Method and system for predicting maximum rotating speed of power turbine after engine loses load

Abstract

The invention relates to a method and system for predicting the maximum rotating speed of a power turbine after an engine loses load, and belongs to the field of aviation gas turboshaft engines. The method comprises the following steps that a pressure signal of a gas compressor outlet of the engine, a pressure signal of a main oil way of a fuel oil distribution device and a pressure signal of an auxiliary oil way of the fuel oil distribution device are obtained; performing a simulation over-rotation test under the maximum state of the engine, and obtaining a fuel oil rule of the maximum state over-rotation of the engine according to a test result; carrying out segmented iterative calculation on the rotating speeds of the power turbine at different time points in the maximum state over-rotating process of the engine to obtain a relationship between the rotating speeds of the power turbine and time; and according to the relationship between the power turbine rotating speed and time, the maximum power turbine rotating speed in the maximum state overrunning process of the engine is obtained. According to the method, the response time, the fuel attenuation rule and the torque change rule of the over-rotation protection system are fully considered, and the maximum rotating speed under the condition of shaft breakage of the engine can be accurately predicted.

Description

Technical Field

[0001] The present invention belongs to the field of aero-gas turbine engines, and particularly relates to a method and system for predicting the maximum speed of a power turbine after an engine loses its load. Background Art

[0002] The fracture of the torque transmission shaft of a turboprop engine is a common form of the power turbine losing its load. At the moment of shaft fracture, since the gas generator continues to generate high-energy gas, it will cause the engine turbine to overspin. In severe cases, the turbine blades or disks may fracture, endangering flight safety. To protect the structural integrity of the turboprop engine and flight safety, the turboprop engine is designed with a power turbine overspin protection system. Due to the existence of a certain response time in the overspin protection system, the maximum value of the actual overspin speed is higher than the overspin protection value.

[0003] When the prior art predicts the maximum speed of the power turbine losing its load, it is assumed that the energy output of the gas generator remains unchanged, and the calculation is carried out according to the relationship between the energy output of the gas turbine, the pneumatic torque, and the relationship between the power turbine speed and acceleration. In fact, after the power turbine loses its load, the overspin protection system will reduce the fuel flow rate, thereby reducing the energy output of the gas generator. The assumption does not match the actual situation and will cause certain errors. The prior art believes that the maximum speed has been reached when the overspin protection system responds. In fact, when the overspin protection system responds, since it takes a certain time for fuel cut-off or reduction, the engine speed will continue to rise during this period. Therefore, this calculation method does not fully consider the fuel attenuation law and there are certain errors. The existing fuel flowmeter is installed in the inlet pipeline of the test bench, and the flow measurement is carried out through a data acquisition system with a low sampling rate (lower than 20Hz). However, this method cannot reflect the real flow rate entering the engine combustion chamber in the transient state. Therefore, this method has errors and hysteresis in the measurement of the fuel flow rate and cannot accurately obtain the real law of the fuel flow rate during fuel cut-off.

[0004] It can be seen from this that it is difficult for the prior art to accurately predict the maximum speed in the case of engine shaft fracture. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for predicting the maximum speed of a power turbine after an engine loses its load, including the following steps:

[0006] Obtain the pressure signal at the outlet of the compressor of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device;

[0007] Conduct a simulated overspin test under the maximum state of the engine, and obtain the fuel law of the engine overspinning under the maximum state according to the test results;

[0008] Perform piecewise iterative calculations on the power turbine speed at different time points during the over-speed process of the engine at maximum state to obtain the relationship between the power turbine speed and time;

[0009] Based on the relationship between the power turbine speed and time, obtain the maximum power turbine speed during the over-speed process of the engine at maximum state.

