Method for avoiding bearing cavity oil leakage when the sealing pressure difference is low and test method

Abstract

The application provides a method for avoiding bearing cavity oil leakage when the sealing pressure difference is low and a test method, the method comprises the following steps: setting a throttling device on an oil supply pipe of an aero-engine oil supply system; when the engine is running at a low speed, controlling the throttling device to generate a throttling effect, reducing the oil supply amount of the bearing cavity and achieving an optimal oil reduction amount, reducing the oil-gas ratio in the bearing cavity, thereby avoiding oil leakage at a low speed or a low state; when the engine speed is higher than a predetermined value, controlling the throttling device to not generate a throttling effect, thereby increasing the sealing air entraining pressure, restoring the normal oil supply state and ensuring effective sealing, thereby achieving the purpose of realizing the external duct air sealing of the engine in all states.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aero-engines, and particularly relates to a method for avoiding bearing cavity oil leakage when the sealing pressure difference is low. BACKGROUND

[0002] When an aero-engine air system scheme is designed, a special flow path needs to be set for guiding the pressurized air in an engine flow channel to a bearing cavity sealing device (including a graphite seal and a labyrinth seal) to serve as bearing cavity sealing bleed air. The sealing pressure difference between the pressure of the sealing bleed air and the pressure of the bearing cavity is controlled to meet the minimum limit value requirement of the bearing cavity sealing, so as to ensure the sealing effect of the bearing cavity. According to the engine design experience and simulation and test results, the sealing pressure difference for ensuring the effective sealing of the graphite seal should not be lower than 5 kPa, and the sealing pressure difference for ensuring the effective sealing of the labyrinth seal should not be lower than 8 kPa.

[0003] The sealing bleed air is generally high-pressure compressor bleed air or outer channel bleed air. The high-pressure compressor bleed air meets the sealing requirement in terms of bleed air pressure when the engine is running at low speed, but the high temperature of the sealing bleed air when the engine is running at high state will affect the service life of the graphite seal sealing device. The outer channel bleed air has a low temperature and is suitable for the sealing of the bearing cavity when the engine is running at high speed or high state, but the low pressure of the bleed air cannot meet the minimum sealing pressure difference requirement when the engine is running at low speed, resulting in bearing cavity oil leakage. SUMMARY

[0004] The purpose of the present application is to provide a method for avoiding bearing cavity oil leakage when the sealing pressure difference is low and a test method, so as to solve or alleviate at least one problem in the background art.

[0005] The technical solution of the present application is: a method for avoiding bearing cavity oil leakage when the sealing pressure difference is low, characterized in that the method comprises:

[0006] A throttling device is arranged on an oil supply pipe of an aero-engine oil supply system;

[0007] When the engine is running at low speed, the throttling device is controlled to generate a throttling effect, the oil supply amount of the bearing cavity is reduced to the optimal oil reduction amount, the oil-gas ratio in the bearing cavity is reduced, and thus the oil leakage at low speed or low state is avoided;

[0008] When the engine speed is higher than a predetermined value, the throttling device is controlled not to generate a throttling effect, so as to increase the sealing bleed air pressure, restore the normal oil supply state, and ensure effective sealing, thereby achieving the purpose of using outer channel bleed air for sealing in all states of the engine.

[0009] Further, the throttling device is a throttle valve or a throttle nozzle.

[0010] Further, the application also provides a test method for determining the optimal oil reduction amount and the minimum sealing air pressure in the method for avoiding oil leakage of the bearing cavity when the sealing pressure difference is low, the test method comprising:

[0011] Step one, arranging pressure measuring points, including sealing air pressure measuring points, bearing cavity pressure measuring points, and ventilation pipe inlet and outlet measuring points;

[0012] Step two, determining the throttling range of the throttling device, assembling an oil reduction throttling device on the oil supply pipe of the oil supply system, the throttling device being set to an initial oil reduction amount, outputting sealing air, and making the sealing air have the same pressure as the slow running state outer duct air pressure on the ground, starting to slow down, staying for a period of time, and then stopping;

[0013] Step three, determining whether the front cavity, middle cavity, and rear cavity have oil leakage;

[0014] Step four, if there is oil leakage, disassembling the high altitude valve to increase the air pressure, keeping the throttling device on the oil supply pipe unchanged, continuing to output sealing air, making the sealing air higher than the predetermined value of the sealing air pressure in the above process, starting to slow down, staying for a period of time, and then stopping;

[0015] Step five, checking again whether the oil leaks, if it leaks, the oil reduction scheme is not applicable, and if it does not leak, recording the sealing air pressure, bearing cavity pressure, and ventilation pipe inlet and outlet pressure under the corresponding oil reduction amount condition;

[0016] Step six, sequentially reducing the oil reduction amount according to a predetermined interval, and repeating the above process until the verification of all oil reduction amounts in the throttling range of the throttling device is completed.

