INTELLIGENT CONTROL OF COMBUSTION WITH TIME SERIES AND BYPASS FILTERS AND CORRESPONDING SYSTEM

Abstract

A method for predicting a combustion error type of a combustion flame. A raw signal of an error parameter of the combustion flame within a predefined time span is measured, the error parameter is adapted for determining the combustion error type. A predefined frequency range from the raw signal is extracted using a by-pass filter, where the raw signal is decomposed. The number of peaks of the predefined frequency range within the time span is counted. An actual reference value is determined by dividing the number of counted peaks by the time span. The actual reference value is compared with a nominal reference value, wherein the nominal reference value is determined by dividing a predefined number of peaks of the predefined frequency range by the time span, so that the combustion error type is predictable if the actual reference value differs to the nominal reference value.

Claims

1. A method for predicting a combustion error type of a combustion flame burning in a combustion chamber of the combustion system for a gas turbine engine, the method comprising: measuring a raw signal of an error parameter of the combustion flame within a predefined time span, wherein the error parameter is adapted for determining the combustion error type, extracting at least one predefined frequency range from the raw signal by using at least one by-pass filter, so that the raw signal is decomposed, counting a number of peaks of the at least one predefined frequency within the time span, determining an actual reference value by dividing the number of counted peaks by the time span, comparing the actual reference value with a nominal reference value, wherein the nominal reference value is determined by dividing a predefined number of peaks of the at least one predefined frequency range by the time span, so that the combustion error type is predictable if the actual reference value differs to the nominal reference value.

2. The method according to claim 1, wherein the combustion error type is fretting of a combustion flame, a blow out of the combustion flame or a resonant frequency of the combustion flame.

3. The method according to claim 1, wherein the error parameter is combustion pressure of a combustion flame or a combustion temperature of the combustion flame.

4. The method according to claim 1, further comprising: controlling a control parameter which is adapted for controlling the combustion flame error parameter of the combustion flame so that the actual fractal time series meets the limit of the nominal fractal time series.

5. The method according to claim 4, wherein the control parameter is a main fuel/pilot fuel ratio injected into the combustion chamber.

6. A combustion system for a gas turbine engine, the combustion system comprising: measuring unit configured for measuring a raw signal of an error parameter of a combustion flame burning in a combustion chamber of the combustion system within a time span, wherein the error parameter is adapted for determining a combustion error type, a by-pass filter for extracting at least one predefined frequency range from the raw signal, so that the raw signal is decomposed a counting unit for counting a number of peaks of the at least one predefined frequency range within the time span, a determining unit for determining an actual reference value by dividing the number of counted peaks by the time span, a comparing unit for comparing the actual reference value with a nominal reference value, wherein the nominal reference value is determined by dividing a predefined number of peaks of the at least one predefined frequency range by the time span, so that the combustion error type is predictable if the actual reference value differs to the nominal reference value.

7. The combustion system according to claim 6, wherein the combustion error type is fretting of a combustion flame, a blow out of the combustion flame or a resonant frequency of the combustion flame.

8. The combustion system according to claim 6, wherein the error parameter is combustion pressure of a combustion flame or a combustion temperature of the combustion flame.

9. The combustion system according to claim 6, further comprising: a controller for controlling a control parameter which is adapted for controlling the combustion flame error parameter of the combustion flame so that the actual fractal time series meets the limit of the nominal fractal time series.

10. The combustion system according to claim 9, wherein the control parameter is a main fuel/pilot fuel ratio injected into the combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The FIGURE shows a schematical view of a combustion system for a gas turbine engine and a method for predicting a combustion error type according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0061] The illustrations in the drawings are schematically. It is noted that in different figures, similar or identical elements are provided with the same reference signs.

[0062] The FIGURE shows a schematical view of a combustion system for a gas turbine engine and a method for predicting a combustion error type according to an exemplary embodiment of the present invention.

[0063] In particular, in the FIGURE, a combustion system 100 for a gas turbine engine is presented. The combustion system 100 comprises at least one measuring unit 103 configured for measuring a raw signal of a frequency spectrum of an error parameter of a combustion flame 102 burning in a combustion chamber 101 of the combustion system 100. The error parameter is adapted for determining a combustion error type. A by-pass filter 108 is adapted for extracting at least one predefined frequency from the raw signal is provided, so that the raw signal is decomposed.

