Airborne auxiliary power unit oil cooler air path wing washing method

Abstract

This application relates to the field of aviation oil cooler cleaning technology, and provides a method for cleaning the air passage of an aviation auxiliary power unit oil cooler on the wing, including: S1, introducing compressed air from the bottom outlet of the oil cooler air passage in the opposite direction to the working airflow; S2, mixing an alkaline water-based concentrated cleaning agent and deionized water at a volume ratio of 1:5 to form a cleaning solution; S3, injecting the cleaning solution from the top inlet of the oil cooler while simultaneously turning on an ultrasonic generator; S4, draining the cleaning solution and removing the ultrasonic generator; S5, performing a reverse flush; S6, replacing the deionized water and performing a forward flush; S7, if the pH value is less than 8.5, proceeding to step S8; if the pH value is greater than or equal to 8.5, repeating steps S5 and S6; S8, introducing compressed air from the top inlet of the oil cooler in the direction of the working airflow. This application enables cleaning of the oil cooler air passage without disassembling the aircraft.

Description

Technical Field

[0001] This application relates to the field of aviation lubricating oil cooler cleaning technology, and more specifically, to an on-wing cleaning method for the air passage of an aviation auxiliary power unit lubricating oil cooler. Background Technology

[0002] Currently, for APUs used on the wing, when the oil cooler's air passage is blocked, the common practice is to remove the oil cooler from the aircraft for cleaning. While this method achieves the cleaning purpose, it has significant drawbacks: First, the disassembly and reassembly process is complex, requiring the removal of multiple pipes and accessories, consuming a significant amount of maintenance time, and is prone to oil leakage during the process, polluting the environment and posing a risk of insufficient oil volume after leakage. Second, after the oil cooler is reinstalled, a ground test of the APU is required to check the installation condition and the oil system's sealing performance, a cumbersome procedure that further increases maintenance time and costs. Third, off-site cleaning requires sending the oil cooler to a professional cleaning facility, resulting in long transportation and waiting times, hindering rapid response to line maintenance needs and impacting aircraft availability. Fourth, existing off-site cleaning methods often use simple circulating rinsing or soaking, which is insufficient to thoroughly remove stubborn dirt deep within the air passage fins, leading to inconsistent cleaning results and often requiring repeated disassembly and cleaning. Summary of the Invention

[0003] This application aims to at least address the problem in the related technology that, when the air passage of the oil cooler is blocked in the existing on-wing APU, it is usually necessary to remove the oil cooler from the aircraft and clean it, which makes the disassembly and assembly process complicated, time-consuming, and requires a test run to check the installation status for reassembly, making the procedure cumbersome and complicated.

[0004] To solve the above-mentioned technical problems, this application is implemented as follows: This application provides a method for on-wing cleaning of the air passage of an aviation auxiliary power unit oil cooler, comprising: introducing compressed air from the bottom outlet of the oil cooler air passage in the opposite direction to the working airflow, and maintaining the air passage pressure at 15 PSIG~30 PSIG for 4 minutes through a downstream throttling device for reverse pre-blowing; mixing alkaline water-based concentrated cleaning agent with deionized water at a volume ratio of 1:5 and heating to 80°C to form a cleaning solution; installing an ultrasonic generator at the bottom of the oil cooler, so that the air passage of the oil cooler and the ultrasonic generator together form a sealed container, injecting the cleaning solution from the top inlet of the oil cooler, and simultaneously turning on the ultrasonic generator for soaking and cleaning for 15 minutes; draining the cleaning solution and removing the ultrasonic generator; introducing deionized water from the bottom outlet of the oil cooler in the opposite direction to the working airflow, and adjusting the water pressure to 20 PSIG~40 PSIG through a downstream throttling device for 5 minutes for reverse rinsing; replacing the deionized water and introducing it from the oil cooler... Deionized water is introduced through the top inlet of the oil cooler in the direction of the working airflow, and the water pressure is adjusted to 20 PSIG~40 PSIG through the downstream throttling device and maintained for 5 minutes for forward flushing. The pH value of the discharged deionized water is checked. If the pH value is less than 8.5, compressed air is introduced through the top inlet of the oil cooler in the direction of the working airflow, and the air pressure is adjusted to 20 PSIG~40 PSIG through the downstream throttling device and maintained for 10 minutes for forward drying. If the pH value is greater than or equal to 8.5, deionized water is introduced through the bottom outlet of the oil cooler in the opposite direction of the working airflow, and the water pressure is adjusted to 20 PSIG~40 PSIG through the downstream throttling device and maintained for 5 minutes for reverse flushing. The deionized water is replaced by introducing deionized water through the top inlet of the oil cooler in the direction of the working airflow, and the water pressure is adjusted to 20 PSIG~40 PSIG through the downstream throttling device and maintained for 5 minutes for forward flushing until the pH value of the discharged deionized water is less than 8.5.

