CN116557149A - Online diagnosis method for oscillation combustion of aero-engine combustion chamber - Google Patents
Online diagnosis method for oscillation combustion of aero-engine combustion chamber Download PDFInfo
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Abstract
The invention provides an on-line diagnosis method for oscillation combustion of an aero-engine combustion chamber, and relates to the field of combustion stability test of the aero-engine combustion chamber. The method realizes on-line diagnosis of the oscillation combustion state of the combustion chamber of the aeroengine by taking the multi-scale kurtosis as a diagnosis index. At present, short-time Fourier transformation of pressure pulsation of a combustion chamber is generally adopted as a diagnosis index of the combustion state of the combustion chamber in diagnosis of the oscillating combustion state, however, the method can only give out frequency spectrum, the relative magnitude of pulsation amplitude often needs to be manually identified, and the combustion state is difficult to be given out on line in real time. The on-line diagnosis method for the oscillation combustion of the aero-engine combustion chamber can accurately and rapidly judge the current combustion state on line, and solves the problem that the oscillation combustion state is judged by relying on the average pressure of the combustion chamber in the prior art.
Description
Technical Field
The invention relates to the field of measurement of unstable combustion of an aero-combustion chamber, in particular to an on-line diagnosis method for oscillating combustion of an aero-engine combustion chamber.
Background
Unstable combustion phenomenon often occurs, and prevention and inhibition of unstable combustion state have important significance for engine and flight safety. In the development process of the combustion chamber component, on-line monitoring of an unstable combustion state in a test is urgently needed, and support is provided for test safety, state analysis and design optimization in time.
In engineering experiments, the combustor dynamic pressure or acoustic pressure signal is the most readily available unstable signal. It is therefore the most appropriate way to obtain the unstable-state criterion from the DP signal. Unstable combustion conditions in the combustion chamber involve two actions: combustion instability (Combustion Instability: CI) and flame instability (Flame Instability: FI). The former describes a coupled phenomenon of combustion heat release rate and sound vibration, namely positive feedback is formed among the heat release rate pulsation, the sound pulsation and the oil-gas ratio pulsation, which is also called oscillation combustion. When CI occurs, a large-amplitude pressure wave can appear in the combustion chamber, and the damage to the engine body is extremely easy to cause. The latter describes the flame moving away from its steady state, toward a misfire, flameout or flashback. In low pollution combustors, FI misfires are prone to occur because the operating conditions are typically lean; FI is easy to occur when the engine is under variable working conditions, so that the engine is flameout in the air, re-ignition is required, and the engine is extremely harmful to the operation of the engine body. From the mechanism of CI generation, FI is often its provoking source, which may result in CI if FI does not cause flameout.
In the prior art, short-time Fourier transformation of pressure pulsation of a combustion chamber is mostly adopted as a diagnosis index of the combustion state of the combustion chamber, however, the method can only give a frequency spectrum, and the relative magnitude of the pulsation amplitude often needs to be manually identified.
Disclosure of Invention
In order to solve the problems, the invention provides a basis and means for optimizing the thermo-acoustic stability performance of the aero-engine by expanding an online diagnosis method in a combustion stability test of a combustion chamber, and provides an online diagnosis method for the oscillating combustion of the combustion chamber of the aero-engine.
An on-line diagnosis method for the oscillating combustion of an aeroengine combustion chamber is characterized in that for a combustion chamber pulsating pressure signal P ', an on-line diagnosis method for the oscillating combustion of the aeroengine combustion chamber is formed according to the multi-scale kurtosis K of P' as a diagnosis index of the oscillating combustion;
the method specifically comprises the following steps:
step 1: an oscillation combustion experiment system is established so as to be capable of acquiring a combustion chamber P' on line;
step 2: setting a window length delta t;
step 3: calculating instantaneous kurtosis
Step 4: calculating the average kurtosis
Step 5: calculating intermittent kurtosis
Step 6: and judging whether the combustion chamber is in an oscillating combustion state or not according to the parameters.