[0010] Furthermore, the simulated over-speed test includes the following steps:

[0011] Start the engine and run it to the maximum state; the running time is 3 - 5 minutes;

[0012] Use the test bench test equipment to control the over-speed drain valve of the fuel distribution device to be turned on until the fuel of the engine is completely cut off;

[0013] Use the test bench test equipment to obtain the variation laws of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil circuit of the fuel distribution device, and the pressure signal of the secondary oil circuit of the fuel distribution device during the over-speed of the engine at maximum state with the fuel cut-off time;

[0014] According to the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil circuit of the fuel distribution device, and the pressure signal of the secondary oil circuit of the fuel distribution device, calculate the fuel flow rates of the main oil circuit and the secondary oil circuit of the fuel distribution device to obtain the over-speed fuel law.

[0015] Furthermore, the variation laws of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil circuit of the fuel distribution device, and the pressure signal of the secondary oil circuit of the fuel distribution device during the over-speed of the engine at maximum state are expressed as:

[0016] P fz = f1(t), P ff = f2(t), P s3 = f3(t)

[0017] In the formula, P fz is the pressure signal of the main oil circuit of the fuel distribution device; P ff is the pressure signal of the secondary oil circuit of the fuel distribution device; P s3 is the pressure signal at the compressor outlet of the engine.

[0018] Furthermore, the calculation formula of the over-speed fuel law is expressed as:

[0019]

[0020] W f = W fz + W ff = f4(t)

[0021] In the formula, Wfz is the main oil circuit fuel flow rate of the fuel distribution device, W ff is the secondary oil circuit fuel flow rate of the fuel distribution device, W f is the total fuel flow rate flowing into the engine combustion chamber, b is the main oil circuit flow coefficient, d is the secondary oil circuit flow coefficient, and c is the correction coefficient.

[0022] Further, the relational expression of the power turbine speed and time is expressed as:

[0023] N p = f6(t).

[0024] Further, the calculation formula for performing piecewise iterative calculation on the power turbine speed at different time points during the engine maximum state overrun process is expressed as:

[0025] Np x+1 = Np x + a x * T0 / n

[0026] In the formula, a is the power turbine rotor acceleration; T0 is the total duration of the overrun process; n is the number of segments of the total duration of the overrun process.

[0027] Further, the calculation formula for the power turbine rotor acceleration is expressed as:

[0028]

[0029] In the formula, T is the aerodynamic torque of the dynamic process; k1 is the moment of inertia of the power turbine rotor system; N p is the power turbine speed.

[0030] Further, the calculation formula for the aerodynamic torque of the dynamic process is expressed as:

[0031]

[0032] In the formula, N p is the power turbine speed; Pdn is the engine equivalent power.

[0033] Further, the calculation formula for the engine equivalent power is expressed as:

[0034] Pdn = f(W f , N p ) = f5(t)

[0035] In the formula, W f is the total fuel flow rate flowing into the engine combustion chamber; N p is the power turbine speed.

[0036] A maximum speed prediction system for a power turbine after an engine loses its load, comprising:

[0037] An acquisition module: used to collect the pressure signal at the compressor outlet of the engine, the pressure signal of the main fuel oil path of the fuel distribution device, and the pressure signal of the secondary fuel oil path of the fuel distribution device;

[0038] A test module: used to conduct a simulated over-speed test under the maximum condition of the engine, and obtain the fuel law of the engine over-speed under the maximum condition according to the test results;

[0039] A calculation module: perform piecewise iterative calculation on the power turbine speed at different time points during the engine over-speed process under the maximum condition, and obtain the relationship between the power turbine speed and time;

[0040] A turbine speed module: obtain the maximum power turbine speed during the engine over-speed process under the maximum condition according to the relationship between the power turbine speed and time.

[0041] Compared with the prior art, the beneficial effects of the present invention are:

[0042] 1) The present invention fully considers the response time of the over-speed protection system, the fuel attenuation law, and the torque change law, and can accurately predict the maximum speed in the case of engine shaft breakage.

[0043] 2) The present invention uses the test bench test equipment to obtain the variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main fuel oil path of the fuel distribution device, and the pressure signal of the secondary fuel oil path of the fuel distribution device during the engine over-speed under the maximum condition with respect to the fuel cut-off time, thus fully considering the response time of the over-speed protection system.

