A calibration method for describing the melting characteristics of volcanic ash particles in aircraft engines

Abstract

The present invention belongs to the technical field of material meltability testing and calibration, and proposes a calibration method for describing the melting characteristics of volcanic ash particles in an aircraft engine. The steps are as follows: (1) polishing a platinum-rhodium alloy sheet; (2) placing volcanic ash particles on the surface of the platinum-rhodium alloy sheet, placing the sheet in a heating furnace, and filling it with a reaction atmosphere gas; (3) heating and cooling the volcanic ash particles, and recording the entire process with a camera; (4) combining the camera-recorded images and the heating and cooling data to calibrate four characteristic temperatures. By studying the shape changes of volcanic ash particles during high-temperature melting, the present invention proposes characterizing the melting characteristics of volcanic ash particles using four characteristic temperatures.

Description

Technical Field

[0001] The present invention relates to the technical field of material fusibility test calibration, and in particular to a calibration method for describing the melting characteristics of volcanic ash particles in an aircraft engine. Background Art

[0002] Volcanic ash plays a crucial role in the operating environment of aircraft engines. When tiny particles from volcanic eruptions reach high altitudes, they can be carried by air currents into aircraft engines in flight. The silicate content in volcanic ash is highly fusible at high temperatures. When these particles adhere to the surface of aircraft engine blades, they rapidly melt and form a layer of glassy deposits. This deposit not only affects the aerodynamic performance of the blades but can also cause overheating, structural damage, and even engine failure or shutdown. Therefore, accurately describing and understanding the meltability of volcanic ash is crucial for preventing potential aircraft engine failures during volcanic eruptions.

[0003] Although the potential threat of volcanic ash to aircraft engines is widely recognized, research on its meltability remains relatively limited. Existing meltability test methods, such as those specified in PD CEN / TR 15404:2010, are primarily used to analyze the meltability of solid fuel ash. These test methods typically describe the behavior of ash at high temperatures by measuring certain standardized temperature points, such as deformation temperature, hemispherical temperature, and flow temperature. However, these standard definitions use ash pressed into ash columns and determine the standardized temperature points based on the shape characteristics of the ash columns at high temperatures. The shape characteristics of ash columns differ significantly from those of actual volcanic ash particles. Furthermore, volatile gases are generated in the ash columns during the melting process. These gases, which are not promptly removed, also affect the sample shape characteristics and, consequently, the meltability calibration. Therefore, these methods cannot effectively reflect the complex melting behavior of volcanic ash.

[0004] Given the limitations of existing methods, accurately describing the shape changes of spherical particles prepared from volcanic ash during the melting process is particularly important. However, existing definitions of meltability are relatively general and fail to capture the morphological changes of spherical particles during melting. This limitation leads to significant uncertainty in the practical application of volcanic ash, especially in fields such as aeroengines that require material stability at high temperatures. Therefore, it is urgent to develop a calibration method that can accurately describe the melting behavior of spherical particles to improve the performance prediction and control of volcanic ash in high-temperature applications. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention proposes a calibration method for describing the melting characteristics of volcanic ash particles in aircraft engines. Different from the traditional ash fusibility test method, which has limitations in describing the melting behavior of spherical particles, especially volcanic ash particles, the present invention proposes to analyze the melting characteristics of volcanic ash particles by calibrating the four characteristic temperatures of volcanic ash during the high-temperature melting deformation process.

[0006] The technical solutions of the present invention are as follows:

[0007] A calibration method for describing the melting characteristics of volcanic ash particles in an aircraft engine comprises the following steps:

[0008] Step S1: polishing the platinum-rhodium alloy sheet;

[0009] Step S2: placing volcanic ash particles on the surface of a platinum-rhodium alloy sheet, placing the sheet in a heating furnace, and filling it with a reaction atmosphere gas;

[0010] Step S3: performing a temperature control process on the volcanic ash particles, and recording the entire process with a camera;

[0011] Step S4: Combine the images recorded by the camera and the temperature rise and fall data to calibrate the following four characteristic temperatures:

[0012] Softening temperature: the temperature at which the contact angle of volcanic ash particles decreases to 97% of the initial contact angle;

[0013] Critical wetting temperature: the temperature at which the contact angle of volcanic ash particles reaches 90°;

[0014] Fast-slow spreading critical point temperature: the temperature at which the contact angle of volcanic ash particles decreases to 20% of the initial contact angle;

[0015] Complete spreading temperature: the temperature at which the contact angle of volcanic ash particles reaches its minimum.

