Piston temperature and stress testing device and method based on fiber bragg grating

Abstract

The present application relates to the technical fields of piston temperature and stress measurement, and particularly relates to a piston temperature and stress testing device and method based on fiber Bragg grating, which is installed on a piston and comprises an FBG sensor, at least two through holes are formed on the surface of a combustion chamber at the top of the piston and are communicated with the inner cavity of the piston, a flexible armored tube is arranged below each through hole in the inner cavity of the piston, the FBG sensor is fixed on the surface of the combustion chamber by high-temperature resistant epoxy resin adhesive, the optical fiber at the input end of the FBG sensor is inserted into the inner cavity of the piston from one through hole, passes out of the piston through the flexible armored tube below the through hole and is connected to a light source, and the optical fiber at the output end of the FBG sensor is inserted into the inner cavity of the piston from another through hole and passes out of the piston through the flexible armored tube below the through hole and is connected to a demodulator. The present application can realize high-precision, real-time and reliable measurement, and can ensure the integrity of the surface of the piston and reduce the influence on the normal operation of the piston.

Description

Technical Field

[0001] This invention relates to the field of piston temperature and stress measurement technology, specifically to a piston temperature and stress testing device and method based on a fiber Bragg grating. Background Technology

[0002] In the field of piston temperature and stress measurement, a variety of techniques are widely used, among which thermocouple method, resistance strain gauge method and infrared thermography method are the more common measurement methods.

[0003] Traditional measurement techniques suffer from significant functional limitations. Thermocouple and infrared thermography methods can only measure temperature, while strain gauge methods are limited to stress measurement. No traditional method can simultaneously acquire both temperature and stress data—two crucial parameters for piston performance analysis. During actual piston operation, the temperature and stress fields couple and influence each other, resulting in a significant thermo-stress coupling effect. The inability to simultaneously measure temperature and stress hinders researchers from comprehensively and accurately analyzing the piston's operating state and performance, severely limiting in-depth research into the piston's thermo-engine coupling behavior and failing to meet the demands for precise piston performance analysis under the complex operating conditions of modern internal combustion engines.

[0004] Traditional measurement methods are unsuitable for environmental adaptability. For example, thermocouple leads are highly susceptible to oxidation at temperatures above 300°C. This oxidation reduces conductivity and can even lead to breakage, severely impacting both the accuracy of measurement data and the stability of the measurement system, significantly compromising the reliability of the results. For resistance strain gauge methods, the adhesives used gradually degrade in adhesion at temperatures above 250°C, resulting in insufficient adhesion between the strain gauge and the piston surface. This hinders the effective transmission of strain signals and may even lead to strain gauge detachment, further affecting the reliability and continuity of the measurement. Infrared thermography is highly susceptible to environmental factors in the combustion chamber. Carbon deposits and oil mist within the combustion chamber alter the propagation path and intensity of infrared radiation, drastically reducing measurement accuracy. It is often difficult to achieve precise piston temperature measurement, thus failing to provide reliable data support for piston thermal management and design.

[0005] In terms of dynamic response, resistance strain gauges have a low response frequency, typically below 10kHz, while the combustion pressure wave frequency of a piston during operation can reach as high as 20kHz. This makes it impossible for resistance strain gauges to track the rapid strain changes caused by the combustion pressure wave in a timely manner, and to fully obtain the stress information of the piston under dynamic conditions. This poses difficulties for studying the mechanical properties of the piston under extreme conditions such as high speed and high load, and makes it difficult to meet the requirements of modern internal combustion engines for piston performance optimization.

[0006] Regarding spatial resolution, traditional measurement methods mostly employ single-point measurements, which cannot reveal the temperature-stress gradient distribution on the piston top surface. For example, in the piston's fire shore region, due to the scouring effect of combustion gases and the non-uniformity of heat transfer, the strain gradient can reach 100 με / mm. Single-point measurements cannot obtain detailed information about such local areas, making it impossible to accurately grasp the stress concentration and abnormal temperature distribution of the piston, which is detrimental to piston structural optimization and fault diagnosis.

[0007] In summary, traditional piston temperature and stress measurement technologies have many shortcomings in terms of functional integrity, environmental adaptability, dynamic response capability, and spatial resolution. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a piston temperature and stress testing device and method based on fiber Bragg gratings. This invention solves the problems of poor electromagnetic interference resistance, complex temperature compensation, slow response speed, complex installation and wiring, and short service life in existing piston temperature and stress measurement methods. It can achieve high-precision, real-time, and reliable measurement, while ensuring the integrity of the piston surface as much as possible and reducing the impact on the normal operation of the piston.