Further, the multi-scale kurtosis includes a transient kurtosis, an average kurtosis, and a resting kurtosis; the calculation of kurtosis depends on the selection of the time window length.
Further, the window length in step 2 means that when calculating the kurtosis index, N signal points with a time length Δt need to be processed.
Further, the transient kurtosis described in step 3The method is to count the average kurtosis by using the data in the length n of a fixed time window to form the instantaneous kurtosis; the instantaneous kurtosis of the signal p (t) at a certain instant τ takes the form of the front δt p N data points in the duration are counted, and the statistical formula is as follows:
further, the average kurtosis described in step 4When the working condition is identified, the average kurtosis is adopted for representing the whole working condition under the condition that the working condition parameters are unchanged; the average kurtosis is defined as the time scale delta t for the signal p (t) during positive operating conditions p The whole working condition interval is translated to obtain the average value of m instantaneous kurtosis, and the formula is as follows:
FI is often the cause of CI in actual unstable combustion processes, and thus FI and CI are often intermixed during typical unstable combustion evolution. Such clutter manifests itself as a high frequency CI signal carried on a low frequency FI signal.
Further, the intermittent kurtosis described in step 5Is to define a certain time point amplitude s i For the maximum value minus the minimum value of the signal p (t) in the waveform period before this time, the formula is as follows:
s i ＝p max -p min (3)。
further, in the digital signal processing, the processing mode of the one waveform period is as follows:
1) Signal p is first normalized: subtracting the average value from all signals to obtain p';
2) Traversing to a position where the p' value changes from negative to positive as a starting point i of a period;
3) Then, the position of the next p' from negative to positive is found to be used as an end point j;
4) Calculating the maximum value and the minimum value among i-j, and calculating the amplitude s i ；
5) The time series of all amplitude formations is calculated as intermittent average kurtosis according to (2)Further, the step 6 of judging whether the combustion chamber is in the oscillation combustion state refers to directly performing kurtosis analysis on the DP signal, and the step 6 is +.>And->Meaning that FI is unstable, it is highly likely that CI will be triggered later, which can be used as early warning for CI; />In the CI state, at this time->Is affected by CI and is not used as a criterion.
Further, the selecting method of the time window length comprises the following steps:
the kurtosis calculation value depends on a time scale, so that the calculation of DP and intermittent kurtosis signals needs to give reasonable time scales of δt as δt_p and δt as δs to make sense, and therefore, the determination of the optimal time scale is the value of influencing the parameter as a criterion index. Since the physical processes reflected by both CI and FI are different, the time scale needs to be determined from the respective features. FI is much lower in frequency than CI, so FI time scale is much larger than CI time scale to detect FI features. The shorter the time scale is, the more intense the pulsatility of the calculation result is, which is not beneficial to the recognition of working conditions; otherwise, the pulsation of the result is reduced, the smoothness of the output result is better, and the working condition identification is facilitated. However, the larger the time scale is, the sensitivity to the working condition is reduced, the predicted advance is reduced, and the early warning value is even lost.
Further, the method for selecting the time window length uses scale independence to determine the optimal time length: the time scale is gradually increased from a smaller time scale to a time scale when the statistical result is not changed greatly as an optimal value.
Further, the oscillating combustion experimental system in step 1 refers to a system comprising a test piece, an air supply and exhaust system, a fuel supply system, an ignition system, a signal measurement system and the like. In the signal measurement system, the system comprises a dynamic pressure sensor, a high-speed digital acquisition system, a computer, a signal acquisition interface and the like which are arranged at reasonable positions of the combustion chamber. The sampling frequency of the signal acquisition system is greater than 4 times of self-oscillation combustion frequency.
The invention has the beneficial effects that:
1. in the process of the oscillation test of the combustion chamber of the aero-engine, the invention can accurately and rapidly judge the current combustion state on line;
2. the problem of rely on combustion chamber average pressure to judge oscillation combustion state among the prior art is solved.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of an unstable combustion test system of the present invention.
FIG. 2 shows the different δt of the G-type combustor of the present invention p At the scale ofIs a schematic diagram of (a).