[0005] This application provides an on-wing cleaning method for the air passage of an aviation auxiliary power unit lubricating oil cooler. Through the coordinated operation of steps such as reverse pre-blowing, ultrasonic chemical soaking, forward and reverse pressurized flushing, pH closed-loop detection, and hot air drying, the method achieves efficient and thorough cleaning of the air passage without disassembling the aircraft and quantitative control of the cleaning quality.

[0006] Additional aspects and advantages of this application will become apparent in the following description or may be learned by practice of this application. Attached Figure Description

[0007] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1A flowchart of an on-wing cleaning method for the air path of an aviation auxiliary power unit lubricating oil cooler according to an embodiment of this application; Figure 2 This is a schematic flowchart of an on-wing cleaning method for the air path of an aviation auxiliary power unit lubricating oil cooler according to an embodiment of this application; Figure 3 This is one of the structural connection diagrams of the on-wing cleaning method for the air path of the lubricating oil cooler of an aircraft auxiliary power unit in one embodiment of this application; Figure 4 This is a second schematic diagram of the structural connection of the air path of the lubricating oil cooler of the aviation auxiliary power unit in one embodiment of this application; Figure 5 This is the third schematic diagram of the structural connection of the on-wing cleaning method for the air path of the lubricating oil cooler of the aviation auxiliary power unit in one embodiment of this application; Figure 6 This is the fourth schematic diagram of the structural connection of the air path of the lubricating oil cooler of the aviation auxiliary power unit in one embodiment of this application; Figure 7 This is a schematic diagram of the structure of the lubricating oil cooler and the ultrasonic generator in one embodiment of this application.

[0008] in, Figures 3 to 7 The correspondence between the reference numerals and component names in the attached drawings is as follows: 100 Ultrasonic generating device, 110 Ultrasonic generator, 120 Stainless steel cavity, 130 Silicone connector, 140 Fixing clamp, 150 Drain valve, 200 Lubricating oil cooler, 202 Bottom outlet, 204 Top inlet, 300 Throttling device, 400 Filter device, 500 Air booster pump, 600 Booster water pump, 700 Water tank. Detailed Implementation

[0009] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0010] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0011] The following reference Figures 1 to 7 This application describes an on-wing cleaning method for the air passage of an aviation auxiliary power unit lubricating oil cooler, according to some embodiments thereof.

[0012] like Figure 1As shown, one embodiment of this application provides a method for on-wing cleaning of the air passage of an aviation auxiliary power unit lubricating oil cooler, comprising the following steps: S1. Compressed air is introduced from the bottom outlet of the lubricating oil cooler air passage in the opposite direction to the working airflow, and the air passage pressure is maintained at 15PSIG~30PSIG through the downstream throttling device for 4 minutes to perform reverse pre-purge. S2. Mix alkaline water-based concentrated cleaning agent with deionized water at a volume ratio of 1:5 and heat to 80°C to form a cleaning solution. S3. Install an ultrasonic generator at the bottom of the lubricating oil cooler so that the air passage of the lubricating oil cooler and the ultrasonic generator together form a sealed container. Inject the cleaning fluid from the top inlet of the lubricating oil cooler and turn on the ultrasonic generator at the same time. Soak and clean for 15 minutes. S4. Drain the cleaning fluid and remove the ultrasonic generator; S5. From the bottom outlet of the lubricating oil cooler, introduce deionized water in the opposite direction to the working airflow, and adjust the water pressure to 20PSIG~40PSIG through the downstream throttling device, and keep it for 5 minutes to perform backflushing. S6. Replace with deionized water. Introduce deionized water from the top inlet of the lubricating oil cooler in the direction of the working airflow, and adjust the water pressure to 20 PSIG~40 PSIG through the downstream throttling device. Maintain for 5 minutes to perform a forward flush. S7. Detect the pH value of the deionized water discharged in step S6. If the pH value is less than 8.5, proceed to step S8. If the pH value is greater than or equal to 8.5, repeat the backwashing step in step S5 and the forward rinsing step in step S6 until the pH value of the discharged deionized water is less than 8.5. S8. Introduce compressed air from the top inlet of the lubricating oil cooler in the direction of working airflow, and adjust the air pressure to 20PSIG~40PSIG through the downstream throttling device, and maintain it for 10 minutes to perform forward drying.