[0009] This invention is achieved through the following technical solution:

[0010] A piston temperature and stress testing device based on a fiber Bragg grating is provided. Mounted on a piston, the device includes an FBG sensor. At least two through holes communicating with the piston's inner cavity are formed on the combustion chamber surface at the top of the piston. A flexible armored tube is correspondingly disposed below each through hole in the piston's inner cavity. The FBG sensor is bonded and fixed to the combustion chamber surface with high-temperature resistant epoxy resin. The optical fiber at the input end of the FBG sensor enters the piston's inner cavity through one through hole, exits through the flexible armored tube below the through hole, and connects to a light source. The optical fiber at the output end of the FBG sensor enters the piston's inner cavity through another through hole, exits through the flexible armored tube below the through hole, and connects to a demodulator.

[0011] In this solution, the fiber optic cable at the output end of the FBG sensor is connected to a demodulator and then to a computer. The demodulator converts the optical signal (wavelength drift data of reflected light) transmitted through the fiber optic cable into temperature and stress electrical signals. The computer then processes, analyzes, and displays the results of the electrical signals. The fiber optic cable at the input end of the FBG sensor is connected to a light source (preferably a superluminescent diode, SLED) at the end that exits the piston. The light source provides incident light to the FBG sensor. After the incident light is transmitted to the FBG sensor via the input fiber optic cable, it undergoes wavelength drift due to changes in piston temperature and stress. The reflected light after the drift is then transmitted to the demodulator via the output fiber optic cable, forming a complete measurement link of "light source → input fiber optic cable → FBG sensor → output fiber optic cable → demodulator → computer".

[0012] Furthermore, each through hole includes a front section groove and a rear section groove that are connected to each other. The length of the front section groove is 5~10mm and the length direction of the front section groove forms a 45° angle with the horizontal plane. The length of the rear section groove is 8~15mm and the length direction of the rear section groove forms a 75° angle with the horizontal plane.

[0013] The two-section slot design solves the problem of the optical fiber needing to be inserted smoothly on the top surface of the piston, while also preventing the difficulty of drilling arc-shaped holes in practical applications.

[0014] Furthermore, the flexible armored tube includes a stainless steel corrugated tube, the outer wall of which is coated with a high-temperature ceramic coating, the inner cavity of which is hourglass-shaped, and the space between the hourglass-shaped inner cavity and the inserted FBG sensor is filled with high-temperature silicone.

[0015] The flexible armored tube has a three-layer structure: the outermost layer is coated with a high-temperature ceramic coating, the middle layer consists of a stainless steel corrugated tube, and the inner layer is made of high-temperature silicone. The inner cavity of the stainless steel corrugated tube is hourglass-shaped, which has two advantages: First, its shape can precisely adapt to the shape of the optical fiber, accommodating the fiber while ensuring its stable fixation within the groove through structural constraints, preventing displacement caused by piston movement and vibration; second, the hourglass-shaped depth and width, designed to fit the fiber, provide ample space for the fiber and work synergistically with the internal high-temperature silicone to further enhance the fixation effect, ensuring the stability of the fiber position and the continuity of signal transmission under complex working conditions. The flexible armored tube has only two sections below each through hole in the piston cavity, covering the optical fiber segment that enters the piston cavity from the through hole. This design specifically protects the critical optical fiber segments in the piston cavity that are susceptible to high temperature and vibration, preventing fiber wear or displacement, while also reducing unnecessary material waste and ensuring the rationality of fiber optic cabling and the reliability of signal transmission.

[0016] Furthermore, the flexible armored tube is fixed in the piston cavity using high-temperature resistant epoxy resin adhesive.

[0017] In one embodiment of the present invention, six through holes are opened on the combustion chamber surface at the top of the piston, which are connected to the piston cavity and located at the same vertex of a regular hexagon. An FBG sensor is inserted between the two through holes at the top of each pair, and a total of three FBG sensors are arranged in a centrally cross distribution.

[0018] This layout allows for the acquisition of piston top surface temperature and stress data from multiple angles, making it suitable for scenarios requiring high overall performance analysis of the piston top surface. It can comprehensively reflect the temperature-stress distribution of the piston top surface.

