A method for starting a turbofan engine with back side wind

Abstract

This application belongs to the field of turbofan engine starting design technology, specifically involving a turbofan engine backwind starting method, including: Step 1, identifying whether the turbofan engine is starting under high-speed backwind conditions by whether the low-pressure rotor reverses; if the low-pressure rotor reverses, the turbofan engine is identified as starting under high-speed backwind conditions; Step 2, after identifying that the turbofan engine is starting under high-speed backwind conditions, determining the wind pressure resistance PdX of the turbofan engine starting under high-speed backwind conditions by the low-pressure rotor reverse rotation speed and the correspondence between the low-pressure rotor reverse rotation speed and wind pressure resistance; Step 3, after the low-pressure rotor changes from reverse rotation to forward rotation under the starter motor, reducing the nozzle throat area A8, adjusting the nozzle exit area A9 and vector angle δA9 to shield the nozzle throat, increasing the ignition speed to ignite the turbofan engine, and increasing the fuel supply speed to supply fuel to the turbofan engine, thereby starting the turbofan engine.

Description

Technical Field

[0001] This application belongs to the field of turbofan engine starting design technology, specifically relating to a turbofan engine back-side wind starting method. Background Technology

[0002] The starting performance design of turbofan engines needs to take into account the impact of atmospheric wind conditions on starting performance.

[0003] The atmospheric wind environment during turbofan engine startup, such as Figure 1 As shown, in the atmospheric wind environment of Region 1, the wind direction is towards the front of the engine, generating a large positive wind pressure on the engine. This results in a higher starter rotation speed, improved combustion chamber operating conditions, and increased turbine pressure drop, making it easier to start the turbofan engine. In the atmospheric wind environments of Regions 2 and 4, the wind direction is to the side of the engine, and the wind pressure component along the engine axis is relatively small, having little impact on the starting of the turbofan engine. However, in the atmospheric wind environment of Region 3, the wind direction is towards the rear of the engine, generating significant wind pressure drag on the engine. This leads to a decrease in engine intake airflow, an increase in exhaust resistance, a decrease in turbine pressure ratio, and an increase in fan pressure ratio and power. At the same time, the combustion chamber ignition environment deteriorates, making it difficult to start the turbofan engine and severely affecting its normal starting, resulting in start-up failure.

[0004] Considering the impact of atmospheric wind conditions on the starting performance of turbofan engines, the starting performance of turbofan engines is designed, primarily focusing on starting under high-speed backwind conditions. When starting a turbofan engine under high-speed backwind conditions, the high wind pressure resistance can cause abnormal airflow within the engine's flow channels, resulting in slow speed increase, ignition delay, and ignition knocking. Research experience shows that ignition is the main weak point in backwind starting of turbofan engines, and reliable ignition is a key factor affecting the success rate of backwind starting.

[0005] Currently, most mainstream technical solutions are designed to start turbofan engines by increasing the ignition speed and fuel injection speed, based on the identification of backwind starting conditions. However, this approach only identifies the backwind starting condition and does not consider the magnitude of wind pressure resistance. Increasing the ignition speed and fuel injection speed relies on increasing the starter motor power. To ensure successful turbofan engine starting, a high-power starter motor needs to be designed. The design of a high-power starter motor requires a long development cycle and substantial funding. Furthermore, it is limited by installation space and compatibility with aircraft and ground equipment, making the solution impractical and unable to effectively solve the problem of backwind starting of turbofan engines.

[0006] This application is made in view of the aforementioned technical deficiencies. Summary of the Invention

[0007] The purpose of this application is to provide a method for starting a turbofan engine with back side wind, so as to overcome or mitigate at least one of the known technical defects.

[0008] The technical solution of this application is:

[0009] A method for starting a turbofan engine with back-side wind includes:

[0010] Step 1: Identify whether the turbofan engine is starting under high-speed back wind conditions by checking whether the low-pressure rotor is rotating in reverse.

[0011] If the low-pressure rotor reverses, it indicates that the turbofan engine is starting under high-speed back wind conditions;

[0012] Step 2: After identifying that the turbofan engine is started under high-speed back crosswind conditions, determine the wind pressure resistance PdX of the turbofan engine when starting under high-speed back crosswind conditions by reversing the low-pressure rotor speed and based on the correspondence between the low-pressure rotor speed and wind pressure resistance.