[0013] Specifically, such as Figure 1As shown, in step S1, under normal operating conditions, air enters from the top inlet and exits from the bottom outlet. Reverse-flowing compressed air blows out loose dust, debris, and other large particles adhering to the air fins and inner walls of the channels, preventing them from being further pressed into the fins during forward airflow. The throttling device creates back pressure at the outlet side of the lubricating oil cooler, ensuring the compressed air is evenly distributed within the air path and fully contacts the gaps between the fins, thus improving purging efficiency. In step S2, the alkaline water-based concentrated cleaning agent effectively emulsifies and decomposes common organic contaminants such as oil stains and carbon deposits in the lubricating oil cooler's air path. Deionized water, free of metal ions, avoids introducing additional impurities during cleaning. Heating to 80°C significantly increases the chemical reactivity of the cleaning agent, reduces the viscosity of the oil stains, making them easier to emulsify and peel off. High temperature also enhances the cleaning effect of subsequent ultrasonic cavitation. In step S3, the bottom sealing device temporarily transforms the lubricating oil cooler's air path into a container capable of holding liquid, allowing the heated alkaline cleaning solution to completely immerse the air fins and channels. The cavitation effect generated by the ultrasonic generator produces countless tiny bubbles in the liquid. These bubbles rapidly form and collapse under the influence of the sound field, releasing powerful shock waves and micro-jets. These shock waves can penetrate deep into the micro-channels and bends of the fins, areas difficult to reach by mechanical cleaning, breaking up and peeling off stubborn dirt that has been softened and emulsified by the chemical cleaning solution, achieving a synergistic effect of chemical dissolution and physical removal. In step S4, the alkaline cleaning solution containing a large amount of suspended dirt after soaking and cleaning is discharged from the air path to prevent secondary contamination in subsequent rinsing steps. The ultrasonic generator is removed to restore the open state of the bottom outlet of the lubricating oil cooler so that deionized water can be introduced from the bottom outlet for reverse rinsing, and also to facilitate the connection of external rinsing pipelines. In step S5, pressurized deionized water is introduced in reverse from the bottom outlet, with the water flow direction consistent with the blowing direction in step S1. This allows the dirt fragments and residual cleaning solution that have been peeled off in step S3 but are still trapped inside the air path to be flushed out from the top inlet. The shearing and scouring forces generated by the pressurized water flow further remove loosely attached particles. The throttling device creates back pressure at the top inlet side, ensuring the water flow fully fills the entire air passage and effectively flushes all fin gaps. In step S6, replacing the water with fresh deionized water avoids secondary contamination from using contaminated flushing water. During forward flushing, the water flow direction is consistent with the normal operating airflow direction, effectively pushing any residual dirt from the reverse flushing outwards from the bottom outlet. Combining forward and reverse flushing, alternating the water flow direction, ensures that residues in all angles and blind spots within the air passage are effectively removed. In step S7, if alkaline cleaning fluid remains in the lubricating oil cooler air passage, once the APU is started, the residual alkaline substances may be carried into the lubricating oil system or enter the engine with the airflow, causing corrosion or contamination. pH value is a quantitative indicator of the acidity or alkalinity of a solution; when the pH value of the discharged water is less than 8.5, it indicates that there is no significant alkaline residue in the air passage.If the pH value remains high, it indicates insufficient rinsing. In this case, repeated reverse and forward rinsing is automatically triggered, forming a closed-loop feedback control until the acceptable standard is met. In step S8, after multiple water rinses, a certain amount of moisture will remain inside the air passage. If this moisture is not completely removed, the humid air during APU startup may affect combustion efficiency, and long-term moisture residue can lead to rust and corrosion of metal components. Filtered and dried compressed air is introduced in the forward direction, using a high-speed airflow to disperse and carry away the water film adhering to the fins and inner walls of the channels. Simultaneously, a throttling device maintains a certain back pressure to ensure uniform airflow distribution. This process continues for 10 minutes, which is sufficient to dry the inside of the air passage and restore the normal ventilation and heat dissipation capacity of the oil cooler.

[0014] Compared with existing technologies, the on-wing cleaning method for the air path of the aviation auxiliary power unit (APU) lubricating oil cooler provided in this application has the following advantages: First, it achieves on-wing cleaning without disassembling the lubricating oil cooler. Throughout the cleaning process, the lubricating oil cooler remains installed on the aircraft, without the need to disassemble any lubricating oil lines or the APU itself. This completely avoids the lubricating oil leakage, environmental pollution, and cumbersome procedures of reinstallation and testing that are caused by disassembly in traditional off-site cleaning methods, saving maintenance time and reducing labor costs. Second, the combined use of ultrasonic waves and heated alkaline cleaning fluid ensures thorough cleaning, effectively removing stubborn dirt such as sintered sludge and carbon deposits that are difficult to remove with traditional circulating flushing, thus improving cleaning quality. Third, by detecting the pH value of the final discharged water, the cleaning is considered qualified only when the pH value is less than 8.5; otherwise, it automatically triggers repeated reverse and forward flushing until the standard is met, enhancing the safety and reliability of the cleaning process. Fourth, the use of alternating pressurized water flushing and hot air drying ensures that there is no residue or moisture in the air path, guaranteeing that the lubricating oil cooler can be put into use immediately after cleaning.