[0017] Further, the sealing air pipeline is connected to a ground air source, for adjusting the sealing air pressure at any time according to different needs.

[0018] Further, the process of determining whether the front cavity, middle cavity, and rear cavity have oil leakage is as follows:

[0019] Front cavity: checking whether there is oil trace on each part of the fan by using a hole probe, and checking whether the oil supply pipe joint and fulcrum graphite are physically damaged by using a hole probe;

[0020] Middle cavity: checking whether there is oil trace on the surface of the compressor and turbine blades by using a hole probe;

[0021] Rear cavity: checking the outer duct below the rear cavity by using a hole probe, and visually checking whether there is oil trace in the rear cavity support plate, blades, and tail jet flow passage.

[0022] Further, in step four, the sealing air is at least 50 kPa higher than the predetermined value of the sealing air pressure in the previous step.

[0023] The method and test method for bearing cavity oil leakage when the wall sealing differential pressure is low can realize that the bearing cavity does not appear oil leakage at low speed, and the optimal oil reduction amount of the engine at low speed can be obtained according to the determination method of the corresponding optimal oil reduction amount and the minimum sealing air pressure, which has good applicability to multiple types of engines. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions provided by the present application, the following will briefly introduce the drawings. Obviously, the drawings described below are only some embodiments of the present application.

[0025] Figure 1 It is a schematic diagram of a traditional engine oil system.

[0026] Figure 2 It is a schematic diagram of the engine oil system measurement point arrangement position in the present application.

[0027] Figure 3 It is a process flow chart of the test run test in the present application. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the embodiments of the present application will be described in more detail below in combination with the drawings in the embodiments of the present application.

[0029] Figure 1 It is a schematic diagram of a traditional engine oil system (including oil supply / return system and ventilation system), and the bearing cavity is divided into front cavity 11, middle cavity 12 and rear cavity 13.

[0030] The oil supply system 40 supplies oil to the support bearings of the front cavity 11, the middle cavity 12 and the rear cavity 13 through the oil supply pipes respectively.

[0031] The outer duct sealing air 20 is connected to the sealing structure of the front cavity 11, the middle cavity 12 and the rear cavity 13 of the engine respectively.

[0032] The ventilation system includes front cavity ventilation pipe 51, middle cavity ventilation pipe 52 and rear cavity ventilation pipe 53, and the front cavity ventilation pipe 51, the middle cavity ventilation pipe 52 and the rear cavity ventilation pipe 53 are connected to the front cavity 11, the middle cavity 12 and the rear cavity 13 respectively, and collect air to the engine casing 54.

[0033] If the engine uses outer duct sealing air for bearing cavity sealing throughout the whole process, it will result in insufficient sealing differential pressure at low speed, and it is easy to cause oil leakage.

[0034] In order to avoid oil leakage pollution of the main flow channel, an oil leakage collecting structure is usually arranged at the position of each bearing cavity of the engine, i.e., the front cavity oil collecting structure 31, the middle cavity oil collecting structure 32 and the rear cavity oil collecting structure 33, to collect the leaked lubricating oil and discharge it periodically. However, the oil collecting structure in the prior art is complex and is not conducive to the weight control of the engine.

[0035] The above structure causes the lubricating oil to leak mainly due to the following two aspects:

[0036] 1) When the outer channel sealing air is used in the ground slow running state of the engine, if the graphite seal is used at the rear cavity 13, the sealing pressure difference of the sealing structure at the rear cavity 13 is 5 kPa, and if the labyrinth seal is used at the rear cavity 13, the sealing pressure difference of the sealing structure at the rear cavity 13 is only 3.5 kPa, which does not meet the requirement that the effective sealing pressure difference of the graphite seal should not be lower than 5 kPa and the effective sealing pressure difference of the labyrinth seal should not be lower than 8 kPa;

[0037] 2) The engine uses a constant pressure difference oil supply form, i.e., the lubricating oil supply amount of the engine is basically consistent at different speeds, and only a small amount of lubricating oil is needed at low speed of the engine to meet the needs of bearing lubrication and cooling. When the lubricating oil supply amount is large, the oil-gas ratio in the bearing cavity is high, which is easy to cause the lubricating oil to leak from the sealing structure under the stirring action of the rotor.