FIG. 3 shows the G-type combustor of the present invention at different scale factors rIs a schematic diagram of (a).
FIG. 4 is a schematic view of the combustion chamber DP and its distribution under several exemplary combustion conditions of the present inventionWherein (a) is a stable combustion state,(b) Is CI state (JavaScript)>(c) Is in the FI fire-relieving state, and is a part of>(d) Is in the CI state with the fire relieving effect of FI and the CI state with the fire relieving effect of +.>
FIG. 5 is a schematic diagram of the calculation of amplitude timing in accordance with the present invention, wherein (a) is the amplitude timing statistics; (b) amplitude timing statistics and amplitude distribution.
FIG. 6 is a schematic representation of the variable equivalence ratio continuous DP signal for the G combustor of this invention.
FIG. 7 is a schematic diagram of the inventive G combustor variable equivalence ratio continuous transient kurtosis, wherein (a) DP and transient pressure kurtosis; (b) DP and transient intermittent kurtosis.
FIG. 8 is a schematic diagram of the measurement layout of the unstable combustion state diagnostic test of the L-shaped combustion chamber of the present invention.
FIG. 9 is a schematic of the L combustor variable equivalence ratio continuous DP signal of the present invention.
FIG. 10 is a schematic diagram of the L combustor variable equivalence ratio continuous transient kurtosis of the present invention, where (a) is DP and transient pressure kurtosis; (b) DP and transient intermittent kurtosis.
Reference numerals illustrate: 1. an intake pressure measurement point; 2. a fuel inlet; 3. a combustion chamber pressure measurement point; 4. CH fluorescence intensity measurement.
Detailed Description
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
An on-line diagnosis method for the oscillating combustion of the combustion chamber of an aeroengine is formed by taking the multi-scale kurtosis K of a combustion chamber pulse pressure signal P' as a diagnosis index of the oscillating combustion aiming at the combustion chamber. The method comprises the following specific steps:
step 1: an oscillation combustion experiment system is established, and comprises a test piece, an air supply and exhaust system, a fuel oil supply system, a signal measurement system and the like, as shown in fig. 1. In the signal measurement system, the system comprises a dynamic pressure sensor, a high-speed digital acquisition system, a computer, a signal acquisition interface and the like which are arranged at reasonable positions of the combustion chamber. The sampling frequency of the signal acquisition system is greater than 4 times of self-oscillation combustion frequency.
Step 2: setting the window length; the invention uses scale independence to determine the optimal length of time: the time scale is gradually increased from a smaller time scale to a time scale when the statistical result is not changed greatly as an optimal value. If the value is larger than the value, the early warning value is not high, the value is smaller than the value, the signal pulsation is large, and the online early warning is not facilitated. In the invention, based on the phenomenon that FI appears before CI generation, the possibility of the occurrence of the subsequent CI can be predicted through the identification of the FI, thereby providing early warning.
FIG. 2 shows different δt p At the scale ofRespectively take δt p Calculation results at=0.01 s, 0.025s, 0.05s, 0.075s and 0.1 s. It can be seen that at 0.01s and 0.025s, the fluctuation is severe in the non-CI section (0 s-2 s) and smooth in the CI section (2 s-). The invention therefore uses the difference in CI segments as a criterion when δt p The CI segment values for the three time scales after =0.05 are substantially close and follow δt p The increase of the non-CI pulse is reduced, which is beneficial to FI state discrimination. It can be concluded that the time scale has less impact when in the CI state; in the non-CI state, the larger the time scale, the smaller the kurtosis value ripple. From FIG. 2, δt is selected in the present invention p As a calculation scale of DP kurtosis, =0.1, the smoothness of diagnosis can be obtained.