[0019] In another embodiment of the present invention, four through holes are opened on the combustion chamber surface at the top of the piston, which are connected to the piston cavity and located at the same vertex of a square. An FBG sensor is inserted between the two through holes at the top of each pair, and a total of two FBG sensors are arranged in a centrally cross-shaped distribution.

[0020] This solution reduces the number of holes and lowers installation complexity, making it suitable for applications requiring relatively high measurement accuracy while also emphasizing ease of installation. It can obtain temperature and stress information for key areas on the piston top surface.

[0021] In another embodiment of the present invention, six through holes are opened on the combustion chamber surface at the top of the piston, which are connected to the piston cavity and located at the same vertex of a regular hexagon. FBG sensors are installed between the two upper through holes, the two middle through holes and the two lower through holes, for a total of three FBG sensors arranged in parallel to each other.

[0022] This solution facilitates fiber optic cabling and installation, and is suitable for parallel monitoring of specific areas on the piston top surface. It can effectively monitor temperature and stress changes at different horizontal positions on the piston top surface.

[0023] In another embodiment of the present invention, two FBG sensors are installed inside two through holes on the combustion chamber surface at the top of the piston that communicate with the piston cavity.

[0024] Two FBG optical fibers are used to measure the temperature and stress on the piston top surface area, avoiding the errors caused by measuring with a single optical fiber. This solution has a simple structure and is easy to install. At the same time, it improves the measurement accuracy and stability compared to the measurement method using a single optical fiber. In environments where installation time and control cost requirements are low, it can monitor the basic temperature and stress changes on the piston top surface.

[0025] Furthermore, the FBG sensor has a center wavelength of 1550nm and is inscribed on a single-mode optical fiber with a diameter of 125μm.

[0026] A method for testing piston temperature and stress using a fiber Bragg grating-based device includes the following steps:

[0027] S1. Select the area on the piston surface where the FBG sensor is to be attached and polish and clean it with alcohol. Apply high-temperature resistant epoxy resin evenly to the treated area. Place the FBG sensor with the fiber optic cable connected into the area to ensure that the FBG sensor is in full contact with the piston surface. Use a clamp to fix the FBG sensor and the position of the light beam. Cure at 150°C for 2 hours.

[0028] S2. After the adhesive has cured, insert one end of the single-mode optical fiber through a through hole on the surface of the piston combustion chamber into the piston cavity and then out through the flexible armor tube, and connect it to the demodulator; insert the other end of the single-mode optical fiber through another through hole on the surface of the piston combustion chamber into the piston cavity and then out through the flexible armor tube. Start the piston to run in a simulated working environment. The demodulator monitors the change in the center wavelength of the light reflected by the FBG sensor in real time and records the data every 0.1s.

[0029] S3. Transmit the data acquired by the demodulator to the computer, plot the temperature and stress change curves over time based on the acquired temperature and stress data, analyze the temperature and stress changes of the piston in different working stages based on the curves, analyze the data of multiple working cycles, and determine whether the piston is working normally.

[0030] The beneficial effects of this invention are:

[0031] I. Strong Anti-interference Capability: In the actual working environment of an internal combustion engine, there is complex electromagnetic interference, such as high-frequency electromagnetic radiation generated by the ignition system and electromagnetic interference from electrical equipment. Traditional resistance strain gauges, based on electrical signal transmission, are highly susceptible to these interferences, leading to deviations in measurement results. However, the FBG sensor used in this invention operates on the principle of optical signal transmission. When optical signals propagate in optical fibers, they are almost unaffected by external electromagnetic interference, resulting in more accurate and reliable measurement results. This provides strong support for studying the working state of pistons in complex electromagnetic environments.

[0032] II. Simplified Temperature Compensation: When measuring temperature and stress, the FBG sensor provides a clear temperature-wavelength and stress-wavelength relationship. The demodulator, in conjunction with the algorithm, can quickly process and analyze the measurement data based on the pre-calibrated temperature-wavelength and stress-wavelength correspondences. Unlike traditional resistance strain gauges that require complex hardware circuitry for temperature compensation, the FBG measurement method of this invention only requires software algorithms to achieve accurate temperature compensation, simplifying the structure and operation of the measurement system. This not only reduces the cost of the measurement system but also improves its stability and reliability.

