A test method for identifying dynamic characteristic parameters of an engine

Abstract

The application belongs to the field of aero-engine test, and particularly relates to a test method for identifying dynamic characteristic parameters of an engine, wherein the test is performed when the temperature T2 at the inlet of the compressor is within a preset temperature range, the engine throttle lever is adjusted so that the engine is at a step point rotating speed, and a fuel step test is started; after the parameters are stable, a step command of a preset fuel step amount is sent to the engine by a host computer; after each step of the engine is completed and the parameters are stable, the command sent by the host computer is cancelled, the rotating speed is restored to a state corresponding to the current throttle lever, after the state of the engine is stable, the step command is continuously sent, and a fuel negative step test at the current rotating speed is started; the test can be designed in a simulation calculation mode, so that the safety of the test run and the effectiveness of the identified data are ensured.

Description

Technical Field

[0001] This application belongs to the field of aero-engine testing, and specifically relates to a test method for identifying engine dynamic characteristic parameters. Background Technology

[0002] To perform forward design work such as closed-loop parameter design and stability domain analysis of the control system, accurate engine time constants and gain coefficients are required. Obtaining accurate engine time constants and gain coefficients through engine dynamic characteristic identification experiments is essential. This experiment requires open-loop fuel flow tests at different engine speeds. To ensure the safety and validity of the test results, and to avoid errors in the calculation results caused by excessively large fuel flow step values ​​leading to deviations from linearity or excessively small flow step amplitudes resulting in significant interference from signals, simulation analysis is needed to determine the appropriate step amplitude for open-loop fuel flow control.

[0003] Meanwhile, because this test involves open-loop control of engine fuel flow, different inlet temperatures T2 will result in different speed changes due to the same fuel flow step amplitude. Therefore, special attention needs to be paid to the protection function against engine speed over-limit.

[0004] Currently, the identification of dynamic characteristic parameters of an engine mainly relies on obtaining small step data from engine models or small step test data generated during full-engine testing; however, existing technologies have the following drawbacks:

[0005] 1. The dynamic characteristic parameters of the engine are obtained through the engine model. However, since the engine model itself is different from the engine, the data obtained, especially the dynamic data, has a certain degree of inaccuracy.

[0006] 2. If small-step data from the whole-machine test process is used, there will be some disturbances due to the closed-loop control system of the controller, which are not characteristics of the engine itself.

[0007] 3. The small step data during the whole machine test may deviate too much because it is not a special test for identification. The obtained data may not meet the linear state required for identification. Summary of the Invention

[0008] To address the aforementioned shortcomings, this invention proposes an open-loop fuel flow test method. This method conducts open-loop fuel flow tests at different engine speeds. To ensure the safety and validity of the test results, and to avoid errors in the calculation results caused by excessively large fuel flow step values ​​leading to deviations from linearity or excessively small flow step amplitudes resulting in significant interference from signals, simulation analysis was conducted to determine the appropriate step amplitude for open-loop fuel flow control. Simultaneously, the influence of A2 and T2 variations on engine dynamic characteristic parameters was considered, ensuring both test safety and the validity of the identified data.

[0009] Specifically, as described below, a test method for identifying engine dynamic characteristic parameters includes:

[0010] The test was conducted with the compressor inlet temperature T2 within the preset temperature range. The engine throttle lever was adjusted to bring the engine to the step point speed, and the fuel step test was started.

[0011] Once the parameters stabilize, a step command for a preset fuel step amount is sent to the engine via the host computer.

[0012] After each step change in the engine speed and the parameters stabilize, the command issued by the host computer is canceled, the engine speed is restored to the state corresponding to the current throttle lever, and after the engine speed stabilizes, the step change command is sent again to start the negative step change test of fuel at the current speed.