As mentioned above, the frequency of FI is far lower than that of CI, so that the reasonable intermittent kurtosis value of the FI characteristic is obtained, the time scale of the FI characteristic is larger than that of the pressure kurtosis value of DP, and the invention adopts a multiple relation: δt s ＝rδt p R.gtoreq.1 to determine δt s . In order to obtain a suitable magnification r, a similar scale-independent method is also employed. FIG. 3 shows the combustion chamber at different scale factors rTaking r=1, 2, 3, 4, 5 and 6, respectively, to obtain intermittent kurtosis. When r is relatively small, its value is +.>The influence of (2) is large and the pulsation is also large. When r=4, 5 and 6, three lines (thick lines) in the graph are relatively close, and r=5 is selected as a reasonable multiplying power to calculate the intermittent kurtosis.
Step 3: calculating instantaneous kurtosisThe data over a length n of the fixed time window is used to calculate the average kurtosis to form the instantaneous kurtosis (Temporal Kurtosis: TK). The instantaneous kurtosis of the signal p (t) at a certain instant τ takes the form of the front δt p Statistics are performed on n data points in the duration, and the statistics are shown in a formula (1).
Step 4: calculating the average kurtosisThe average kurtosis is characterized by adopting the average kurtosis for the whole working condition with the unchanged working condition parameters when the working condition is identified. The average kurtosis is defined as the time scale delta t for the signal p (t) during positive operating conditions p And (3) translating the whole working condition interval to obtain an average value of m instantaneous kurtosis, wherein the average value is shown in the formula (2).
The combustion chamber DP and its distribution in several typical combustion conditions are shown in fig. 4. FI is often the cause of CI in actual unstable combustion processes, and thus FI and CI are often intermixed during typical unstable combustion evolution. Such clutter manifests itself as a high frequency CI signal carried on a low frequency FI signal. It is difficult to give FI characteristics if the average DP kurtosis of the same scale is used alone as a diagnostic parameter.
Fig. 4 shows several exemplary conditions of the DP signal in the combustion chamber. The total duration of each group of test data is 8s, the sampling rate is 2kHz, and 16k data points are obtained; the left side of the graph is the DP time sequence with the duration of 1s, the right side is the pressure probability distribution with the duration of 8s, the histogram is the statistical value, and the solid line is the normal distribution fit. Its average kurtosisThe 8s average value calculated according to the formula (4), that is, the deviation from the normal distribution. Wherein: (a) To stabilize the combustion state, the signal is substantially close to a random signal from the pdf distribution,(b) In CI state, the signal shows stronger unimodal form in the frequency domain, pdf deviates far from normal distribution, ++>This value and literature [23] The values of (a) are consistent (the two definitions differ); (c) Flame blow-off conditions (FI) which occur in low-power combustion, the low-frequency characteristics of the signal being relatively pronounced, which are +.>The degree of deviation from normal distribution is less than CI; (d) CI and FI mixed conditions, lean in high power combustion conditions, tend to occur. Appears to carry high frequency ripple (CI) on the low frequency intermittent basis (FI). In the case of a normal unstable combustion and a transition between combustion states, the d state is frequently present. Status->This value indicates that its state ratio b is stable. From CI componentThe amplitude ratio b is smaller, and the conclusion is true; but from the waveform, the flame intermittence is very strong, the image is observed to be in a strong fire-out state, and is the leading characteristic for triggering the subsequent CI, and is a signal which needs special attention of an early warning system, but adopts +.>It is difficult to separate the states.
In a stable combustion stateNear normal distribution; in CI state, javaScript> Has better differentiation degree; but in FI state->The degree of such instability cannot be clearly described, i.e. it is difficult to cover two instabilities with one parameter, and the two instabilities cannot be distinguished using a single scale kurtosis feature. From Nair and the experiments described later, the characteristic frequency of FI is an order of magnitude smaller than CI, and the time scale for CI cannot contain multiple cycles of FI. The instability of CI is represented on the DP amplitude, and the frequencies of all time periods are basically consistent under the same working condition; instability of FI appears as intermittent in DP: the pressure amplitude varies greatly over the period; the kurtosis characteristic of the salient FI should therefore be reflected in an intermittent variation of the amplitude.