[0033] Third, fast response speed: During operation, the piston experiences rapid temperature and stress changes, such as during the combustion stroke, when temperature and pressure rise sharply in a short period. Traditional thermocouples have a slow response speed and cannot accurately measure these rapidly changing parameters in a timely manner. In contrast, the FBG sensor responds quickly to temperature and stress changes, enabling real-time monitoring of the piston's state during rapid temperature and stress variations. Experimental tests show that compared to thermocouples, the FBG sensor's response speed is approximately 50% faster. The FBG sensor can promptly capture these changes in piston temperature and stress and transmit the data to the demodulation equipment, providing more accurate data for studying the piston's dynamic performance.

[0034] IV. Easy installation: combined with Figure 8 This invention requires only drilling holes at the piston's top edge to mount the FBG sensor on the piston surface via optical fiber, resulting in simple wiring. Compared to the multi-point mounting method of traditional thermocouples and resistance strain gauges, this significantly reduces installation workload and system complexity. Traditional multi-point mounting methods require arranging multiple sensors and complex wiring on the piston, which is not only cumbersome but also prone to circuit failures. In contrast, the installation method of this invention only requires drilling through holes at symmetrical positions on the piston's top edge, passing an optical fiber coated with high-temperature epoxy resin through these holes, and attaching the FBG sensor to key measurement areas on the piston surface, such as the central area and its vicinity. The optical fiber is then routed through a flexible armored tube on the piston side, ultimately connecting to the demodulator. This installation method is simple and easy to implement, effectively shortening installation time and reducing installation costs.

[0035] V. Long Service Life: The high-temperature resistant epoxy resin adhesive and the optical fiber themselves possess excellent chemical stability, effectively protecting the FBG sensor in the high-temperature and highly corrosive working environment of the piston. The FBG sensor is tightly bonded to the piston surface by the high-temperature resistant epoxy resin adhesive. The adhesive evenly covers the area where the sensor contacts the piston, forming a good bonding layer. The adhesive not only ensures that stress and temperature are effectively transferred to the sensor but also prevents corrosive substances on the piston surface from damaging the sensor. The FBG sensor of this invention extends its service life in the high-temperature and highly corrosive working environment of the piston, reduces maintenance costs, and significantly improves the reliability and stability of the measurement system. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the piston top mounting structure in Embodiment 1 of the present invention.

[0037] Figure 2 This is a schematic diagram of the piston top mounting structure in Embodiment 2 of the present invention.

[0038] Figure 3 This is a schematic diagram of the piston top mounting structure in Embodiment 3 of the present invention.

[0039] Figure 4 This is a schematic diagram of the piston top mounting structure in Embodiment 4 of the present invention.

[0040] Figure 5 This is a schematic diagram of the piston top mounting structure in Embodiment 5 of the present invention.

[0041] Figure 6 This is a schematic diagram of the flexible armored tube in this invention.

[0042] Figure 7 This is a schematic diagram of the overall structure of the present invention.

[0043] Figure 8 for Figure 7 A cross-sectional view of the interior of the piston.

[0044] Figure 9 This is a graph showing the relationship between piston top surface temperature and crankshaft rotation angle in Example 1 of this invention.

[0045] Figure 10 This is a graph showing the relationship between piston top surface stress and crankshaft rotation angle in Embodiment 1 of the present invention.

[0046] As shown in the figure:

[0047] 1. Epoxy resin adhesive; 201. Front end slot; 202. Rear end slot; 3. Demodulator; 4. FBG sensor; 401. Input end of FBG sensor; 402. Output end of FBG sensor; 501. High-temperature ceramic coating; 502. Stainless steel corrugated pipe; 503. High-temperature silicone; 6. Computer; 7. Light source. Detailed Implementation

[0048] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to explain the solution.

[0049] Example 1:

[0050] A piston temperature and stress testing device based on a fiber Bragg grating is installed on a piston. It includes an FBG sensor 4. Two through holes communicating with the piston's inner cavity are opened on the combustion chamber surface at the top of the piston. A flexible armored tube is correspondingly arranged below each through hole in the piston's inner cavity. The FBG sensor 4 is bonded and fixed to the combustion chamber surface using high-temperature resistant epoxy resin adhesive 1. The optical fiber of the FBG sensor's input end 401 passes through one through hole into the piston's inner cavity, exits through the flexible armored tube below the through hole, and connects to a light source 7. In this embodiment, the light source 7 is a superluminescent diode (SLED) light source. The optical fiber of the FBG sensor's output end 402 passes through the other through hole into the piston's inner cavity, exits through the flexible armored tube below the through hole, and connects to a demodulator 3.