[0015] Specifically, an aircraft auxiliary power unit (APU) is a small aero gas turbine engine used to provide AC power and compressed air to the aircraft both on the ground and in the air. An oil cooler is used to dissipate heat from the APU's lubricating oil system, ensuring that the lubricating oil temperature remains within a specified range throughout APU operation. During use, blockages can easily occur in the air fins and channels of the oil cooler, leading to reduced cooling airflow, decreased heat dissipation performance, and consequently, increased lubricating oil temperature. In severe cases, this can cause a protective shutdown of the APU, affecting flight safety and operational efficiency. Currently, for on-wing APUs, when the oil cooler's air path is blocked, existing technology commonly employs the method of removing the oil cooler from the aircraft for cleaning. While this method achieves the cleaning purpose, it has significant drawbacks: First, the disassembly and reassembly process is complex, requiring the removal of multiple pipes and accessories, consuming a significant amount of maintenance time. Furthermore, the disassembly and reassembly process is prone to oil leakage, polluting the environment, and carries the risk of insufficient lubricating oil volume after leakage. Secondly, after the oil cooler is reinstalled, a ground test of the APU is required to check the installation status and the sealing of the oil system. This procedure is cumbersome and complex, further increasing the maintenance cycle and cost. Thirdly, off-site cleaning requires sending the oil cooler to a professional cleaning facility, resulting in long transportation and waiting times, hindering rapid response to line maintenance needs and affecting aircraft availability. Fourthly, existing off-site cleaning methods mostly use simple circulating rinsing or soaking, which is insufficient to thoroughly remove stubborn dirt deep within the air passage fins. The cleaning effect is unstable, often requiring repeated disassembly and reassembly for cleaning. Therefore, there is an urgent need for an on-wing cleaning method that can achieve efficient and thorough air passage cleaning without removing the oil cooler, and that allows for quantitative control of the cleaning process to ensure no residue damages the APU system. This would improve APU maintenance efficiency, reduce operating costs, and ensure flight safety.

[0016] To address the shortcomings of existing technologies, such as Figure 1As shown, this application provides an on-wing cleaning method for the air passage of an aviation auxiliary power unit lubricating oil cooler. Through the coordinated use of steps such as reverse pre-blowing, ultrasonic chemical immersion, forward and reverse pressurized flushing, pH closed-loop detection, and hot air drying, efficient and thorough cleaning of the air passage without disassembly is achieved, along with quality control of the cleaning quality. Specifically, in the air passage pre-treatment scenario, compressed air is reverse-flowed from the bottom outlet of the lubricating oil cooler and pressurized to blow away loose dust, debris, and other large particulate impurities from the air passage. This prevents the blockage from being further pushed into the fins during forward flow, creating favorable conditions for subsequent chemical cleaning. In the scenario of deep removal of stubborn dirt, an alkaline cleaning solution heated to 80°C is injected into the lubricating oil cooler air passage, while simultaneously activating the ultrasonic generator, creating a sealed container for immersion cleaning of the air passage and the device. The cavitation effect generated by ultrasound can penetrate deep into the micro-channels and dead corners of the air path fins, breaking down and peeling away stubborn dirt such as oil stains and carbon deposits softened and emulsified by chemical cleaning fluid. This achieves a synergistic effect of chemical dissolution and physical stripping, solving the problem that traditional flushing methods struggle to remove deep-seated deposits. In a scenario where no cleaning fluid residue is ensured, deionized water is pressurized and flushed in reverse and then forward directions, alternating the water flow direction to thoroughly flush away the detached dirt and residual cleaning fluid from the air path. The pH value of the discharged water is used to quantitatively determine the cleaning endpoint. If the pH value is greater than or equal to 8.5, repeated flushing is automatically triggered until the effluent is neutral, fundamentally eliminating the risk of corrosion from alkaline cleaning fluid residue on the lubricating oil system and ensuring a controllable and verifiable cleaning process. If the pH value is less than 8.5, filtered and dried compressed air is introduced in the forward direction to thoroughly dry the inside of the air path, preventing moisture residue from causing corrosion or affecting airflow during APU restart, ensuring that the lubricating oil cooler can be put into immediate use after cleaning. Throughout the cleaning process, the oil cooler remains installed on the aircraft, i.e., in the wing position, without the need to disassemble any oil lines or the APU itself, completely avoiding the drawbacks of traditional off-site cleaning such as oil leakage, cumbersome testing, and long cycles.