Step 5: calculating intermittent kurtosisDefining a time point amplitude s i The maximum value of the signal p (t) in the waveform period before the moment is reduced by the minimum value, as shown in formula (3).
In digital signal processing, so-called one cycleThe processing mode is as follows: 1) Signal p is first normalized: subtracting the average value from all signals to obtain p'; 2) Traversing to a position where the p' value changes from negative to positive as a starting point i of a period; 3) Then, the position of the next p' from negative to positive is found to be used as an end point j; 4) Calculating the maximum value and the minimum value among i-j, and calculating the amplitude s i The method comprises the steps of carrying out a first treatment on the surface of the 5) The time series of all amplitude formations is shown in figure 5. Calculating intermittent average kurtosis according to (2)
The average calculation was performed for a period of 8s for the three typical conditions in fig. 4, and the results are shown in table 1.Sensitivity to FI instability and positive correlation; in the d state, < > and >>More closely approach the literature [17] Is a fire escape value of (2). />Sensitivity to CI and positive correlation, in d-state +.>In a non-CI state, the d state is comprehensively judged to be the FI fire-out as a main characteristic, and at the moment, the early warning system can trigger an alarm to predict the CI state with the subsequent high probability. Therefore, on signal real-time diagnosis, the two signals can be adopted to cooperate to determine the combustion state: />In the CI state, the larger the value is, the stronger the CI state is; when->Based on->Judging the FI state (including->The fire out state, the greater the value the stronger the FI state. As will be seen hereinafter, inWhen (I)>The meaning is ambiguous because it is subject to +.>The influence of (2) is large.
Since the characteristic frequency of FI is an order of magnitude smaller than CI, the invention calculates DP kurtosis and intermittent kurtosis on two time scales, respectively, at δt p Kurtosis reflecting CI features is defined on scaleAt δt s The kurtosis reflecting the FI characteristic is defined by amplitude timing on scale>The invention defines the intermittent time scale to be δt p Is a multiple of (2): δt s ＝rδt p Where the size of r needs to be determined by establishing rules, r=5 after optimization.
TABLE 1 DP kurtosis under typical operating conditionsAnd intermittent kurtosis->
Step 6: in a combustion stateAnd->Meaning that FI is unstable, it is highly likely that CI will be triggered later, which can be used as early warning for CI; />In the CI state, at this time->Is affected by CI and is not used as a criterion.
The following describes the embodiments of the present invention further with reference to the drawings.
Example 1: gaseous fuel double swirl diffusion flame (G combustion chamber)
Step 1: the experimental system is designed and laid out as shown in fig. 1, and mainly comprises an air inlet section, a combustion section and an exhaust section. The air needed for combustion is supplied by the fan, and the air inflow is changed by adjusting the rotating speed of the fan. The average velocity of the air was measured using a hot wire anemometer at the mid-intake section. Air enters the combustion chamber through a two-stage axial swirler through a pipe having an outer diameter dair=50 mm. Propane fuel enters the combustion chamber through 12 jet holes in the circumferential direction from the center of the swirler through a central pipe of diameter dfuel=12 mm. The combustion chamber is square in cross section and has a side length of l=100 mm. Combustor length a=300 mm. The side of the combustion chamber is provided with a quartz glass observation window, a high-speed photographic camera is used for shooting flame image signals, and four measuring holes are formed in the top of the combustion chamber for measuring DP signals in the combustion chamber. The back of the combustion chamber is provided with a photomultiplier with a CH filter to collect the CH intensity change and characterize the change of the heat release rate in the combustion chamber. The fuel flow is controlled by an AST10-H thermal gas mass flow controller.
FIG. 6 is a G combustor variable operating mode continuous DP signal, taking the 11s change. About 2s before a steady combustion state, where the equivalent weight is higher and the DP amplitude is lower; the equivalence ratio was adjusted down from about 1s position in the signal until flameout was about 10.7 s. In the combustion phase, the highest DP amplitude is 5 times that at steady combustion.
Step 2: the window length is set according to the method described above, and δt is selected according to the invention p As a calculation scale of DP kurtosis, stability of diagnosis can be obtained, and r=5 is selected as a reasonable magnification to calculate intermittent kurtosis.