[0051] Each through hole includes a front section groove 201 and a rear section groove 202 that are connected to each other. The length of the front section groove 201 is 5 mm and the length direction of the front section groove 201 forms a 45° angle with the horizontal plane. The length of the rear section groove 202 is 8 mm and the length direction of the rear section groove 202 forms a 75° angle with the horizontal plane.

[0052] The flexible armored tube is fixed in the piston cavity by high-temperature resistant epoxy resin adhesive 1. The flexible armored tube includes a stainless steel bellows 502, the outer wall of which is coated with a high-temperature ceramic coating 501. The inner cavity of the stainless steel bellows 502 is hourglass-shaped, and the space between the hourglass-shaped inner cavity and the inserted FBG sensor 4 is filled with high-temperature silicone 503.

[0053] Using the testing apparatus and method of this embodiment, piston temperature and stress were measured, and curves showing the relationship between piston top surface temperature and crankshaft rotation angle and piston top surface stress and crankshaft rotation angle were obtained, respectively. Figure 9 and Figure 10 As shown.

[0054] Depend on Figure 9 As can be seen, the temperature change curve with crankshaft angle is smooth and continuous, without abrupt changes or discontinuities, indicating that the FBG sensor can track the rapid temperature fluctuations of the piston during high-speed operation in real time. During the combustion stroke (crankshaft angle 0°~180°), the temperature rises sharply (from 100°C to 400°C), but the curve still maintains high resolution. This verifies the fast response speed of the FBG sensor (approximately 50% faster than traditional thermocouples). The FBG sensor is based on the principle of optical wavelength shift, and its response time is limited only by the speed of light transmission (nanoseconds), while thermocouples rely on thermal conduction and suffer from thermal inertia delay. Figure 9 The steep slope of the rapid rise in the medium temperature curve indicates that the FBG sensor can track the transient temperature fluctuations of the piston in real time during high-speed working cycles (such as 3000 rpm).

[0055] The curves showed no abnormal fluctuations or noise, and the data remained stable even in the internal combustion engine environment where the ignition system generates high-frequency electromagnetic interference. This demonstrates the anti-interference characteristics of the FBG sensor's optical signal transmission.

[0056] Compared to traditional technologies, thermocouple leads are prone to oxidation at temperatures above 300°C, leading to signal distortion. In contrast, FBG sensors transmit optical signals through optical fibers, avoiding electromagnetic interference affecting electrical signals. Figure 9 Its smoothness directly proves its suitability for complex electromagnetic environments.

[0057] Example 1 uses only a single FBG sensor, but Figure 9It can still clearly reflect the periodic temperature change pattern (e.g., peak temperature repeatability error of <±1% for each working cycle). This indicates that the simplified layout is effective enough for monitoring single-point critical areas, avoiding the complexity of traditional multi-point wiring. The through-hole adopts a two-section design (45° angle at the front and 75° angle at the rear) to ensure that the optical fiber is smoothly introduced into the piston cavity, reducing the impact on the piston's structural integrity.

[0058] and Figure 10 Stress curves and temperature curves Figure 9 Temperature curve phase is highly synchronized: During the combustion stroke, the stress increases significantly with the rise in temperature (for example, the stress peak reaches 150MPa), which directly reflects the piston thermal stress coupling effect.

[0059] In traditional methods, resistance strain gauges can only measure stress and require additional equipment to compensate for the effects of temperature; while FBG sensors can acquire temperature and stress data simultaneously through wavelength demodulation. Figure 10 and Figure 9 The correspondence proves that Example 1 achieved true synchronous measurement, providing a complete data link for thermo-mechanical coupling research.

[0060] The stress curves clearly show the rapid changes (up to 20kHz) caused by the combustion pressure wave, without drift or jumps. This indicates that the FBG sensor's response frequency is much higher than that of the resistance strain gauge (typically <10kHz), enabling it to capture the dynamic stress of the piston under extreme conditions.

[0061] The stability of the curve is attributed to the design of the flexible armored tube (with an hourglass-shaped inner cavity filled with high-temperature silicone) and the high-temperature resistant epoxy resin adhesive (cured at 150°C). These structures effectively resist piston vibration and high temperatures, preventing signal attenuation.