[0017] In some embodiments, optionally, such as Figure 1 As shown, steps S1 to S8 are all performed while the lubricating oil cooler is still installed on the aircraft.

[0018] Specifically, such as Figure 1As shown, the entire cleaning process does not require removing the oil cooler from the auxiliary power unit, nor does it require disconnecting the oil lines from the aircraft system. All operations are performed via detachable connections between external equipment and the oil cooler's air inlet and bottom outlet, while the mechanical installation of the oil cooler and the oil line connections remain unchanged. Reverse pre-blowing, ultrasonic immersion cleaning, forward and reverse rinsing, and hot air drying are all completed with the oil cooler installed in its original position. This completely avoids the significant time spent disassembling the oil cooler in traditional off-site cleaning methods, the environmental pollution caused by oil leakage during disassembly, and the risk of oil loss. It also eliminates the cumbersome procedure of ground testing after reinstallation to check the installation status, significantly reducing APU downtime for maintenance, lowering repair costs, and minimizing secondary risks such as damage to pipe joints or seal failure due to frequent disassembly.

[0019] In some embodiments, optionally, such as Figure 1 As shown, in step S2, the alkaline water-based concentrated cleaning agent is a water-based alkaline concentrated compound, and its 1% aqueous solution has a pH value of not less than 11 at 20°C.

[0020] Specifically, such as Figure 1 As shown, stubborn contaminants in the air passage of the lubricating oil cooler mainly include carbon deposits that have undergone high-temperature oxidation and deterioration, sintered sludge, and colloidal complexes formed by mixing with dust. These contaminants mostly contain acidic functional groups or ester structures. In a strongly alkaline environment, alkaline cleaning solutions can decompose grease-like contaminants into water-soluble fatty acid salts through saponification. Simultaneously, hydrolysis breaks down the high molecular weight chains in the carbon deposits and colloidal complexes, reducing their molecular weight and increasing their polarity, thus facilitating emulsification and dispersion in water. If the pH value is below 11, the alkali concentration is insufficient to effectively saponify or hydrolyze stubborn contaminants, and the cleaning effect will significantly decrease. This application limits the cleaning agent to a highly alkaline, water-based alkaline concentrated compound, providing a cleaning basis for the subsequent ultrasonic chemical cleaning step. This allows the cleaning solution to fully soften and decompose stubborn contaminants in the air passage, and then, combined with the cavitation effect of ultrasound, completely remove them, thereby achieving efficient and deep cleaning of the lubricating oil cooler's air passage.

[0021] In some embodiments, optionally, such as Figure 1 As shown, in step S3, the operating frequency of the ultrasonic generator is 20kHz~40kHz.

[0022] Specifically, such as Figure 1As shown, by limiting the operating frequency of the ultrasonic generator to the range of 20kHz to 40kHz, sufficient cavitation energy is ensured to effectively remove sintered sludge and carbon deposits on the air passage fins of the lubricating oil cooler, while avoiding damage to the thin-walled structure of the fins that may be caused by excessively low frequencies. At the same time, cleaning efficiency and safety are taken into account, ensuring that the ultrasonic waves can act evenly on the micro-channels and dead corners of various parts of the air passage, achieving efficient and non-destructive deep cleaning.

[0023] In some embodiments, optionally, such as Figure 1 As shown, in step S3, the temperature of the cleaning solution is maintained between 78°C and 82°C throughout the entire soaking and cleaning process.

[0024] Specifically, such as Figure 1 As shown, the temperature of the cleaning solution significantly affects the chemical cleaning reaction rate, the physical state of the dirt, and the ultrasonic cavitation effect. If the temperature is below 78℃, the chemical cleaning rate decreases and the dirt is not sufficiently softened; if the temperature is above 82℃, the cavitation effect weakens and the cleaning solution evaporates more rapidly, which may affect the cleaning effect and operational safety. By strictly limiting the temperature within this range through constant temperature control, the stability and consistency of the cleaning performance are ensured throughout the immersion cleaning process, significantly improving the ability to remove stubborn dirt from the air passage of the lubricating oil cooler.

[0025] In some embodiments, optionally, such as Figure 1 As shown, in steps S5 and S6, reverse flushing and forward flushing are performed sequentially to alternately change the flow direction of deionized water in the gas path.