Step 2: calculating the instantaneous kurtosis according to the method
Step 3: calculating the average kurtosis according to the method described aboveThe subscript tau here refers to the variation of each calculation window data with on-line diagnosis time;
step 4: calculating intermittent kurtosis according to the methodThe subscript tau here refers to the variation of each calculation window data with on-line diagnosis time;
FIG. 7 shows the calculated instantaneous pressure kurtosis defined by equation (2) and equation (3)And intermittent kurtosis-> Using time scale δt p Calculated mean =0.1 s, two +.>The point interval time is δt p /4；/>Calculation needsLonger time scale δt s ＝5δt p The method comprises the steps of carrying out a first treatment on the surface of the The kurtosis values shown in FIG. 7 are median filtered values, filtering the pulsatility in the original kurtosis values, and acting to smooth the signal.
From the DP signal, after about 1s, the pressure wave appears to be more significantly intermittent: fluctuation unevenness occurred between 1s-2 s. At this point, the flame appears unstable from video, but at this point the pressure amplitude is low and no significant combustion noise is present, i.e., no CI occurs. FIG. 7.a 1s-2sThe non-CI state is also marked (in the figure +.>) The method comprises the steps of carrying out a first treatment on the surface of the However, the flame is unstable and then a higher pressure amplitude after 2s is initiated, i.e. CI occurs. From +.7 in FIG. 7.B>The FI phenomenon between 1s and 2s can be clearly identified, this period +.>Is significantly higher than the earlier stage state and +.>I.e. FI fire-free state (in the figure +.>). During the equivalence ratio down-regulation after 2s, the DP amplitude increases first, then decreases: the effect of lean oil on CI is reflected. During this process, < > before 10.7s of extinction>The description remains in CI state at all times; this stageThe result is fluctuatedAccording to the above analysis, when->When CI is unstable, the method can be used for marking CI unstable, and the method is used for marking CI unstable>The value is not used as the combustion state judgment mark. Note that: when approaching flameout, t=10.65 s in fig. 10.A, < >>At this time->According to the criterion, the fire is in the FI fire-free state; at this time, the unstable state just before flame extinction, CI disappears, and FI instability dominates. It has proven to be effective to use these two parameters to form a combined criterion.
Example 2: aviation kerosene fuel premixing pre-evaporation low pollution combustion chamber (L combustion chamber)
Because the specific implementation method of the on-line diagnosis is the same as that of the G combustion chamber, the detailed description is omitted here. It is noted that fig. 8 shows an L-combustor unstable combustion state diagnostic test measurement layout. The test was performed under normal temperature and pressure. Air is sent in by the Roots blower, enters the electric heater through the stabilizing section and then enters the combustion chamber. The diameter of the exhaust pipeline of the combustion chamber outlet is the same as the inner diameter of the flame tube of the combustion chamber. The frequency of the fan is adjusted through the frequency converter to control the air inflow, and a differential pressure flowmeter is arranged in front of the heater to measure the air flow. The fuel is aviation kerosene, and is fed through an oil pump, and the oil quantity of a nozzle is calibrated by pressure difference. The single-head LPP model combustion chamber comprises a primary radial main stage cyclone and a two-stage axial class cyclone, wherein the inner diameter is 136mm, and the length is 197.5mm. The combustion chamber is provided with an observation window and a dynamic pressure measurement opening, the heat release rate is measured through CH, and meanwhile, a flame dynamic image is shot by a high-speed CCD.
FIG. 9 is a variable operating mode continuous DP signal for an L combustor, taking a 50s change. At 5s, the equivalence ratio was reduced to 2CI occurs at 2s and reaches maximum amplitude directly. A significant intermittence of the DP waveform can be seen between 5s-22s, at which point the image observes a significant blow-off condition of the flame. FIG. 10.A showsBut with a majority of values +.>A small fraction has a value slightly greater than 1 (12 s-22s, at this time CI early stage); from 10. B->FI instability of 5s-22s is clearly identified: />In the CI phase of the section 22s-44.55s,/i>The unstable state of combustion is clearly identified. Also in the near flameout case->But->Indicating that CI disappeared and FI was the main phenomenon for a short period of time near flameout.