[0038] In order to solve the problem of lubricating oil leakage in the bearing cavity due to the fact that the sealing air cannot meet the sealing requirement of the bearing cavity at low speed when the engine uses the outer channel air for sealing, the application provides a method for avoiding lubricating oil leakage in the bearing cavity when the sealing pressure difference is low.

[0039] The method for avoiding lubricating oil leakage in the bearing cavity when the sealing pressure difference is low provided by the application is:

[0040] S1, a throttling device is arranged on the oil supply pipe of the oil supply system 40;

[0041] S2, when the engine is running at low speed, the throttling device is controlled to generate a throttling effect, the oil supply amount of the bearing cavity is reduced and the optimal oil reduction amount is achieved, the oil-gas ratio in the bearing cavity is reduced, and thus the lubricating oil leakage at low speed or low state is avoided;

[0042] S3, when the engine speed is higher than a predetermined value, the throttling device is controlled not to generate a throttling effect, so as to increase the sealing air pressure, restore the normal oil supply state and ensure effective sealing, thereby achieving the purpose of using the outer channel air for sealing in all states of the engine.

[0043] In the above scheme, the throttling device usually uses a throttle valve or a throttle nozzle.

[0044] In the above method of this application, since excessive oil reduction at low engine speed may lead to insufficient lubrication and cooling of the main bearing, it is necessary to determine the optimal oil reduction amount and the minimum value of the sealing bleed air pressure to ensure effective lubrication of the bearing while preventing oil leakage.

[0045] Therefore, this application also provides a test method for determining the optimal oil reduction amount and the minimum sealing venting pressure in the above-mentioned oil leakage prevention method. Taking the reduction of oil in the rear cavity as an example, the test method includes the following process:

[0046] I. Pressure Measurement Point Layout and Gas Source Improvement

[0047] like Figure 2 As shown, in order to determine the optimal oil reduction amount and minimum sealing bleed pressure of the rear cavity 13, relevant pressure measuring points are arranged, including sealing bleed pressure measuring points, bearing cavity pressure measuring points, and ventilation pipe inlet and outlet measuring points. Specifically, pressure measuring point P1 is set at the inlet end of the rear cavity ventilation pipe 53 connected to the rear cavity 13, pressure measuring point P2 is set at the outlet end of the rear cavity ventilation pipe 53, pressure measuring point P4 is set inside the rear cavity 13, and pressure measuring point P3 is set at the sealing bleed point connected to the rear cavity 13.

[0048] In this application, the lubricating oil supply / return temperature is monitored simultaneously.

[0049] To facilitate adjustment of the sealing venting pressure, the sealing venting pipeline is connected to the ground gas source 20', allowing the sealing venting pressure to be adjusted at any time according to different needs.

[0050] II. Verification Test Run

[0051] like Figure 3 The diagram shown is a flowchart of the test run process in the method of this application. First, the throttling range of the throttling device is determined. Then, starting from the maximum fuel reduction of the throttling device, the test is carried out step by step. The specific process includes:

[0052] 1) A throttling device is installed on the oil supply pipe of the oil supply system. The throttling range of the throttling device can achieve a predetermined amount of oil reduction. For example, in this embodiment of the application, the throttling device can achieve an oil reduction of 50% to 10%. Because it has been evaluated that when the oil supply is below 50%, there may be insufficient bearing lubrication and cooling, the initial oil reduction amount in this embodiment of the application is 50%. Other engines can adjust the maximum oil reduction amount according to the actual situation.

[0053] Control the ground air source 20' to output sealed bleed air, so that it is the same as the bleed air pressure of the external bypass duct in the ground slow-speed state;

[0054] Start the engine at low speed, pause for a period of time, and then stop, depending on the situation. For example, you can pause for 5 to 10 minutes.

[0055] 2) Determine whether there is oil leakage for the front cavity, middle cavity and rear cavity, and the determination method is as follows:

[0056] Front cavity: Check the fan with a hole probe, check whether there are oil marks on the blade tip and blade root, etc., and check whether the graphite of the oil supply pipe joint and the 1 fulcrum is physically damaged;

[0057] Middle cavity: Check whether there are oil marks on the surface of the compressor and turbine blades with a hole probe;

[0058] Rear cavity: Check the outer duct below the rear cavity with a hole probe, and visually check whether there are oil marks in the rear cavity support plate, blades and tail nozzle flow channel.