[0044] 3) The present invention performs piecewise iterative calculation on the power turbine speed at different time points during the engine over-speed process under the maximum condition, obtains the relationship between the power turbine speed and time, and thus obtains the maximum power turbine speed during the engine over-speed process under the maximum condition, thus considering the torque change law.

[0045] 4) The present invention conducts a simulated over-speed test under the maximum condition of the engine, and obtains the fuel law of the engine over-speed under the maximum condition according to the test results, thus considering the fuel attenuation law.

[0046] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will become obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures pointed out in the specification and the drawings. Description of the Drawings

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0048] Figure 1 Shows the flowchart of the method for predicting the maximum speed of the power turbine after the engine of the present invention loses its load;

[0049] Figure 2 Shows a schematic diagram of the variation law of the pressure signal at the compressor outlet of the engine with maximum state overrun, the pressure signal of the main oil circuit of the fuel distribution device, and the pressure signal of the secondary oil circuit of the fuel distribution device with the fuel cut-off time;

[0050] Figure 3 Shows a schematic diagram of the overrun fuel law;

[0051] Figure 4 Shows a schematic diagram of the variation law of the equivalent power of the engine;

[0052] Figure 5 Shows a schematic diagram of the relationship between the power turbine speed and time;

[0053] Figure 6 Shows a schematic diagram of the principle of the fuel distribution device and the test bench test equipment;

[0054] Figure 7 Shows the block diagram of the system for predicting the maximum speed of the power turbine after the engine of the present invention loses its load. Detailed implementation manners

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0056] Embodiment 1

[0057] Figure 1 Shows the flowchart of the method for predicting the maximum speed of the power turbine after the engine of the present invention loses its load. As Figure 1 shown, a method for predicting the maximum speed of the power turbine after the engine loses its load includes the following steps:

[0058] Obtain the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device;

[0059] Conduct a simulated over-speed test under the maximum engine condition, and obtain the fuel law for engine over-speed under the maximum condition according to the test results;

[0060] Perform piecewise iterative calculations on the power turbine speed at different time points during the engine over-speed process under the maximum condition to obtain the relationship between the power turbine speed and time;

[0061] Based on the relationship between the power turbine speed and time, obtain the maximum power turbine speed during the engine over-speed process under the maximum condition.

[0062] In some embodiments, the set conditions for performing piecewise iterative calculations on the power turbine speed at different time points during the engine over-speed process under the maximum condition are as follows:

[0063] During the over-speed process, a steady-state analysis method is used for the transient analysis of the aerodynamic torque of the power turbine;

[0064] During the over-speed process, the power turbine speed constant system with a slower response time has no influence on the fuel attenuation law.

[0065] Specifically, the power turbine speed constant system with a slower response time refers to controlling the fuel by adjusting the needle valve opening of the fuel pump regulator, so the response time is slower.

[0066] In some embodiments, the simulated over-speed test includes the following steps:

[0067] Start the engine and run it to the maximum condition; the running time is 3 - 5 minutes;

[0068] Use the test bench test equipment to control the opening of the over-speed drain valve of the fuel distribution device until the fuel supply to the engine is completely cut off;

[0069] Use the test bench test equipment to obtain the variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device during the engine over-speed process under the maximum condition with respect to the fuel cut-off time;

[0070] According to the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device, calculate the fuel flow rates of the main oil path and the secondary oil path of the fuel distribution device to obtain the over-speed fuel law.

[0071] In some embodiments, the judgment criterion for complete fuel cut-off of the engine is that both the pressure signal of the main oil path of the fuel distribution device and the pressure signal of the secondary oil path of the fuel distribution device are less than the pressure signal at the compressor outlet of the engine.

[0072] Figure 2 The schematic diagram shows the variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device with the fuel cut-off time during the engine's maximum state over-speed. As Figure 2 shown, in some embodiments, the variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device with the fuel cut-off time is expressed as:

[0073] P fz = f1(t), P ff = f2(t), P s3 = f3(t)

[0074] Wherein, P fz is the pressure signal of the main oil path of the fuel distribution device; P ff is the pressure signal of the secondary oil path of the fuel distribution device; P s3 is the pressure signal at the compressor outlet of the engine.