[0026] Specifically, such as Figure 1 As shown, the internal structure of the air passage of the lubricating oil cooler is complex, containing multiple layers of fins, narrow channels, and bends. Dirt and residual cleaning fluid can easily accumulate in certain dead corners or on the backflow surface. If only unidirectional flushing is used, the water flow will follow the path of least resistance, making it difficult to effectively flush out dirt in some areas. This application first performs reverse flushing, with deionized water entering from the bottom outlet and exiting from the top inlet, the water flow direction being consistent with the reverse pre-blowing direction. This allows the dirt fragments detached after ultrasonic soaking cleaning to be flushed out of the air passage in the reverse direction. Then, forward flushing is performed, with deionized water entering from the top inlet and exiting from the bottom outlet, the water flow direction being consistent with the normal operating airflow direction. This allows any residue that might have been missed during reverse flushing to be pushed out from the forward direction. The two flushing directions are performed alternately, creating a flow field with alternating directions for the deionized water within the air passage. This continuously changes the pressure distribution and flow direction of the water flow, effectively flushing the walls and fin gaps at various angles within the air passage, overcoming the dead corner problem of unidirectional flushing and improving flushing efficiency.

[0027] In some embodiments, optionally, such as Figure 1As shown, in step S7, the pH value of the discharged deionized water is detected using a portable pH meter or an online pH sensor, and the detection point is the bottom outlet drain of the lubricating oil cooler.

[0028] Specifically, such as Figure 1 As shown, after the forward flushing is completed, the discharged deionized water, carrying trace amounts of residual alkaline cleaning fluid from the gas path, flows out from the bottom outlet of the lubricating oil cooler. This outlet is the final drainage point of the entire gas path flushing process. Measuring the pH value at this point directly and accurately reflects the concentration level of residual cleaning fluid inside the gas path. Portable pH meters are suitable for on-site manual sampling and testing, offering flexibility and low cost; online pH sensors can continuously monitor the changing trend of the drainage pH value in real time, facilitating automated control. Using a pH meter or pH sensor for detection allows for quantified output of pH values. By setting the detection point at the bottom outlet drainage point, it ensures that the measured water sample flows completely through the entire gas path channel, achieving a quantitative determination of the cleaning endpoint and completely eliminating safety hazards caused by alkaline residue.

[0029] In some embodiments, optionally, such as Figure 1 As shown, in step S7, the pH value of the discharged deionized water is detected to determine whether there is any alkaline cleaning fluid remaining in the air path of the lubricating oil cooler. When the pH value is greater than or equal to 8.5, it is determined that there is cleaning fluid residue, and repeated flushing is triggered to ensure that there is no alkaline substance residue in the air path of the lubricating oil cooler.

[0030] Specifically, such as Figure 1 As shown, when the detected pH value is greater than or equal to 8.5, it indicates that there is still significant alkaline cleaning fluid remaining in the gas path. At this time, the reverse flushing and forward flushing are automatically triggered repeatedly until the pH value drops below 8.5. This fundamentally eliminates the safety hazard of cleaning fluid residue, realizes the accurate determination of the cleaning endpoint, ensures that the lubricating oil cooler gas path reaches a safe state without alkaline residue after cleaning, and ensures the safety and reliability of the APU's subsequent operation.

[0031] In some embodiments, optionally, such as Figure 1 As shown, in step S8, the compressed air undergoes filtration and drying.

[0032] Specifically, such as Figure 1 As shown, by setting up filtration and drying processes, the compressed air entering the oil cooler's air passage is ensured to be clean and dry. During the forward drying process, the clean and dry compressed air can efficiently disperse and carry away any residual water film within the air passage, without introducing new solid particles, oil, or moisture contaminants. This ensures that the inside of the oil cooler's air passage is dry and clean after cleaning, allowing it to immediately restore normal cooling and heat dissipation functions and avoiding the risk of secondary contamination and corrosion.

[0033] In some embodiments, optionally, such as Figure 1 and Figure 7 As shown, in step S3, the ultrasonic generating device includes: an ultrasonic generator; a stainless steel cavity, the ultrasonic generator being fixedly installed at the bottom of the stainless steel cavity; a silicone connector, the lower end of which is sealed to the upper opening of the stainless steel cavity; and a fixing clamp, which seals the upper end of the silicone connector to the bottom outlet of the lubricating oil cooler; wherein, the stainless steel cavity is also provided with a drain valve for draining the cleaning fluid.

[0034] Specifically, such as Figure 7 As shown, the ultrasonic generator includes an ultrasonic generator, a stainless steel cavity, a silicone connector, and a fixing clamp. The ultrasonic generator is fixedly mounted at the bottom of the stainless steel cavity. The lower end of the silicone connector is sealed to the upper opening of the stainless steel cavity. The fixing clamp seals the upper end of the silicone connector to the bottom outlet of the oil cooler. A drain valve is also provided on the stainless steel cavity for draining the cleaning fluid. Through the coordinated operation of the stainless steel cavity, silicone connector, and fixing clamp, a reliable seal can be quickly formed at the bottom outlet of the oil cooler while it is still installed on the aircraft. This temporarily transforms the air path of the oil cooler into a sealed container for the cleaning fluid, providing the necessary conditions for ultrasonic chemical immersion cleaning. Simultaneously, this structure facilitates quick disassembly and installation, meeting the operational convenience requirements of on-wing cleaning, and possesses good corrosion resistance and sealing reliability, ensuring the safety and stability of the cleaning process.