[0016] Preferably, the size of the platinum-rhodium alloy sheet is (10-20 mm)×(10-20 mm)×(0.5-3 mm).

[0017] Preferably, in step S1, the polishing is performed using 800, 1000, 1500 and 2000 grit sandpaper respectively, and the polishing time of each type of sandpaper is not less than 1 minute, and the surface is dried after polishing.

[0018] Preferably, in step S2, the platinum-rhodium alloy sheet is placed horizontally in the heating furnace.

[0019] Preferably, in step S2, the reaction atmosphere gas flows through the volcanic ash particles at a minimum linear velocity of 50-300 mm / min, and the reaction atmosphere gas fills the heating furnace and then stands for 5-20 minutes; the reaction atmosphere gas is an oxidizing gas or a reducing gas.

[0020] Preferably, the temperature increase and decrease in step S3 is carried out in the following manner:

[0021] Below 500℃, adopt a heating rate of 50-100℃ / min; from 500-800℃, adopt a heating rate of 20-30℃ / min; above 800℃, adopt a heating rate of 3-15℃ / min; cool down at a cooling rate of 5-15℃ / min to reduce the furnace temperature to below 50℃.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The calibration method proposed in this invention for describing the melting characteristics of volcanic ash particles in aircraft engines can accurately describe the melting behavior of volcanic ash spherical particles. By calibrating four key angles and their corresponding temperatures - softening temperature (97% initial contact angle θ0), critical wetting temperature (contact angle of 90°), fast and slow spreading critical point temperature (20% initial contact angle θ0) and complete spreading temperature (minimum contact angle θ e ), this method can accurately predict the softening, spreading, and final penetration behavior of volcanic ash at different temperatures. Its specific applications include: First, by evaluating the softening temperature of different CMAS compositions at high temperatures, it can provide a basis for the selection of coating materials, optimize their initial corrosion resistance, reduce the risk of coating failure due to early softening, and ensure safe engine operation. Second, using the critical wetting temperature as an evaluation indicator, it can determine the starting point of CMAS spreading on the coating surface, providing data support for the design of coating material stability at high temperatures, ensuring effective protection against volcanic ash erosion. Furthermore, by measuring the critical temperature of fast and slow spreading, it is possible to evaluate the fluidity of CMAS under high temperature conditions, providing a technical basis for selecting coating materials with superior high-temperature spreading resistance and improving coating performance. Finally, determining the complete spreading temperature can predict the penetration depth of CMAS when fully melted, which is crucial for the corrosion resistance and long-term stability of coating materials under extreme conditions. In summary, this invention provides important theoretical basis and technical support for the optimized design, material selection, and quality control of aircraft engine coatings, promoting the development of new high-temperature resistant coating materials, improving the overall performance and reliability of aircraft engines, and ensuring aviation safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. By referring to the drawings, the features and advantages of the present invention can be more clearly understood. The drawings are schematic and should not be understood as limiting the present invention in any way. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1 The present invention is a flow chart of a calibration method for describing the melting characteristics of volcanic ash particles in an aircraft engine.

[0026] Figure 2 Schematic diagram of the operation scenario of the calibration method of the present invention.

[0027] Figure 3 It is the real-time shape feature of volcanic ash particles corresponding to the four characteristic temperatures. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features therein can be combined with each other without conflict.

[0029] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0030] like Figure 3 As shown, the present invention studies the shape changes of volcanic ash particles during high-temperature melting and finds four characteristic angles and characteristic temperatures that can characterize their melting characteristics, namely:

[0031] (1) Softening temperature: The contact angle of volcanic ash particles begins to change. When the contact angle decreases to 97% of the initial contact angle, it indicates that the melting process begins and the shape of the particles begins to change. The temperature at this time is the softening temperature.

[0032] (2) Critical wetting temperature: The contact angle of volcanic ash particles just reaches 90°. According to Young's equation:

[0033] γ SG =γ SL +γ LG cosθ

[0034] Where, γ SG is the solid-gas interfacial tension, γ SL is the solid-liquid interfacial tension, γLG is the liquid-gas interfacial tension, and θ is the contact angle.