[0064] The combustion system further comprises a counting unit 109 for counting a number of peaks of the at least one predefined frequency within the time span. A determining unit is adapted for determining an actual reference value by dividing the number of counted peaks by the time span.

[0065] The combustion system 100 further comprises a comparing unit 110 for comparing the actual reference value with a nominal reference value, wherein the nominal reference value is determined by dividing a predefined number of peaks of the at least one predefined frequency by the time span, so that the combustion error type is predictable if the actual reference value differs to the nominal reference value by a predefined amount.

[0066] For example, the comparing unit 110 compares for example the actual and nominal reference value, wherein a time series analysis of the counted peaks within the time span may be conducted based on a fractal dimension. Hence, a fractal time series as reference value may be determined. Furthermore, based on the determined fractal time series, a Hurst exponent may be determined. In an example, a typical nominal value (limit) under H (Hurst exponent)<0.5 would indicate that the system becomes unstable, H<0.3 could be used a warning trigger, whilst the H<0.15 may be used as a corrective action. Hence, if H<limit, corrective action would be done in step 111. If H>limit, no corrective action would be done in step 112 and the gas turbine operation would be continued.

[0067] Furthermore, the FIGURE shows a method according to the invention which can be conducted by the above described combustion system 100. The method is adapted for predicting a combustion error type (e.g. fretting) of the combustion flame 102 burning in the combustion chamber 101 of the combustion system 100 for a gas turbine engine. The method comprises the step of measuring a raw signal of a frequency spectrum of an error parameter (e.g. pressure, temperature) of the combustion flame 102 within a predefined time span, wherein the error parameter is adapted for determining the combustion error type. Furthermore, the method comprises an extracting at least one predefined frequency from the raw signal by using the by-pass filter 108, so that the raw signal is decomposed. In a further step, the number of peaks of the at least one predefined frequency range within the time span is counted. Furthermore, in a further step, an actual reference value is determined by dividing the number of counted peaks by the time span. Finally, in a further step, the actual reference value is compared with a nominal reference value, wherein the nominal reference value is determined by dividing a predefined number of peaks of the at least one predefined frequency by the time span, so that the combustion error type is predictable if the actual reference value differs to the nominal reference value.

[0068] The combustion chamber 101 of the combustion system 100 comprises an e.g. a pre-combustion zone and a main combustion zone. The combustion flame 102 occurs in the pre-combustion zone and the main combustion chamber. A fuel is split with a controllable pilot fuel/main fuel ratio into a pilot fuel mass flow within a pilot fuel line 107 and a main fuel mass within a main fuel line 106. The pilot fuel is injected at a pilot burner inside the pre-combustion chamber. The main fuel is injected together with the air through a swirler prior to the pre-combustion zone 101. The pilot fuel is generally richer fuel for maintaining and controlling a stable flame inside the combustion chamber 101. The main fuel is generally leaner than the pilot fuel in order to ensure an optimum burning characteristic, i.e. with low emissions, such as NOx.

[0069] Depending on e.g. the load of the gas turbine and the pilot fuel/main fuel ratio, combustion error types of the combustion flame may occur. A combustion error types may be for example resonant frequencies of the combustion flame 102 resulting in fretting of the combustion chamber or other hardware, or a blow out of the combustion flame.

[0070] Each combustion error type may be determined on its individual error parameter. In particular, an oscillation pattern of an error parameter (i.e. the frequency of the error parameter) may be indicative for a certain combustion error type.

[0071] The error parameter may be for example a combustion pressure of the combustion flame 102 or a combustion temperature of the combustion flame. In particular, the error parameter may be a pattern of hot spots of a combustion chamber wall heated by the combustion flame 102 within the combustion chamber 101, for example.

[0072] A predefined frequency of a raw signal of the error parameter is measured. A predefined frequency is extracted from the raw signal by using the by-pass filter 108, so that the raw signal is decomposed. Each error combustion error type can be detected on the basis of a specific predefined frequency extracted from a measured frequency spectrum of an error parameter. For example, if the error parameter is the pressure of the combustion flame 102, the oscillation of the pressure defines the predefined frequency spectrum. For example, if the error parameter is the location of temperature maxima of the combustion flame 102, the oscillation of the location of temperature maxima of the combustion flame defines the predefined frequency spectrum.