Claims (9)
1. An on-line diagnosis method for the oscillating combustion of an aeroengine combustion chamber is characterized in that for a combustion chamber pulsating pressure signal P ', an on-line diagnosis method for the oscillating combustion of the aeroengine combustion chamber is formed according to the multi-scale kurtosis K of P' as a diagnosis index of the oscillating combustion;
the method specifically comprises the following steps:
step 1: an oscillation combustion experiment system is established so as to be capable of acquiring a combustion chamber P' on line;
step 2: setting a window length delta t;
step 3: calculating instantaneous kurtosis
Step 4: calculating the average kurtosis
Step 5: calculating intermittent kurtosis
Step 6: and judging whether the combustion chamber is in an oscillating combustion state or not according to the parameters.
2. The on-line diagnostic method for oscillatory combustion of an aircraft engine combustor of claim 1, wherein the multi-scale kurtosis comprises an instantaneous kurtosis, an average kurtosis, and a resting kurtosis; the calculation of kurtosis depends on the selection of the time window length.
3. The on-line diagnosis method for the oscillating combustion of the combustion chamber of the aeroengine according to claim 1 or 2, wherein the window length in the step 2 means that when the kurtosis index is calculated, the N signal points with the time length of Δt need to be processed.
4. An on-line diagnostic method for oscillatory combustion of an aircraft engine combustor as claimed in claim 3, wherein the transient kurtosis in step 3The method is to count the average kurtosis by using the data in the length n of a fixed time window to form the instantaneous kurtosis; the instantaneous kurtosis of the signal p (t) at a certain instant τ takes the form of the front δt p N data points in the duration are counted, and the statistical formula is as follows:
5. the on-line diagnostic method for oscillatory combustion of an aircraft engine combustor as claimed in claim 4, wherein the average kurtosis in step 4When the working condition is identified, the average kurtosis is adopted for representing the whole working condition under the condition that the working condition parameters are unchanged; the average kurtosis is defined as the time scale delta t for the signal p (t) during positive operating conditions p The whole working condition interval is translated to obtain the average value of m instantaneous kurtosis, and the formula is as follows:
6. the on-line diagnostic method for oscillatory combustion of an aircraft engine combustor as claimed in claim 5, wherein the intermittent kurtosis is as described in step 5Is to define a certain time point amplitude s i For the maximum value minus the minimum value of the signal p (t) in the waveform period before this time, the formula is as follows:
s i ＝p max -p min (3)。
7. the on-line diagnostic method for the oscillating combustion of an aircraft engine combustion chamber of claim 6, wherein in the digital signal processing, the processing mode of the one waveform period is as follows:
1) Signal p is first normalized: subtracting the average value from all signals to obtain p';
2) Traversing to a position where the p' value changes from negative to positive as a starting point i of a period;
3) Then, the position of the next p' from negative to positive is found to be used as an end point j;
4) Calculating the maximum value and the minimum value among i-j, and calculating the amplitude s i ；
5) The time series of all amplitude formations is calculated as intermittent average kurtosis according to (2)
8. The on-line diagnosis method for oscillating combustion of aero-engine combustion chamber as set forth in claim 7, wherein said determining in step 6 whether the combustion chamber is in an oscillating combustion state is to directly perform kurtosis analysis on the DP signal in the combustion stateAnd->Meaning that FI is unstable, it is highly likely that CI will be triggered later, which can be used as early warning for CI; />In the CI state, at this time->Is affected by CI and is not used as a criterion.
9. An on-line diagnostic method for the oscillating combustion of an aircraft engine combustion chamber according to claim 8, wherein the time window length selection method uses scale independence to determine the optimal time length: the time scale is gradually increased from a smaller time scale to a time scale when the statistical result is not changed greatly as an optimal value.
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