[0062] Figure 10 The accuracy of stress data depends on the temperature self-compensation characteristics of the FBG sensor. The demodulator directly separates the influence of temperature and stress based on wavelength drift using an algorithm, eliminating the need for complex hardware circuitry. Compared to traditional resistance strain gauges that require multiple temperature compensation circuits, Example 1 only requires software algorithm processing, reducing system cost and operational complexity.

[0063] pass Figure 9 and Figure 10 Theoretical analysis shows that:

[0064] Accuracy and real-time performance: High dynamic response (0.1s data recording interval) ensures accurate capture of rapid thermo-mechanical changes in the piston.

[0065] Reliability: Electromagnetic interference resistance and stable firmware design (such as flexible armor tube and high-temperature adhesive) extend service life.

[0066] Simplicity: The simplified layout (two through holes) reduces installation costs and time while ensuring monitoring of critical areas.

[0067] Functional integration: Simultaneous measurement of temperature and stress overcomes the limitations of traditional methods.

[0068] This solution is applicable to bench testing and fault diagnosis of internal combustion engine pistons, providing a cost-effective solution for piston performance optimization.

[0069] Example 2:

[0070] like Figure 2 As shown, a piston temperature and stress testing device based on a fiber Bragg grating is installed on a piston. It includes an FBG sensor 4. Six through holes, communicating with the piston's inner cavity and located at the same vertex of a regular hexagon, are formed on the combustion chamber surface at the top of the piston. An FBG sensor 4 is inserted between the two through holes at the top of each pair, resulting in three centrally intersecting FBG sensors 4. A flexible armored tube is correspondingly installed below each through hole in the piston's inner cavity. The FBG sensor 4 is bonded and fixed to the combustion chamber surface using high-temperature resistant epoxy resin adhesive 1. The optical fiber at the input end of the FBG sensor 4 enters the piston's inner cavity through one through hole, exits through the flexible armored tube below the through hole, and connects to a light source 7. The optical fiber at the output end 402 of the FBG sensor enters the piston's inner cavity through another through hole, exits through the flexible armored tube below the through hole, and connects to a demodulator 3.

[0071] Each through hole includes a front section groove 201 and a rear section groove 202 that are connected to each other. The length of the front section groove 201 is 5 mm, and the length direction of the front section groove 202 forms a 45° angle with the horizontal plane. The length of the rear section groove 202 is 8 mm, and the length direction of the rear section groove 202 forms a 75° angle with the horizontal plane.

[0072] The flexible armored tube is fixed in the piston cavity by high-temperature resistant epoxy resin adhesive 1. The flexible armored tube includes a stainless steel bellows 502, the outer wall of which is coated with a high-temperature ceramic coating 501. The inner cavity of the stainless steel bellows 502 is hourglass-shaped, and the space between the hourglass-shaped inner cavity and the inserted FBG sensor 4 is filled with high-temperature silicone 503.

[0073] Example 3:

[0074] A piston temperature and stress testing device based on a fiber Bragg grating (FBG) is mounted on a piston. It includes an FBG sensor 4. Four through holes, communicating with the piston's inner cavity and located at the same vertex of a square, are formed on the combustion chamber surface at the top of the piston. An FBG sensor 4 is inserted between the two through holes at the top of each pair, resulting in two centrally intersecting FBG sensors 4. A flexible armored tube is correspondingly installed below each through hole in the piston's inner cavity. The FBG sensor 4 is bonded to the combustion chamber surface using high-temperature resistant epoxy resin adhesive 1. An optical fiber from the input end 401 of the FBG sensor enters the piston's inner cavity through one through hole, exits through the flexible armored tube below the through hole, and connects to a light source 7. An optical fiber from the output end 402 of the FBG sensor enters the piston's inner cavity through another through hole, exits through the flexible armored tube below the through hole, and connects to a demodulator 3.

[0075] Each through hole includes a front slot 201 and a rear slot 202 that are connected to each other. The length of the front slot 201 is 5 mm and the length direction of the front slot 201 forms a 45° angle with the horizontal plane. The length of the rear slot 202 is 8 mm and the length direction of the rear slot 202 forms a 75° angle with the horizontal plane.

[0076] The flexible armored tube is fixed in the piston cavity by high-temperature resistant epoxy resin adhesive 1. The flexible armored tube includes a stainless steel bellows 502, the outer wall of which is coated with a high-temperature ceramic coating 501. The inner cavity of the stainless steel bellows 502 is hourglass-shaped, and the space between the hourglass-shaped inner cavity and the inserted FBG sensor 4 is filled with high-temperature silicone 503.