[0013] Step 3: After the low-pressure rotor changes from reverse rotation to forward rotation under the starter drive, reduce the nozzle throat area A8, adjust the nozzle exit area A9 and vector angle δA9 to shield the nozzle throat, increase the ignition speed to ignite the turbofan engine, increase the fuel supply speed to supply fuel to the turbofan engine, and start the turbofan engine.

[0014] After the turbofan engine is successfully ignited and Pt6≥Pt6.st+C, the nozzle throat area A8 and the exit area A9 are adjusted to their maximum values, and the vector angle δA9 is 0º.

[0015] Pt6 is the real-time total turbine exhaust pressure of the turbofan engine;

[0016] Pt6.st is the total turbine exhaust pressure at the start of the turbofan engine;

[0017] C is an adjustable parameter greater than 0.

[0018] According to at least one embodiment of this application, in the above-described turbofan engine back-side wind starting method, in step two, the correspondence between the low-pressure rotor reversal speed and the wind pressure resistance is established based on simulation or experimental results.

[0019] According to at least one embodiment of this application, in the above-described turbofan engine back-side wind starting method, in step three, the adjustment parameter C is set to 1.5 PdX.

[0020] According to at least one embodiment of this application, in the above-described turbofan engine back-side wind starting method, in step three, the timing for igniting and supplying fuel to the turbofan engine is when Pt6 ≥ Pt6.st + ΔPst and Pt6 ≥ Pt6.st + PdX, wherein...

[0021] ΔPst is the difference between the total pressure at the fan inlet and the total pressure at the turbine exhaust at the start of the turbofan engine.

[0022] According to at least one embodiment of this application, in the above-described turbofan engine back-side wind starting method, in step three, the timing for igniting and supplying fuel to the turbofan engine is when Pt6 ≥ Pt6.st + ΔPst or n2R ≥ f(ΔPst), wherein...

[0023] n2R is the real-time high-pressure rotor relative conversion speed of the turbofan engine.

[0024] f(ΔPst) is the difference between the total pressure at the fan inlet and the total pressure at the turbine exhaust at the start of the turbofan engine, corresponding to the relative conversion speed of the high-pressure rotor.

[0025] This application has at least the following beneficial technical effects:

[0026] This invention provides a method for starting a turbofan engine under backwind conditions. The design effectively identifies whether the turbofan engine is starting under high-speed backwind conditions by checking if the low-pressure rotor is reversing. It also determines the wind pressure resistance during high-speed backwind starting based on the low-pressure rotor's reversal speed. Furthermore, by adjusting the nozzle throat area and ignition / fuel injection speeds during the starting process, the internal flow pressure during ignition is increased to counteract the backwind starting wind pressure resistance. Additionally, by adjusting the nozzle exit area and vector angle, the throat area is shielded, reducing the wind pressure resistance during backwind starting at its source. This method effectively solves the ignition delay and detonation problems that occur when starting a turbofan engine under high wind speeds, achieving reliable starting of the turbofan engine. It is simple to implement on vector thrust engines, easy to improve, and widely adaptable, significantly saving time, manpower, and economic costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the atmospheric wind environment during turbofan engine startup;

[0028] Figure 2 This is a schematic diagram of the turbofan engine back-side wind starting method provided in the embodiments of this application;

[0029] Figure 3 This is a schematic diagram showing that the nozzle exit area A9 and throat area A8 are at their maximum values ​​and the vector angle is 0º, according to an embodiment of this application.

[0030] Figure 4This is a schematic diagram of adjusting the nozzle exit area A9 and the vector angle δA9 to block the nozzle throat, as provided in the embodiments of this application.

[0031] Figure 5 The embodiments of this application provide the nozzle throat area A8, exit area A9, and vector angle during the turbofan engine start-up process. A schematic diagram of the control law.

[0032] To better illustrate this embodiment, some content in the accompanying drawings may be omitted, enlarged, or reduced. They are for illustrative purposes only and should not be construed as limiting the scope of this application. Detailed Implementation

[0033] To make the technical solution and advantages of this application clearer, the technical solution of this application will be described in a clearer and more complete manner below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some embodiments of this application, and are only used to explain this application, not to limit this application. It should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings, and other related parts can be referred to the general design.

[0034] Furthermore, unless otherwise defined, the technical or scientific terms used in this application description shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The word "comprising" as used in this application description indicates that the concept preceding the word encompasses the concepts listed following the word and their equivalents, without excluding other related concepts.

[0035] This application, starting from the requirements of turbofan engine back-side wind starting capability, comprehensively considers factors such as turbofan engine bleed air and power extraction, starter power and torque distribution, and starting time requirements, and provides a turbofan engine back-side wind starting method, such as... Figure 2 As shown.