[0059] 3) If the oil leaks, remove the high-altitude valve to increase the bleed air pressure, purge the leaked oil, keep the throttle device on the oil supply pipe unchanged, control the ground air source output to seal the bleed air, and make it higher than the sealing bleed air pressure in the previous step by a certain value, for example, the predetermined value can be set to at least 50 kPa;

[0060] Start to slow down, stop for a period of time, for example, 5-10 minutes, and then stop, which can be determined according to the site situation;

[0061] 4) Check again whether the oil leaks, if it leaks, the oil reduction scheme is not applicable, if it does not leak, record the sealing bleed air pressure, bearing cavity pressure, ventilation pipe inlet and outlet pressure and other parameters under the corresponding oil reduction condition, and calculate the sealing pressure difference (the difference between the bleed air pressure and the bearing cavity pressure) and the ventilation pipe resistance (the difference between the ventilation pipe inlet pressure and the outlet pressure) according to the above parameters;

[0062] 5) Reduce the oil reduction amount in turn according to the predetermined interval (i.e. reduce the oil by 50%, 40%, 30%, 20% and 10%), and repeat the above process until the verification of all oil reduction amounts in the throttling range of the throttle device is completed.

[0063] After all the tests in the above process, the rear cavity oil reduction scheme in this embodiment of the application can obtain conclusions 1-11 shown in Table 1.

[0064] Table 1 Test conclusions and analysis

[0065]

[0066] The method for bearing cavity oil leakage when the wall sealing pressure difference is low provided in the application can realize that the bearing cavity will not leak oil at low speed, and the determination method of the corresponding best oil reduction amount and the minimum sealing bleed air pressure can obtain the best oil reduction amount of the engine at low speed, which has good applicability to multiple types of engines.

[0067] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A test method for determining the optimal oil reduction amount and the minimum sealing bleed pressure in methods to avoid oil leakage in the bearing cavity when the sealing pressure differential is low, wherein, Methods to avoid oil leakage in the bearing cavity when the sealing pressure difference is low include: installing a throttling device on the oil supply pipe of the aero-engine oil supply system; when the engine is running at low speed, controlling the throttling device to produce a throttling effect, reducing the oil supply to the bearing cavity and achieving the optimal oil reduction, reducing the oil-air ratio in the bearing cavity, thereby avoiding lubricating oil leakage at low speed or low conditions; when the engine speed is higher than a predetermined value, controlling the throttling device not to produce a throttling effect. The test method includes: Step 1: Set up pressure measuring points, including sealing and venting pressure measuring points, bearing cavity pressure measuring points, and ventilation pipe inlet and outlet measuring points; Step 2: Determine the throttling range of the throttling device. Install the oil reduction throttling device on the oil supply pipe of the oil supply system. Set the maximum oil reduction of the throttling device to the initial oil reduction. Output sealing bleed air so that the sealing bleed air pressure is the same as the bleed air pressure of the external bypass in the ground slow state. Start to slow, stay for a period of time, and then stop. Step 3: Determine whether there is any lubricating oil leakage in the front cavity, middle cavity, and rear cavity; Step 4: If lubricating oil leaks, remove the high-altitude valve to increase the bleed air pressure, keep the throttling device on the oil supply pipe unchanged, continue to output sealing bleed air, and make the sealing bleed air pressure higher than the predetermined value of sealing bleed air pressure in the above steps. Start the engine at idle speed, stay for a period of time, and then stop. Step 5: Check again for oil leakage. If there is leakage, the oil reduction plan is not applicable. If there is no leakage, record the sealing bleed air pressure, bearing cavity pressure, and ventilation pipe inlet and outlet pressure under the corresponding oil reduction conditions. Step 6: Reduce the amount of fuel reduction sequentially at predetermined intervals, and repeat the above process until the verification of all fuel reduction amounts within the throttling range of the throttling device is completed.

2. The test method as described in claim 1, characterized in that, The sealed air intake pipeline is connected to a ground-based air source, allowing for adjustments to the sealed air intake pressure as needed.

3. The test method as described in claim 1, characterized in that, The process for determining whether there is lubricating oil leakage in the front, middle, and rear chambers is as follows: Front chamber: Use a borescope to check for oil stains in various parts of the fan, and check the oil supply pipe joint and the fulcrum graphite for physical damage. Middle cavity: Use a borescope to check for oil stains on the surface of the compressor and turbine blades; Rear chamber: Use a borescope to inspect the outer bypass duct below the rear chamber, and visually inspect the rear casing support plate, blades, and tail nozzle flow channel for oil stains.

4. The test method as described in claim 1, characterized in that, In step four, the sealing bleed pressure is made at least 50 kPa higher than the predetermined sealing bleed pressure in the previous step.

5. The test method as described in claim 1, characterized in that, The throttling device is a throttling valve or a throttling nozzle.

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