[0077] Example 4:

[0078] A piston temperature and stress testing device based on a fiber Bragg grating (FBG) is mounted on a piston. It includes an FBG sensor 4. Six through holes, communicating with the piston's inner cavity and located at the same vertex of a regular hexagon, are formed on the combustion chamber surface at the top of the piston. FBG sensors 4 are inserted between the top two, middle two, and bottom through holes, resulting in three parallel FBG sensors 4. A flexible armored tube is positioned below each through hole in the piston's inner cavity. The FBG sensor 4 is bonded to the combustion chamber surface using high-temperature epoxy resin adhesive 1. The optical fiber at the input end 401 of the FBG sensor enters the piston's inner cavity through one through hole, exits through the flexible armored tube below the through hole, and connects to a light source 7. The optical fiber at the output end 402 of the FBG sensor enters the piston's inner cavity through another through hole, exits through the flexible armored tube below the through hole, and connects to a demodulator.

[0079] Each through hole includes a front section groove 201 and a rear section groove 202 that are connected to each other. The length of the front section groove 201 is 5 mm and the length direction of the front section groove 201 forms a 45° angle with the horizontal plane. The length of the rear section groove 202 is 8 mm and the length direction of the rear section groove 202 forms a 75° angle with the horizontal plane.

[0080] The flexible armored tube is fixed in the piston cavity by high-temperature resistant epoxy resin adhesive 1. The flexible armored tube includes a stainless steel bellows 502, the outer wall of which is coated with a high-temperature ceramic coating 501. The inner cavity of the stainless steel bellows 501 is hourglass-shaped, and the space between the hourglass-shaped inner cavity and the inserted FBG sensor 4 is filled with high-temperature silicone 503.

[0081] Example 5:

[0082] A piston temperature and stress testing device based on a fiber Bragg grating (FBG) is mounted on a piston. It includes FBG sensors 4. Two through holes communicating with the piston's inner cavity are formed on the combustion chamber surface at the top of the piston. Two FBG sensors 4 are inserted into these through holes. A flexible armored tube is correspondingly positioned below each through hole in the piston's inner cavity. The FBG sensors 4 are bonded to the combustion chamber surface using high-temperature resistant epoxy resin adhesive 1. An optical fiber from the input end 401 of the FBG sensor enters the piston's inner cavity through one through hole, exits through the flexible armored tube below the hole, and connects to a light source 7. An optical fiber from the output end 402 of the FBG sensor enters the piston's inner cavity through another through hole, exits through the flexible armored tube below the hole, and connects to a demodulator 3. Using two FBG sensors 4 in conjunction with optical fibers, the temperature and stress in the piston's top surface area are measured separately, avoiding errors caused by measuring with a single optical fiber.

[0083] Each through hole includes a front slot 201 and a rear slot 202 that are connected to each other. The front slot 201 is 10 mm long and the length direction of the front slot 202 forms a 45° angle with the horizontal plane. The rear slot 202 is 15 mm long and the length direction of the rear slot 202 forms a 75° angle with the horizontal plane.

[0084] Example 6:

[0085] A method for testing piston temperature and stress using a fiber Bragg grating-based device includes the following steps:

[0086] S1. Select the area on the piston surface where the FBG sensor 4 is to be attached, and polish and clean it with alcohol. Apply high-temperature resistant epoxy resin 1 evenly to the treated area. Place the FBG sensor 4 with the optical fiber connected into the area, ensuring that the FBG sensor 4 is in full contact with the piston surface. Use a clamp to fix the FBG sensor 4 and the position of the light beam, and cure at 150°C for 2 hours. The center wavelength of the FBG sensor 4 is 1550nm, and it is inscribed on a single-mode optical fiber with a diameter of 125μm.

[0087] S2. After the adhesive has cured, insert one end of the single-mode optical fiber through a through hole on the surface of the piston combustion chamber into the piston cavity and then out through the flexible armor tube, and connect it to the demodulator 3; insert the other end of the single-mode optical fiber through another through hole on the surface of the piston combustion chamber into the piston cavity and then out through the flexible armor tube, and connect it to the light source 7. Start the piston to run in a simulated working environment. The demodulator 3 monitors the change in the center wavelength of the reflected light from the FBG sensor 4 in real time and records the data every 0.1s.