[0036] Step 1: Identify whether the turbofan engine is started under high-speed leeward wind conditions.

[0037] Due to the influence of strong winds from the back side, the low-pressure rotor of the turbofan engine will reverse at the start of startup. After being turned by the starter motor, the speed will drop from reverse to 0 and then begin to rotate in the forward direction.

[0038] Therefore, before starting a turbofan engine, it can be determined whether the turbofan engine is starting under high-speed back wind conditions by checking whether the low-pressure rotor is reversing. If the low-pressure rotor is reversing, the turbofan engine is starting under high-speed back wind conditions. If the low-pressure rotor is not reversing, the turbofan engine is not starting under high-speed back wind conditions. In this case, the turbofan engine can be started using conventional methods.

[0039] Step 2: Determine the wind pressure drag PdX of the turbofan engine starting under high-speed back wind conditions.

[0040] Before a turbofan engine starts, the reverse rotation speed of the low-pressure rotor can reflect the magnitude of wind pressure resistance to a certain extent, that is, the wind pressure of the high-speed back wind along the engine axis component.

[0041] Therefore, based on simulation or experimental results, a correspondence between the low-pressure rotor reversal speed (n1fz1, n1fz2...n1fzN) and the wind pressure resistance (PdX1, PdX2...PdXN) can be established. After identifying that the turbofan engine starts under high-speed back wind conditions, the wind pressure resistance PdX of the turbofan engine starting under high-speed back wind conditions can be determined by using the low-pressure rotor reversal speed and the correspondence between the low-pressure rotor reversal speed and the wind pressure resistance.

[0042] Step 3: Reduce the nozzle throat area A8, adjust the nozzle exit area A9 and vector angle δA9, shield the nozzle throat, increase the ignition speed to ignite the turbofan engine, increase the fuel supply speed to supply fuel to the turbofan engine, and start the turbofan engine.

[0043] In order to effectively increase the internal flow path pressure of the turbofan engine, so that the exhaust can overcome the wind pressure resistance and be discharged outside the engine during turbofan engine start-up, after the low-pressure rotor is turned from reverse rotation to forward rotation by the starter, the nozzle throat area is appropriately reduced for a short time to increase the ignition speed for turbofan engine ignition and increase the fuel supply speed for turbofan engine fuel supply. This can counteract the wind pressure resistance during back side wind start-up, ensure that the ignition of the main combustion chamber is not affected by the back side wind intruding into the engine body, and at the same time minimize the impact on the turbofan engine start-up time.

[0044] Regarding the increase in ignition speed and fuel injection speed, referring to the wind pressure resistance PdX, and taking the starter power currently used in high-power turbofan engines as the limit, there is no need to design an additional high-power starter.

[0045] The nozzle exit area A9 of a turbofan engine is typically larger than the throat area A8. Currently, during turbofan engine startup, the nozzle exit area A9 and throat area A8 are generally controlled to be at their maximum values, and the vector angle δA9 is 0º. Figure 3 As shown, this control scheme makes it easy for the back side wind to enter the turbofan engine when starting under high-speed back side wind conditions, generating large wind pressure drag and seriously affecting the starting of the turbofan engine.

[0046] Near the ignition speed, adjust the nozzle exit area A9 and vector angle δA9 to shield the nozzle throat, such as... Figure 4 As shown, this can effectively reduce the wind pressure resistance of turbofan engines when starting under high-speed back wind conditions, thus ensuring the start-up of turbofan engines.

[0047] For the adjustment of nozzle exit area A9 and vector angle δA9, with reference to wind pressure resistance PdX, under the constraints of the nozzle structure itself, it is best to effectively block the nozzle throat without affecting the airflow and exhaust of the turbofan engine, and to promote the starting of the turbofan engine.

[0048] The timing for ignition and fuel supply to the turbofan engine is when Pt6 ≥ Pt6.st + ΔPst and Pt6 ≥ Pt6.st + PdX or n2R ≥ f(ΔPst), where,

[0049] Pt6 is the real-time total turbine exhaust pressure of the turbofan engine;

[0050] Pt6.st is the total turbine exhaust pressure at the start of the turbofan engine;

[0051] ΔPst is the difference between the total pressure at the fan inlet and the total pressure at the turbine exhaust at the start of the turbofan engine.

[0052] n2R is the real-time high-pressure rotor relative conversion speed of the turbofan engine.