[0075] Figure 3 The schematic diagram shows the over-speed fuel law. As Figure 3 shown, in some embodiments, the calculation formula of the over-speed fuel law is expressed as:

[0076]

[0077] W f = W fz + W ff = f4(t)

[0078] Wherein, W fz is the fuel flow rate of the main oil path of the fuel distribution device, W ff is the fuel flow rate of the secondary oil path of the fuel distribution device, W f is the total fuel flow rate flowing into the engine combustion chamber, b is the main oil path flow coefficient, d is the secondary oil path flow coefficient, and c is the correction coefficient.

[0079] Figure 5 The schematic diagram shows the relationship between the power turbine speed and time. As Figure 5 shown, in some embodiments, the relational expression between the power turbine speed and time is expressed as:

[0080] N p = f6(t).

[0081] In some embodiments, the calculation formula for the piecewise iterative calculation of the power turbine speed at different time points during the engine's maximum state over-speed process is expressed as:

[0082] Np x+1 = Np x + a x * T0 / n

[0083] In the formula, a is the acceleration of the power turbine rotor; T0 is the total duration of the supercharging process; n is the number of segments of the total duration of the supercharging process.

[0084] Specifically, after the total fuel flow rate into the engine combustion chamber becomes zero, the gas generator of the engine no longer outputs energy. Therefore, the time from the start to W f = 0 is set as the total duration T0, that is, the total duration of the supercharging process is T0. The supercharging process T0 is divided into n segments, and the calculation is carried out in segments with T0 / n as one segment. The acceleration of the power turbine rotor obtained after the initial parameters of each segment of time participate in the calculation is regarded as the average acceleration of this segment. The power turbine speed of each segment is equal to the power turbine speed of the previous segment plus the acceleration of the power turbine rotor multiplied by the time. That is, the power turbine speed of the x-th segment is expressed as:

[0085] Np x+1 = Np x + a x * T0 / n

[0086] Thus, the relationship between the power turbine speed and time N p = f6(t) is obtained, and the maximum power turbine speed during the supercharging process is obtained.

[0087] In some embodiments, the segmented iterative calculation process of the power turbine speed includes the initial value of the power turbine speed. The calculation formula for the initial value of the power turbine speed is expressed as:

[0088] Np1 = Np0 + a1 * T0 / n

[0089] In some embodiments, the calculation formula for the acceleration of the power turbine rotor is expressed as:

[0090]

[0091] In the formula, T is the aerodynamic torque during the dynamic process; k1 is the moment of inertia of the power turbine rotor system; N p is the power turbine speed.

[0092] In some embodiments, the calculation formula for the aerodynamic torque during the dynamic process is expressed as:

[0093]

[0094] In the formula, N p is the power turbine speed; Pdn is the equivalent power of the engine.

[0095] Figure 4 shows a schematic diagram of the variation law of the engine equivalent power. As Figure 4 shown, in some embodiments, the calculation formula of the engine equivalent power is expressed as:

[0096] Pdn = f(W f , N p ) = f5(t)

[0097] wherein, W f is the total fuel flow rate into the engine combustion chamber; N p is the power turbine speed.

[0098] Specifically, an engine performance model is established according to the component-level model building method of a turboshaft engine, that is, the common working equations are established based on the characteristics of each engine component, the inlet and outlet conditions and the balance conditions, and the steady-state performance of the engine at the maximum state is obtained by iterative solution. On this basis, the transient state is simulated, and the fuel supply is adjusted according to W f = f4(t) to obtain the relationship between the engine equivalent power Pdn and time.

[0099] Specifically, the fuel supply adjustment is to input the fuel flow rate into the engine performance model, and the engine performance model calculates to obtain the engine equivalent power.

[0100] Specifically, the component-level modeling object is a single-rotor turboshaft engine with a free turbine. The engine is divided into multiple sub-components for calculation, and the common working equations are established through the pneumatic and thermodynamic relationships between the components. The engine performance is calculated according to the obtained common working point. This is the prior art, so it will not be elaborated here.