[0073] If e.g. fretting of the combustion flame 102 occurs, a certain behaviour (e.g. amplitude, frequency pattern etc.) of a specific predefined frequency of the frequency pattern exists. Specifically, a number of peaks within the time span of the predefined frequency are indicative of a behaviour of an combustion error type.

[0074] The actual reference value represents the peaks measured within a time span independently from any periodic behaviours of the frequency. A peak may be defined as a local maximum of a value of an amplitude of the predefined frequency. The value of the amplitude forming a local maximum may be defined in advance.

[0075] For example, if a value of the amplitude exceeds a predefined threshold value, each exceeding of the threshold value forms a peak to be counted. The peaks may be counted, if a local maximum of the amplitude is reached and the local maximum is above the threshold value. Each local maximum forming a peak is counted within the time span.

[0076] The nominal reference value represents the predefined number of peaks of an amplitude of a predefined within the time span. The nominal reference value refers to a number of peaks within the time span which are predetermined e.g. under laboratory conditions. The nominal reference value determines a threshold value, wherein a reference value below the nominal reference value is indicative of stable operation of the gas turbine, i.e. where the risk of occurrence of the respective combustion error type is low. A reference value above the nominal reference value is indicative of an instable operation of the gas turbine, i.e. where the risk of occurrence of the respective combustion error type increases rapidly or is high.

[0077] The nominal reference value may be stored in a data basis in a storage unit, for example. Furthermore, a plurality of nominal reference values for certain operating states and error parameter (e.g. pressure, temperature) may be stored and used to predict a combustion error type.

[0078] According to the invention, the respective combustion error type is predicted, if the actual reference value differs to the nominal reference value. For example, if the actual reference value exceeds the nominal reference value, a respective combustion error type is predicted. Furthermore, a range from the nominal reference value may be defined, so that a respective combustion error type is predicted if the actual reference value exceeds the nominal reference value by a predefined threshold value and/or by a predefined threshold time span.

[0079] By presenting the predefined frequency from the raw signal with an actual reference value, a typical behaviour of a combustion error type at an onset, i.e. at the start of the combustion error type is determinable and hence the combustion error type is better predictable.

[0080] A control parameter which is adapted for controlling the combustion flame error parameter of the combustion flame 102 is controlled so that the actual reference value meets the limit of the nominal reference value and so that the risk of a combustion error type is reduced.

[0081] The control parameter is for example a main fuel/pilot fuel split ratio injected into the combustion chamber 101 or a general mass flow of the fuel into the combustion chamber 101. The control parameter could also be a control of the amount of bleed of compressor air of the gas turbine, a control of the Variable Guide Vane (VGV) position of the gas turbine or engine speed of the gas turbine.

[0082] The above-described units, such as the counting unit 109, the comparing unit 110 and the determination unit may comprise a microprocessor for processing the received data.

[0083] The above described units 108, 109, 110 may be part of an (engine) control unit 104 of the combustion system 100. The control unit 104 accordingly conducts the steps of the above described method. Additionally, the control unit 104 controls e.g. the actions for driving the combustion chamber 101 and in particular to prevent combustion error types. Therefore, the control unit 104 may be connected to operating units, such as a fuel control unit 105, for example a controllable valve, which controls the fuel supply into the combustion chamber. In particular fuel control unit 105 controls the main fuel/pilot fuel ratio.

[0084] The measuring unit 103 may be for example a temperature sensor, a pressure sensor, an optical sensor and/or a sound sensor. In particular, the measuring unit 103 may comprise for example pressure sensors for measuring a pressure oscillation of the combustion flame or temperature sensors for measuring hot spots and a temperature pattern of the combustion flame 102. The temperature sensor measures the temperature of the hot products, i.e. the exhaust gas, inside the combustion chamber 101. The temperature sensor is for example arranged closed to or at the hottest location inside the combustion chamber 101 or is located further downstream of the combustion chamber 101.

[0085] It should be noted that the term comprising does not exclude other elements or steps and a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

[0086] 100 combustion system [0087] 101 combustion chamber [0088] 102 combustion flame [0089] 103 measuring unit [0090] 104 control unit [0091] 105 fuel control unit [0092] 106 main fuel line [0093] 107 pilot fuel line [0094] 108 by-pass filter [0095] 109 counting unit [0096] 110 comparing unit [0097] 111 correcting engine operation [0098] 112 continuing engine operation