[0035] When the contact angle θ = 90°, the solid-gas interface energy is equal to the solid-liquid interface energy, and the system reaches a critical equilibrium state, indicating that the particles begin to transition from a non-wetting state to a wetting state, and the corresponding temperature is the critical wetting temperature.

[0036] (3) Fast-to-slow spreading critical point temperature: As the contact angle decreases, the rate of contact angle decrease also changes. When the contact angle becomes 20% of the initial contact angle, the rate of contact angle decrease of the volcanic ash particles slows down significantly, transitioning from a rapid decrease to a slow decrease. The corresponding temperature at this point is the fast-to-slow spreading temperature.

[0037] (4) Complete spreading temperature: When the contact angle of volcanic ash particles no longer changes with temperature, the particles have reached the limit of spreading degree, and the corresponding temperature is the complete spreading temperature.

[0038] During the melting process of volcanic ash particles, the above four characteristic temperatures are calibrated, such as Figure 1-2 As shown, the following steps are required:

[0039] Step S1: Polish the platinum-rhodium alloy sheet to eliminate the influence of roughness on subsequent tests.

[0040] Polishing begins with pre-treatment with sandpaper. Polishing is performed using 800-, 1000-, 1500-, and 2000-grit sandpaper, with each type of sandpaper polishing for at least 1 minute. After polishing, wet polishing is performed using a polishing cloth. Diamond polishing paste is used as the polishing medium, along with an appropriate amount of deionized water. The polishing time should be at least 10 minutes. The polished platinum-rhodium alloy sheet is then oven-dried at 100°C.

[0041] Step S2: Place the volcanic ash particles on the surface of the platinum-rhodium alloy sheet and place them together in the sample table of the heating furnace. Then turn on the gas flow meter to allow the reaction atmosphere gas to fill the furnace cavity.

[0042] The heating furnace must reach a maximum temperature of 1500-2000°C, and the chamber must be airtight. The platinum-rhodium alloy sheet must be placed horizontally to avoid errors in subsequent testing caused by non-level surfaces. The reaction atmosphere gas flows through the volcanic ash particles at a minimum linear velocity of 50-300 mm / min. After the reaction atmosphere fills the furnace, it is allowed to stand for 5-20 minutes. The reaction atmosphere gas can be either an oxidizing or reducing gas.

[0043] Step S3: The volcanic ash particles are subjected to temperature rise and fall processing, and the entire process is recorded using a camera.

[0044] The heating and cooling method is as follows: below 500°C, use a heating rate of 50-100°C / min; from 500-800°C, use a heating rate of 20-30°C / min; above 800°C, use a heating rate of 3-15°C / min; and cool down at a rate of 5-15°C / min until the furnace temperature drops below 50°C. The camera takes a photo every 1-3°C.

[0045] Step S4: calibrate four characteristic temperatures by combining the images recorded by the camera and the temperature rise and fall data.

[0046] Example 1

[0047] Select a platinum-rhodium alloy sheet measuring 12×12×1mm for polishing. Select a relatively flat side of the platinum-rhodium alloy sheet and polish it on 800-grit grit paper for 2 minutes. Observe the surface after polishing. If there are no obvious uneven defects, proceed to the next step. Otherwise, continue polishing with 800-grit sandpaper for an extended period. Next, rotate the sample surface 90° clockwise with 1000-grit sandpaper and polish for 3 minutes. Observe that the scratches completely cover those from the previous step before proceeding to the next step. Select 1500-grit sandpaper and rotate the sample surface 90° clockwise with 1500-grit sandpaper and polish for 3 minutes. Observe that the scratches completely cover those from the previous step before proceeding to the next step. Follow the above steps to polish with 2000-grit sandpaper. After polishing with all the sandpaper, select a polishing cloth for further polishing. Secure the polishing cloth to the polishing machine's rotating disk and apply an appropriate amount of diamond polishing paste to the cloth. Once the preparation is complete, place the sample on the polishing cloth and gently press it with your fingers to secure it. Then, turn on the polishing machine's rotary switch and select a speed of 400 rpm. During the polishing process, a small amount of deionized water was continuously added, and the polishing time was 15 min. The polished samples were naturally dried in an oven.