[0013] The methods for obtaining the preset fuel step amount include:

[0014] Obtain the first relationship graph between physical fuel flow rate Wfm and converted engine speed N2r;

[0015] Based on the first relationship graph, a second relationship graph is obtained between the converted fuel flow rate Wfmr and the converted engine speed N2r; the second relationship graph is fitted to obtain the relationship curve between the converted fuel flow rate Wfmr and the converted engine speed N2r; based on the relationship curve, the fuel flow rate increment value required for the engine speed to increase by a preset amount is obtained through an interpolation calculation model, and the fuel flow rate increment value is used as the preset fuel step amount.

[0016] Preferably, the method for obtaining the preset temperature range of the compressor inlet temperature T2 includes:

[0017] By obtaining the trend diagram of the speed increment caused by a step change in fuel flow rate at each state point under different compressor inlet temperatures through bench testing, the influence coefficient of compressor inlet temperature T2 on speed increment is obtained, and the compressor inlet temperature T2 with an influence coefficient lower than the preset range is taken as the preset temperature range of compressor inlet temperature T2.

[0018] Preferably, the preset temperature range of the compressor inlet temperature T2 is -25℃ to +40℃.

[0019] Preferably, when the converted speed is higher than 88%, the fuel flow increment required for the speed increase to be no less than 0.6% is obtained as the preset fuel step amount.

[0020] Preferably, in the fuel step test, when the converted speed reaches the state point of 76% to 92%, tests are conducted with the compressor guide vane angle A2 locked and unlocked respectively.

[0021] Preferably, the converted fuel flow rate Wfmr is calculated using the following formula:

[0022]

[0023] P2 is the compressor inlet.

[0024] Preferably, the value of the preset increase in rotational speed is less than 2%.

[0025] Preferably, the preset value for increasing the rotational speed is 1%.

[0026] The advantages of this application include: the ability to design experiments through simulation calculations, which ensures the safety of the test run and the validity of the identification data.

[0027] The obtained experimental data can be used to obtain accurate engine time constants and gain coefficients through identification methods, which can be used to further carry out forward design work such as closed-loop parameter design of the control system and stability domain analysis. Attached Figure Description

[0028] Figure 1 A graph showing the relationship between fuel flow rate and converted engine speed;

[0029] Figure 2 Curve showing the effect of T2 temperature on rotational speed

[0030] Figure 3 The effect of temperature T2 on speed increment (step increase) graph

[0031] Figure 4 The effect of temperature T2 on speed increment (decreasing step) graph

[0032] Figure 5 Schematic diagram of the test method. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0034] A test method for identifying engine dynamic characteristic parameters includes:

[0035] The test was conducted with the compressor inlet temperature T2 within the preset temperature range. The engine throttle lever was adjusted to bring the engine to the step point speed, and the fuel step test was started.

[0036] Once the parameters stabilize, a step command for a preset fuel step amount is sent to the engine via the host computer.

[0037] After each step change in the engine speed and the parameters stabilize, the command issued by the host computer is canceled, the engine speed is restored to the state corresponding to the current throttle lever, and after the engine speed stabilizes, the step change command is sent again to start the negative step change test of fuel at the current speed.

[0038] The methods for obtaining the preset fuel step amount include:

[0039] Obtain the first relationship graph between physical fuel flow rate Wfm and converted engine speed N2r;

[0040] Based on the first relationship graph, a second relationship graph is obtained between the converted fuel flow rate Wfmr and the converted engine speed N2r; the second relationship graph is fitted to obtain the relationship curve between the converted fuel flow rate Wfmr and the converted engine speed N2r; based on the relationship curve, the fuel flow rate increment value required for the engine speed to increase by a preset amount is obtained through an interpolation calculation model, and the fuel flow rate increment value is used as the preset fuel step amount.

[0041] The specific implementation method is as follows:

[0042] It is necessary to provide step values ​​for fuel flow at different conversion speeds, ensuring that the speed increase is around 1% and does not exceed 2% under these fuel flow step values. Simultaneously, the speed must not exceed 100% to avoid triggering the over-rev protection logic. First, analyze the engine steady-state data to obtain the correspondence between fuel flow and steady-state speed. Based on this, further analysis is conducted to determine the required fuel flow step amplitude at different conversion speeds. The conversion formula for fuel flow is as follows:

[0043]

[0044] The data were plotted, showing the curves for physical fuel flow rate Wfm and converted engine speed N2r, as well as the curves for converted fuel flow rate Wfmr and converted engine speed N2r. The Wfmr-N2r curve was fitted to obtain a third curve. See the detailed results below. Figure 1 .