[0101] Specifically, since the power turbine characteristic diagram is used when establishing the engine performance model, and the power turbine characteristic diagram contains the power turbine efficiency at different power turbine speeds, the power turbine efficiency, the blade air flow friction force, the disk aerodynamic drag, and the bearing friction force are all considered when calculating the output power at different power turbine speeds in the component-level model, and no separate calculation is performed. The power turbine efficiency here has considered the blade air flow friction force, the disk aerodynamic drag, and the bearing friction force.

[0102] In some embodiments, an engine model is established according to the general component-level model building method of a turboshaft engine, and the engine equivalent power is calculated according to the total fuel flow rate into the engine combustion chamber and the power turbine speed.

[0103] Figure 6 shows a schematic diagram of the principle of the fuel distribution device and the test bench test equipment. As Figure 6As shown, specifically, the test stand test equipment includes a high-speed dynamic recorder, a first pressure sensor, a second pressure sensor, and a third pressure sensor. The electrical system of the high-speed dynamic recorder is electrically connected to the overspeed cut-off solenoid valve of the fuel distribution device. A first pressure sensor is provided at the valve of the main oil path of the fuel distribution device, a second pressure sensor is provided at the valve of the sub-oil path of the fuel distribution device, and a third pressure sensor is provided at the outlet of the compressor. The first pressure sensor, the second pressure sensor, and the third pressure sensor are all electrically connected to the high-speed dynamic recorder, so as to transmit the pressure signals of the main oil path, the sub-oil path, and the compressor outlet to the high-speed dynamic recorder.

[0104] Specifically, the sampling rate of the high-speed dynamic recorder ≥ 1000 Hz.

[0105] Figure 7 The block diagram of the maximum power turbine speed prediction system of the engine of the present invention after losing load is shown. As Figure 7 shown, a maximum power turbine speed prediction system after the engine loses load includes:

[0106] An acquisition module: used to collect the pressure signal at the outlet of the compressor of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the sub-oil path of the fuel distribution device;

[0107] A test module: used to conduct a simulated overspeed test under the maximum state of the engine, and obtain the fuel law of the engine's maximum state overspeed according to the test results;

[0108] A calculation module: perform piecewise iterative calculation on the power turbine speed at different time points during the engine's maximum state overspeed process to obtain the relationship between the power turbine speed and time;

[0109] A turbine speed module: obtain the maximum power turbine speed during the engine's maximum state overspeed process according to the relationship between the power turbine speed and time.

[0110] Embodiment 2

[0111] On the basis of Embodiment 1, the overspeed process is divided into n segments, and the subscripts 1, 2, 3... n represent the starting parameters of each segment. N p0 is the overspeed response speed of the engine power turbine. Then the calculation process of the relationship between the power turbine speed and time is expressed as:

[0112] Pdn1 = f(W f1 , N p0 ) = f(P fz1 , P ff1 , P s3-1 , N p0 )

[0113]

[0114] Np1 = N p0 + a1 * T0 / n

[0115] Pdn2 = f(W f2 , N p1 ) = f(P fz2 , P ff2 , P s3-2 , N p1 )

[0116]

[0117] Np2 = Np1 + a2 * T0 / n

[0118] ……

[0119] Pdn n = f(W fn , N pn-1 ) = f(P fz n , P ff n , P s3-n , N pn-1 )

[0120]

[0121] Np n = N pn-1 + a n * T0 / n

[0122] Specifically, 0 - 10 ms is the first stage, 10 ms - 20 ms is the second stage. According to the parameters at 0 ms, the calculated acceleration is 30 revolutions / ms. It is considered that the power turbine speed has increased by 300 revolutions after 10 ms in the first stage.

[0123] Specifically, N p0 is the over - speed response speed of the engine power turbine, which is the power turbine speed in the first embodiment.

[0124] Test:

[0125] The power turbine no - load speed calculation under the maximum condition of the turboshaft engine was carried out, and the maximum speed prediction table in the case of engine shaft breakage was obtained. See Table 1.