[0088] S3. Transmit the data acquired by the demodulator 3 to the computer 6. Plot the temperature and stress change curves over time based on the acquired temperature and stress data. Analyze the temperature and stress changes of the piston in different working stages based on the curves. Analyze the data of multiple working cycles to determine whether the piston is in normal working condition.

[0089] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A piston temperature and stress testing device based on a fiber Bragg grating, mounted on a piston, characterized in that: Including an FBG sensor, at least two through holes communicating with the piston cavity are opened on the combustion chamber surface at the top of the piston. A flexible armored tube is correspondingly installed below each through hole in the piston cavity. The FBG sensor is bonded and fixed to the combustion chamber surface with high-temperature resistant epoxy resin. The optical fiber at the input end of the FBG sensor enters the piston cavity through one through hole, exits through the flexible armored tube below the through hole, and connects to a light source. The optical fiber at the sensor's output end passes through another through-hole into the piston cavity and then through a flexible armored tube below the through-hole, exiting the piston and connecting to the demodulator. Each through-hole includes an interconnected front slot and a rear slot. The length of the front slot is 5-10 mm, and its length direction forms a 45° angle with the horizontal plane. The length of the rear slot is 8-15 mm, and its length direction forms a 75° angle with the horizontal plane. The flexible armored tube includes a stainless steel corrugated tube with a high-temperature ceramic coating on its outer wall. The inner cavity of the stainless steel corrugated tube is hourglass-shaped, and high-temperature silicone is filled between the hourglass-shaped inner cavity and the inserted FBG sensor. The flexible armored tube is fixed in the piston cavity with high-temperature resistant epoxy resin.

2. The piston temperature and stress testing device based on fiber Bragg grating according to claim 1, characterized in that: The combustion chamber surface at the top of the piston has six through holes that communicate with the piston cavity and are located at the same vertex of a regular hexagon. An FBG sensor is installed between the two through holes at the top of each pair, and a total of three FBG sensors are centrally and cross-distributed.

3. The piston temperature and stress testing device based on fiber Bragg grating according to claim 1, characterized in that: Four through holes are opened on the combustion chamber surface at the top of the piston, which are connected to the piston cavity and located at the same vertex of the square. An FBG sensor is inserted between the two through holes at the top of each pair, and a total of two FBG sensors are arranged in a centrally cross-shaped distribution.

4. The piston temperature and stress testing device based on fiber Bragg grating according to claim 1, characterized in that: The combustion chamber surface at the top of the piston has six through holes that communicate with the piston cavity and are located at the same vertex of a regular hexagon. FBG sensors are installed between the two upper through holes, the two middle through holes, and the two lower through holes, for a total of three FBG sensors arranged in parallel to each other.

5. The piston temperature and stress testing device based on fiber Bragg grating according to claim 1, characterized in that: Two FBG sensors are installed inside two through holes on the combustion chamber surface at the top of the piston, which communicate with the piston cavity.

6. The piston temperature and stress testing device based on fiber Bragg grating according to claim 1, characterized in that: The FBG sensor has a center wavelength of 1550nm and is inscribed on a single-mode optical fiber with a diameter of 125μm.

7. A method for testing piston temperature and stress using the fiber Bragg grating-based device as described in claim 1, characterized in that: Includes the following steps: S1. Select the area on the piston surface where the FBG sensor is to be attached and polish and clean it with alcohol. Apply high-temperature resistant epoxy resin evenly to the treated area. Place the FBG sensor with the fiber optic cable connected into the area to ensure that the FBG sensor is in full contact with the piston surface. Use a clamp to fix the FBG sensor and the position of the light beam. Cure at 150°C for 2 hours. S2. After the adhesive has cured, insert one end of the single-mode optical fiber into the piston cavity through a through hole on the surface of the piston combustion chamber, then out through the flexible armor tube, and connect it to the demodulator. The other end of the single-mode optical fiber is inserted into the piston cavity through another through hole on the surface of the piston combustion chamber and then out through the flexible armor tube. The piston is started to run in a simulated working environment. The demodulator monitors the change in the center wavelength of the light reflected by the FBG sensor in real time and records the data once every 0.1s. S3. Transmit the data acquired by the demodulator to the computer, plot the temperature and stress change curves over time based on the acquired temperature and stress data, analyze the temperature and stress changes of the piston in different working stages based on the curves, analyze the data of multiple working cycles, and determine whether the piston is working normally.

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