[0035] In practical applications, this application provides an on-wing cleaning method for the air passage of an aviation auxiliary power unit's lubricating oil cooler. This method enables efficient and thorough cleaning of the air passage without disassembling the lubricating oil cooler, and allows for control over the cleaning quality. Figure 2 As shown, the specific implementation method is as follows: Step 1: Through the bottom outlet of the lubricating oil cooler air passage, introduce compressed air into the lubricating oil cooler air passage in the opposite direction of the working airflow. Through the downstream throttling device, maintain the air passage pressure at 15PSIG~30PSIG for 4 minutes. Step 2: Mix the alkaline water-based concentrated cleaning agent with deionized water at a volume ratio of 1:5 and heat to 80℃; Step 3: Install an ultrasonic generator at the bottom of the oil cooler so that the air passage of the oil cooler and the ultrasonic generator together form a sealed container. Inject the cleaning fluid from the top inlet of the oil cooler and turn on the ultrasonic generator at the same time. Soak and clean for 15 minutes. Step 4: Drain the cleaning fluid, remove the ultrasonic generator, and then introduce deionized water from the bottom outlet of the lubricating oil cooler in the opposite direction to the working airflow. Adjust the water pressure to 20 PSIG~40 PSIG through the downstream throttling device and maintain it for 5 minutes. Step 5: Replace with deionized water. Introduce deionized water from the top inlet of the lubricating oil cooler in the direction of the working airflow, and adjust the water pressure to 20 PSIG~40 PSIG through the downstream throttling device, and maintain for 5 minutes. Step Six: Check the pH value of the discharged deionized water to determine if it is less than 8.5. If the pH value is less than 8.5, introduce compressed air from the top inlet of the oil cooler in the direction of the working airflow, and adjust the air pressure to 20 PSIG~40 PSIG through the downstream throttling device, maintaining this pressure for 10 minutes for forward drying. If the pH value is greater than or equal to 8.5, introduce deionized water from the bottom outlet of the oil cooler in the opposite direction of the working airflow, and adjust the water pressure to 20 PSIG~40 PSIG through the downstream throttling device, maintaining this pressure for 5 minutes. Replace the deionized water by introducing it from the top inlet of the oil cooler in the direction of the working airflow, and adjusting the water pressure to 20 PSIG~40 PSIG through the downstream throttling device, maintaining this pressure for 5 minutes.

[0036] The alkaline water-based concentrated cleaning agent is specifically TURCO5948 cleaning agent, the throttling device is specifically a throttling valve, and the water pressure is approximately 6.895 kPa per PSIG.

[0037] Specifically, such as Figure 7 As shown, the ultrasonic generator 100, from bottom to top, includes an ultrasonic generator 110, a stainless steel cavity 120, a silicone connector 130, and a fixing clamp 140. The ultrasonic generator 110 is fixedly installed at the bottom of the stainless steel cavity 120. The lower end of the silicone connector 130 is sealed to the upper opening of the stainless steel cavity 120. The fixing clamp 140 seals the upper end of the silicone connector 130 to the bottom outlet 202 of the lubricating oil cooler 200. A drain valve 150 is provided on the stainless steel cavity 120 for draining cleaning fluid.

[0038] In specific implementation, such as Figure 3 As shown, Figure 3 This is a schematic diagram of the structural connection when performing step one of the air circuit cleaning method of the lubricating oil cooler 200 of the aviation auxiliary power unit. The bottom outlet 202 of the lubricating oil cooler 200 is connected to the air booster pump 500, and the top inlet 204 of the lubricating oil cooler 200 is connected to the throttling device 300. The throttling device 300 is connected to the filter device 400.

[0039] In specific implementation, such as Figure 4 As shown, Figure 4 This is a structural connection diagram of step four of the air circuit cleaning method for the air circuit of the aviation auxiliary power unit lubricating oil cooler 200. The bottom outlet 202 of the lubricating oil cooler 200 is connected to the booster water pump 600. The top inlet 204 of the lubricating oil cooler 200 is connected to the throttling device 300. The throttling device 300 is connected to the filter device 400. The filter device 400 is connected to the water tank 700. The water tank 700 is connected to the booster water pump 600.