[0045] The required fuel flow step amplitude for the test is obtained by calculating the corresponding Wfmr_x value, which is generated by a small increment of about 1% in N2r_y.

[0046] Based on the data analysis results Wfmr_x and N2r_y, an interpolation calculation model is established to analyze the fuel flow increment required for a 1% increase in the current engine speed. At this point, the compressor guide vane angle A2 adjusts with the engine speed; therefore, the analyzed data can be considered to include this characteristic, and no further analysis of the influence of A2 is necessary.

[0047] The following technical points need to be considered during the calculation:

[0048] 1) The fuel flow increment required for the upper and lower steps may be different. In actual test runs, the same amplitude needs to be set at the same speed. Therefore, it is necessary to estimate the speed deviation caused by the same amplitude for the upper and lower steps.

[0049] 2) When the converted speed is higher than 88%, the fuel flow step amplitude is relatively large. The higher the speed, the greater the increase in fuel flow required for the same speed step. At this time, the fuel flow step amplitude can be appropriately reduced. In this invention, different fuel flow step values ​​were used in a certain engine. The speed step generated by changing different fuel flow rates was still not less than 0.6%, which can ensure the identification requirements. When the fuel flow is lower than 150 kg / h at high speed, the simulation results show that the speed increase is 0.5%. Considering factors such as measurement error, a step amplitude of 200 kg / h is used. In actual test runs, it can be adjusted according to the actual speed deviation.

[0050] Preferably, the method for obtaining the preset temperature range of the compressor inlet temperature T2 includes:

[0051] By obtaining the trend diagram of the speed increment caused by a step change in fuel flow rate at each state point under different compressor inlet temperatures through bench testing, the influence coefficient of compressor inlet temperature T2 on speed increment is obtained, and the compressor inlet temperature T2 with an influence coefficient lower than the preset range is taken as the preset temperature range of compressor inlet temperature T2.

[0052] The specific embodiments described above are as follows:

[0053] Analysis of the impact of compressor inlet temperature T2 variation

[0054] Considering the environmental differences in T2 between -25℃ and +40℃, the error in speed increment that might result from setting the engine speed based on physical fuel flow rate is analyzed. During bench testing, T2 showed a decrease at high speeds, dropping by approximately 1 degree Celsius. The trend of steady-state speed variation under different T2 temperatures is shown in [Figure showing the trend]. Figure 2 The trend of speed increment (increase) caused by a step change in fuel flow rate at different state points under different temperatures is shown in the figure. Figure 3 The trend of speed increment (decreasing) caused by a step change in fuel flow rate at different state points under different temperatures is shown in the figure. Figure 4 .

[0055] from Figure 2 It can be seen that as the temperature T2 increases, the engine speed generated by the same fuel flow will decrease, and the impact is greater at lower engine speeds. Since the state point during the experiment was based on the converted engine speed as the steady state point for open-loop control of fuel flow, the influence of absolute values ​​is not important; the focus should be on the impact of the same fuel flow step on the engine speed increment.

[0056] Figure 3 and Figure 4 It can be seen that at low speeds, the change in T2 temperature has a significant and drastic impact on the speed increment. As the speed increases, the impact of T2 temperature changes tends to decrease. At high speeds, the higher the T2 temperature, the smaller the magnitude of the speed increment tends to be. At 98% of the speed, the effect of different T2 temperatures (-25℃ to +40℃) on the speed increment is less than 0.2%.

[0057] Based on the simulation analysis results, the following conclusions can be drawn:

[0058] Physical flow rate can be used as the given value for the step amplitude.

[0059] The effect of T2 temperature changing from -25℃ to +40℃ on the speed increment is acceptable, with a greater impact at low speeds and a smaller impact at high speeds.