[0053] f(ΔPst) is the difference between the total pressure at the fan inlet and the total pressure at the turbine exhaust at the start of the turbofan engine, corresponding to the relative conversion speed of the high-pressure rotor.

[0054] After the turbofan engine is successfully ignited and Pt6 ≥ Pt6.st + C, adjust the nozzle throat area A8 and outlet area A9 to their maximum values, and set the vector angle δA9 to 0º to ensure the airflow within the turbofan engine and the smooth exhaust flow, enabling the turbofan engine to start successfully. Here, C is an adjustable parameter greater than 0, determined based on the premise that the exhaust pressure of the turbofan engine can be significantly higher than the outlet pressure of the nozzle. Specifically, it can be 1.5 PdX or even a larger value.

[0055] Based on the starting fuel injection speed, nozzle throat area A8, outlet area A9, and vector angle δA9 determined by the turbofan engine back-side wind starting method disclosed in the above embodiments, the control law for nozzle throat area A8, outlet area A9, and vector angle δA9 during the starting process can be formed. The control law was used to verify the starting of the turbofan engine under different back wind angles and wind speeds, and the applicability of the control law was verified. Adjustments were made as needed until the high wind speed back wind starting conditions could be reliably identified, the main combustion chamber could be reliably ignited, and the starting time and exhaust temperature met the requirements.

[0056] In a specific example, the nozzle throat area A8, exit area A9, and vector angle are determined during the turbofan engine start-up process. Control laws, such as Figure 5 As shown.

[0057] The turbofan engine backwind starting method disclosed in the above embodiments is designed to effectively identify whether the turbofan engine is starting under high-speed backwind conditions by checking whether the low-pressure rotor is reversing. It also determines the wind pressure resistance of the turbofan engine under high-speed backwind conditions based on the low-pressure rotor's reversal speed. Furthermore, by adjusting the nozzle throat area and ignition and fuel supply speeds during the starting process, it increases the internal flow pressure during ignition to counteract the backwind starting wind pressure resistance. Additionally, by adjusting the nozzle exit area and vector angle, it shields the throat area, reducing the wind pressure resistance during backwind starting at the source. This effectively solves the ignition delay and ignition detonation problems that occur when turbofan engines start under high wind speeds, achieving reliable starting of the turbofan engine. Moreover, it is simple to implement on vector thrust engines, easy to improve, and widely adaptable, greatly saving time, manpower, and economic costs.

[0058] The technical solution of this application has been described in conjunction with the preferred embodiments shown in the accompanying drawings. Those skilled in the art should understand that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A method for starting a turbofan engine with back-side wind, characterized in that, include: Step 1: Identify whether the turbofan engine is starting under high-speed back wind conditions by checking whether the low-pressure rotor is rotating in reverse. If the low-pressure rotor reverses, it indicates that the turbofan engine is starting under high-speed back wind conditions; Step 2: After identifying that the turbofan engine is started under high-speed back crosswind conditions, determine the wind pressure resistance PdX of the turbofan engine when starting under high-speed back crosswind conditions by measuring the low-pressure rotor reversal speed and the correspondence between the low-pressure rotor reversal speed and wind pressure resistance. Step 3: After the low-pressure rotor is driven by the starter to rotate from reverse to forward, reduce the nozzle throat area A8, adjust the nozzle exit area A9 and vector angle δA9 to shield the nozzle throat, increase the ignition speed to ignite the turbofan engine, increase the fuel supply speed to supply fuel to the turbofan engine, and start the turbofan engine. After the turbofan engine is successfully ignited and Pt6≥Pt6.st+C, the nozzle throat area A8 and the exit area A9 are adjusted to their maximum values, and the vector angle δA9 is 0º. Pt6 is the real-time total turbine exhaust pressure of the turbofan engine; Pt6.st is the total turbine exhaust pressure at the start of the turbofan engine; C is an adjustable parameter, set to 1.5 PdX.

2. The turbofan engine back-side wind starting method according to claim 1, characterized in that, In step two, the relationship between the low-pressure rotor reversal speed and the wind pressure resistance is established based on simulation or experimental results.

3. The turbofan engine back-side wind starting method according to claim 2, characterized in that, In step three, the timing for ignition and fuel supply to the turbofan engine is when Pt6 ≥ Pt6.st + ΔPst and Pt6 ≥ Pt6.st + PdX, where... ΔPst is the difference between the total pressure at the fan inlet and the total pressure at the turbine exhaust at the start of the turbofan engine.

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