[0048] Place the polished platinum-rhodium alloy sheet onto the sample stage in the heating furnace, ensuring it is level. Otherwise, subsequent samples may slip. After this inspection, place a 2mm diameter volcanic ash particle at the center of the platinum-rhodium alloy sheet and close the furnace door. Turn on the camera to observe the sample and adjust the sample image to the center of the field of view. Fine-tune the focus to ensure a clear sample outline. Set the camera to capture a photo every 1°C.

[0049] Select carbon dioxide as the atmosphere gas, open the cylinder valve, and set the gas flow meter to 100 mm / min. The gas will then begin to flow into the furnace chamber at a constant rate. To ensure that the carbon dioxide fully fills the chamber, wait 15 minutes after setting the gas flow meter before proceeding to the next step.

[0050] When setting the heating and cooling program, the heating rate is set in stages. When heating, select 80°C / min for temperatures below 500°C, 20°C / min for temperatures between 500-800°C, and 5°C / min for temperatures above 800°C. When cooling, select 10°C / min to lower the furnace temperature to 30°C.

[0051] The above steps were repeated three times, with the temperature ramp data and real-time camera image data from each run being exported. The specific values ​​of the four characteristic temperatures were then extracted. The characteristic temperatures obtained from the three tests were: softening temperatures of 941°C, 944°C, and 944°C; critical wetting temperatures of 1017°C, 1015°C, and 1016°C; fast-slow spreading critical temperatures of 1158°C, 1155°C, and 1159°C; and complete spreading temperatures of 1271°C, 1275°C, and 1276°C. Calculations showed that the difference between the maximum and minimum values ​​of each characteristic temperature across the three tests was less than 5°C, indicating reasonable and accurate test results. The final four characteristic temperatures, after averaging, were: softening temperature of 943°C, critical wetting temperature of 1016°C, fast-slow spreading critical temperature of 1157.3°C, and complete spreading temperature of 1274°C. The volcanic ash particle shapes determined at each characteristic temperature were verified to be consistent with the original real-time image data.

[0052] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0053] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0054] In the present invention, the terms "first", "second", "third", and "fourth" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "plurality" refers to two or more, unless otherwise clearly defined.

[0055] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A calibration method for describing the melting characteristics of volcanic ash particles in an aircraft engine, characterized in that: The following steps are involved: Step S1: polishing the platinum-rhodium alloy sheet; Step S2: placing volcanic ash particles on the surface of a platinum-rhodium alloy sheet, placing the sheet in a heating furnace, and filling it with a reaction atmosphere gas; Step S3: performing a temperature control process on the volcanic ash particles, and recording the entire process with a camera; Step S4: Combine the images recorded by the camera and the temperature rise and fall data to calibrate the following four characteristic temperatures: Softening temperature: the temperature at which the contact angle of volcanic ash particles decreases to 97% of the initial contact angle; Critical wetting temperature: the temperature at which the contact angle of volcanic ash particles reaches 90°; Fast-slow spreading critical point temperature: the temperature at which the contact angle of volcanic ash particles decreases to 20% of the initial contact angle; Complete spreading temperature: the temperature at which the contact angle of volcanic ash particles reaches its minimum.

2. The calibration method according to claim 1, characterized in that: The size of the platinum-rhodium alloy sheet is (10-20 mm)×(10-20 mm)×(0.5-3 mm).

3. The calibration method according to claim 1, characterized in that: In step S1, the polishing is performed using 800, 1000, 1500 and 2000 grit sandpaper respectively, and the polishing time of each type of sandpaper is not less than 1 minute. The surface is dried after polishing.

4. The calibration method according to claim 1, characterized in that: In step S2, the platinum-rhodium alloy sheet is placed horizontally in the heating furnace.

5. The calibration method according to claim 1, characterized in that: In step S2, the reaction atmosphere gas flows through the volcanic ash particles at a minimum linear velocity of 50-300 mm / min, and the reaction atmosphere gas fills the heating furnace and then remains stationary for 5-20 minutes.

6. The calibration method according to claim 1, characterized in that: The reaction atmosphere gas is an oxidizing gas or a reducing gas.

7. The calibration method according to claim 1, characterized in that: The temperature increase and decrease in step S3 is carried out in the following manner: Below 500℃, use a heating rate of 50-100℃ / min; 500-800℃, use a heating rate of 20-30℃ / min; When the temperature is above 800℃, a heating rate of 3-15℃ / min is used; when cooling, a cooling rate of 5-15℃ / min is used to reduce the furnace temperature to below 50℃.

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