned frequency range of signal conditioner For instance, in previously described exemplary embodiment, signal conditioner 80 may direct output signal 83 having frequency between about Hz or about Hz to controller Controller 82 may compare the amplitude of output signal 83 with one or more threshold amplitude values stored therein step , and initiate an action in response to a result of the comparison.
If the output signal 83 is not above the one or more threshold values, the controller 82 may not initiate any corrective action, and will continue monitoring signals measured by sensor If the output signal 83 is above a threshold value, controller 82 may increase pilot fuel supply to a pre-determined value step In some embodiments, this predetermined value may be a value of pilot fuel supply that may be sufficient to stabilize the combustion process.
Stabilization of the combustion process may decrease or eliminate pressure pulse In some embodiments, increasing pilot fuel supply may change the amplitude of the pressure pulse to below the threshold value.
The pre-determined value of pilot fuel flow may be determined by computations or prior experience. In some embodiments of the active combustion control process, in addition to increasing pilot fuel supply, step may also include decreasing the main fuel supply to keep the total fuel supply to combustor 50 a constant. In some embodiments, controller 82 may initiate additional actions if an amplitude of the measured pressure pulse is above a threshold value. The additional actions may include sounding an alarm, flashing a light, or other actions designed to make an operator aware of the unstable combustion in combustor After increasing the pilot fuel supply to a pre-determined value, the controller 82 may wait for a pre-determined time step Research results NO awards, planed studies or tests, speeches, publications or trade fair participations that are based on research results!
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