[0040] In specific implementation, such as Figure 5 As shown, Figure 5 This is a structural connection diagram of step five in the air circuit cleaning method of the aviation auxiliary power unit lubricating oil cooler 200. The top inlet 204 of the lubricating oil cooler 200 is connected to the booster water pump 600. The bottom outlet 202 of the lubricating oil cooler 200 is connected to the throttling device 300. The throttling device 300 is connected to the filter device 400. The filter device 400 is connected to the water tank 700. The water tank 700 is connected to the booster water pump 600.

[0041] In specific implementation, such as Figure 6 As shown, Figure 6 This is a structural connection diagram of step six of the air circuit cleaning method for the air circuit of the aviation auxiliary power unit oil cooler 200. The top inlet 204 of the oil cooler 200 is connected to the air booster pump 500, and the bottom outlet 202 of the oil cooler 200 is connected to the throttling device 300. The throttling device 300 is connected to the filter device 400.

[0042] In the description of this application, the term "multiple" refers to two or more. Unless otherwise expressly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. The terms "connection," "installation," "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0043] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0044] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for on-wing cleaning of the air passage of an aviation auxiliary power unit lubricating oil cooler, characterized in that, Includes the following steps: S1. Compressed air is introduced from the bottom outlet of the lubricating oil cooler air passage in the opposite direction to the working airflow, and the air passage pressure is maintained at 15PSIG~30PSIG through the downstream throttling device for 4 minutes to perform reverse pre-purge. S2. Mix alkaline water-based concentrated cleaning agent with deionized water at a volume ratio of 1:5 and heat to 80°C to form a cleaning solution. S3. Install an ultrasonic generator at the bottom of the lubricating oil cooler, so that the air passage of the lubricating oil cooler and the ultrasonic generator together form a sealed container. Inject the cleaning fluid from the top inlet of the lubricating oil cooler, and at the same time turn on the ultrasonic generator. Soak and clean for 15 minutes. S4. Drain the cleaning fluid and remove the ultrasonic generator; S5. Deionized water is introduced from the bottom outlet of the lubricating oil cooler in the opposite direction to the working airflow, and the water pressure is adjusted to 20PSIG~40PSIG through the downstream throttling device and maintained for 5 minutes to perform backflushing. S6. Replace with deionized water. Introduce deionized water from the top inlet of the lubricating oil cooler in the direction of working airflow, and adjust the water pressure to 20 PSIG~40 PSIG through the downstream throttling device. Maintain for 5 minutes to perform a forward flush. S7. Detect the pH value of the deionized water discharged in step S6. If the pH value is less than 8.5, proceed to step S8. If the pH value is greater than or equal to 8.5, repeat the backwashing step in step S5 and the forward rinsing step in step S6 until the pH value of the discharged deionized water is less than 8.

5. S8. Compressed air is introduced from the top inlet of the lubricating oil cooler in the direction of working airflow, and the air pressure is adjusted to 20PSIG~40PSIG through the downstream throttling device and maintained for 10 minutes to perform forward drying.

2. The on-wing cleaning method for the air path of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, Steps S1 to S8 are performed while the lubricating oil cooler is still installed on the aircraft.

3. The on-wing cleaning method for the air path of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S2, the alkaline water-based concentrated cleaning agent is a water-based alkaline concentrated compound, and its 1% aqueous solution has a pH value of not less than 11 at 20°C.

4. The on-wing cleaning method for the air path of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S3, the operating frequency of the ultrasonic generator is 20kHz~40kHz.

5. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S3, the temperature of the cleaning solution is maintained between 78°C and 82°C throughout the entire soaking and cleaning process.

6. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In steps S5 and S6, reverse flushing and forward flushing are performed sequentially to alternately change the flow direction of deionized water in the gas path.

7. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S7, the pH value of the discharged deionized water is detected using a portable pH meter or an online pH sensor, and the detection point is the bottom outlet drain of the lubricating oil cooler.

8. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 7, characterized in that, In step S7, the pH value of the discharged deionized water is detected to determine whether there is any alkaline cleaning fluid remaining in the air path of the lubricating oil cooler. When the pH value is greater than or equal to 8.5, it is determined that there is cleaning fluid residue, and repeated flushing is triggered to ensure that there is no alkaline substance residue in the air path of the lubricating oil cooler.

9. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S8, the compressed air undergoes filtration and drying.

10. The on-wing cleaning method for the air passage of the lubricating oil cooler of an aircraft auxiliary power unit according to claim 1, characterized in that, In step S3, the ultrasonic generator includes: Ultrasonic generator; A stainless steel cavity, wherein the ultrasonic generator is fixedly installed at the bottom of the stainless steel cavity; A silicone connector, the lower end of which is sealed to the upper opening of the stainless steel cavity; A fixing clamp is used to seal and connect the upper end of the silicone connector to the bottom outlet end of the lubricating oil cooler. The stainless steel cavity is also equipped with a drain valve for discharging cleaning fluid.

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