[0060] At 98% speed, the higher the T2 temperature, the smaller the speed increase. The speed increase caused by the change from -25℃ to +40℃ is reduced by 0.2%, which is beneficial to engine stability and prevents over-revving.

[0061] Furthermore, consider the impact of A2 on engine speed: During the test, A2 changes with engine speed when controlling speed in a closed-loop manner. If a step change in fuel flow is performed with A2 locked, a single fuel input can achieve the required engine speed response. However, when the fuel flow increases in a step, locking A2 is equivalent to the normal operating line A2 angle being deviated, resulting in a lower N2-converted engine speed for the same fuel flow. While there is no risk of exceeding the speed limit, locking A2 may introduce a surge risk. This risk cannot be verified through existing engine models; only risk identification is possible. In other words, locking A2 during an open-loop step change in fuel flow may pose a surge risk, requiring appropriate countermeasures.

[0062] Therefore, the specific experimental method embodiment of this application is as follows: With the engine at idle or above idle speed, after the warm-up process is completed, the throttle lever is adjusted to bring the engine to the step point speed, and the fuel step test begins. After the parameters stabilize, a command is sent via the host computer, and the fuel input is performed in an open-loop step according to the step value sent by the host computer. Each step is maintained for 20 seconds (adjustable as needed). After the parameters stabilize, the command sent by the host computer is canceled. The engine speed is restored to the state corresponding to the current throttle lever. After the engine state stabilizes, the command is sent again to begin the fuel negative step test at the current speed. In n 2r For state points ranging from 76% to 92%, α2 locking and unlocking tests need to be performed separately. That is, α2 locking and unlocking are set via the host computer before the fuel step. For other state points, only α2 unlocking tests are required.

[0063] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A test method for identifying engine dynamic characteristic parameters, characterized in that, include: The test was conducted with the compressor inlet temperature T2 within the preset temperature range. The engine throttle lever was adjusted to bring the engine to the step point speed, and the fuel step test was started. Once the parameters stabilize, a step command for a preset fuel step amount is sent to the engine via the host computer. After each step change in the engine speed and the parameters stabilize, the command issued by the host computer is canceled, the engine speed is restored to the state corresponding to the current throttle lever, and after the engine speed stabilizes, the step change command is sent again to start the negative step change test of fuel at the current speed. The methods for obtaining the preset fuel step amount include: Obtain the first relationship graph between physical fuel flow rate Wfm and converted engine speed N2r; Based on the first relationship graph, a second relationship graph is obtained between the converted fuel flow rate Wfmr and the converted engine speed N2r; the second relationship graph is fitted to obtain the relationship curve between the converted fuel flow rate Wfmr and the converted engine speed N2r; based on the relationship curve, the fuel flow rate increment value required for the engine speed to increase by a preset amount is obtained through an interpolation calculation model; the fuel flow rate increment value is used as the preset fuel step amount. The method for obtaining the preset temperature range of the compressor inlet temperature T2 includes: By obtaining the trend diagram of the speed increment caused by a step change in fuel flow rate at each state point under different compressor inlet temperatures through bench testing, the influence coefficient of compressor inlet temperature T2 on speed increment is obtained, and the compressor inlet temperature T2 with an influence coefficient lower than the preset range is taken as the preset temperature range of compressor inlet temperature T2. The preset temperature range of the compressor inlet temperature T2 is -25℃ to +40℃; When the converted speed is higher than 88%, the fuel flow increment required for the speed to increase by no less than 0.6% is obtained as the preset fuel step amount; In the fuel step test, when the converted speed reaches the state point of 76% to 92%, tests are conducted with the compressor guide vane angle A2 locked and unlocked respectively. The converted fuel flow rate Wfmr is calculated using the following formula: ； P2 is the compressor inlet.

2. The test method for identifying engine dynamic characteristic parameters as described in claim 1, characterized in that, The preset increase in rotational speed is less than 2%.

3. The test method for identifying engine dynamic characteristic parameters as described in claim 1, characterized in that, The preset value for increasing the rotational speed is 1%.

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