[0126]

[0127] Table 1

[0128] It can be seen from Table 1 that the maximum power turbine speed during the over - speed process is predicted to be 127.52%, accurately predicting the maximum speed in the case of engine shaft breakage.

[0129] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the maximum speed of a power turbine after an engine loses its load, characterized in that, It includes the following steps: Obtain the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device; Conduct a simulated over-speed test under the maximum engine condition, and obtain the fuel law for engine over-speed under the maximum condition according to the test results; Perform piecewise iterative calculations on the power turbine speed at different time points during the engine over-speed process under the maximum condition to obtain the relationship between the power turbine speed and time; Based on the relationship between the power turbine speed and time, obtain the maximum power turbine speed during the engine over-speed process under the maximum condition.

2. The method for predicting the maximum speed of the power turbine after the engine loses its load according to claim 1, wherein The simulated over-speed test includes the following steps: Start the engine and run it to the maximum condition; the running time is 3 - 5 minutes; Use the test bench test equipment to control the opening of the over-speed drain valve of the fuel distribution device until the fuel supply to the engine is completely cut off; Use the test bench test equipment to obtain the variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device with the fuel cut-off time during the engine over-speed process under the maximum condition; Based on the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device, calculate the fuel flow rates of the main oil path and the secondary oil path of the fuel distribution device to obtain the over-speed fuel law.

3. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 2, wherein The variation law of the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device with the fuel cut-off time during the engine over-speed process under the maximum condition is expressed as: P fz = f1(t), P ff = f2(t), P s3 = f3(t) Wherein, P fz is the pressure signal of the main oil path of the fuel distribution device; P ff is the pressure signal of the secondary oil path of the fuel distribution device; P s3 is the pressure signal at the outlet of the compressor of the engine.

4. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 3, characterized in that, The calculation formula of the over-speed fuel law is expressed as: W f = W fz + W ff = f4(t) Wherein, W fz is the fuel flow rate of the main oil path of the fuel distribution device, W ff is the fuel flow rate of the secondary oil path of the fuel distribution device, W f is the total fuel flow rate flowing into the engine combustion chamber, b is the main oil path flow coefficient, d is the secondary oil path flow coefficient, and c is the correction coefficient.

5. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 2, characterized in that, The relational expression between the power turbine speed and time is expressed as: N p = f6(t).

6. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 2, characterized in that, The calculation formula for performing piecewise iterative calculations on the power turbine speed at different time points during the engine over-speed process under the maximum condition is expressed as: Np x+1 = Np x + a x * T0 / n In the formula, a is the acceleration of the power turbine rotor; T0 is the total duration of the over-speed process; n is the number of segments of the total duration of the over-speed process.

7. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 5, characterized in that, The calculation formula of the acceleration of the power turbine rotor is expressed as: Where T is the pneumatic torque of the dynamic process; k1 is the moment of inertia of the power turbine rotor system; N p is the rotational speed of the power turbine.

8. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 7, characterized in that, The calculation formula of the aerodynamic torque in the dynamic process is expressed as: Where N p is the rotational speed of the power turbine; Pdn is the equivalent power of the engine.

9. The method for predicting the maximum speed of a power turbine after an engine loses its load according to claim 8, wherein The calculation formula of the equivalent power of the engine is expressed as: Pdn = f(W f , N p ) = f5(t) Where, W f is the total fuel flow rate into the engine combustion chamber; N p is the power turbine speed.

10. A maximum speed prediction system for a power turbine after an engine loses its load, characterized in that, It includes: An acquisition module: used to collect the pressure signal at the compressor outlet of the engine, the pressure signal of the main oil path of the fuel distribution device, and the pressure signal of the secondary oil path of the fuel distribution device; A test module: used to conduct a simulated over-speed test under the maximum engine condition and obtain the fuel law for engine over-speed under the maximum condition according to the test results; A calculation module: perform piecewise iterative calculations on the power turbine speed at different time points during the engine over-speed process under the maximum condition to obtain the relationship between the power turbine speed and time; A turbine speed module: based on the relationship between the power turbine speed and time, obtain the maximum power turbine speed during the engine over-speed process under the maximum condition.

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