Low-temperature starting four-stroke unmanned aerial vehicle engine lubricating oil and preparation method thereof

Abstract

The application relates to the technical field of lubricating oil, and discloses a low-temperature starting type four-stroke unmanned aerial vehicle engine lubricating oil and a preparation method thereof, the preparation method is as follows: PAO4 base oil, alkyl naphthalene AN30 and a viscosity index improver are added into a blending kettle, the temperature is raised to 55-65 DEG C, and stirring is carried out for 20-30 min, then modified phosphate, modified hexagonal boron nitride, polyisobutylene succinimide, a composite antioxidant and a defoaming agent are sequentially added, ultrasonic stirring is carried out at 70-80 DEG C for 1-2 h, the mixture is filtered through a 180-200 mesh precision filter screen, and cooling is carried out, so that the low-temperature starting type four-stroke unmanned aerial vehicle engine lubricating oil is obtained. The low-temperature starting type four-stroke unmanned aerial vehicle engine lubricating oil prepared by the application has good low-temperature starting performance, high-temperature high-shear performance and extreme pressure anti-wear performance.

Description

Technical Field

[0001] This invention relates to the field of lubricating oil technology, specifically to a low-temperature start-up type four-stroke unmanned aerial vehicle engine lubricating oil and its preparation method. Background Technology

[0002] As the application of drones in border patrol, power line inspection, and emergency rescue continues to expand, their operational scenarios are gradually extending to high-altitude and extremely cold regions. Four-stroke gasoline engines, with their high thermal efficiency and fuel economy, have become the mainstream power source for medium and large industrial drones. However, when these engines start in low-temperature environments, the viscosity of the lubricating oil rises sharply, increasing crankshaft rotation resistance and often leading to starting difficulties or even failure to start. Furthermore, during long-duration high-altitude flights, the engine operates under high-temperature and low-pressure conditions, placing stringent demands on the high-temperature shear resistance and oxidation resistance of the lubricating oil. Currently, most drone lubricating oils directly utilize motorcycle engine oils and general-purpose small aircraft engine lubricating oil systems, simply compounding viscosity index improvers and conventional anti-wear additives, making it difficult to simultaneously meet the two core requirements of ultra-low temperature cold starts and high-altitude, high-temperature, long-term lubrication. Therefore, avoiding this phenomenon is key to solving the problem. For example, patent application CN120290245A discloses a lubricating oil composition for a four-stroke UAV engine. The lubricating oil composition for a four-stroke UAV engine has excellent anti-wear and anti-oxidation properties, but the overall formula is not optimized for the specific working conditions of UAVs, such as sudden changes in high and low temperatures and frequent start-stop. The oil has insufficient low-temperature fluidity and high starting resistance in low-temperature environments, which cannot meet the lubrication needs of UAVs for long-term stable operation in complex environments. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a low-temperature start-up type four-stroke UAV engine lubricating oil and its preparation method. The low-temperature start-up type four-stroke UAV engine lubricating oil prepared by the present invention has good low-temperature start-up performance, high-temperature high-shear performance and extreme pressure anti-wear performance.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a low-temperature start-up type four-stroke unmanned aerial vehicle engine lubricating oil, comprising the following weight components: 70-80 parts by weight of PAO4 base oil, 10-15 parts by weight of alkyl naphthalene AN30, 4-6 parts by weight of viscosity index improver, 0.5-1 parts by weight of modified phosphate, 0.3-0.5 parts by weight of modified hexagonal boron nitride, 3-5 parts by weight of polyisobutylene succinimide, 1-2 parts by weight of composite antioxidant, and 0.01-0.02 parts by weight of defoamer.

[0005] Furthermore, the method for preparing the modified phosphate is as follows:

[0006] Step 1: Add bis(trimethylolpropane), phosphorus oxychloride and 1,4-dioxane to the reactor, mix well, and react at 50-60℃ for 4-6 hours. After the reaction is completed, vacuum distill and dry to obtain bis(trimethylolpropane) diphosphorus chloride.

[0007] Step 2: Dissolve bis(trimethylolpropane) diphosphate chloride in 1,4-dioxane, then add deionized water dropwise to the solution. After the addition is complete, react at 70-80℃ for 1-2 hours. After the reaction is complete, distill under reduced pressure and dry to obtain bis(trimethylolpropane) diphosphate.

[0008] Step 3: Dissolve bis(trimethylolpropane) phosphate in 1,4-dioxane, then add octadecylamine to the solution, stir and mix, and react at 60-65℃ for 3-4 hours. After the reaction is complete, vacuum distill, wash and dry to obtain the modified phosphate.

[0009] Furthermore, in step one, the ratio of the amounts of bis(trimethylolpropane), phosphorus oxychloride, and 1,4-dioxane is 2.5-2.6g:3.8-3.9g:5-8mL.

[0010] Furthermore, in step two, the ratio of bis(trimethylolpropane) diphosphine chloride, 1,4-dioxane, and deionized water is 4-4.1g:2-3mL:0.5-0.6g.

[0011] Furthermore, in step three, the ratio of bis(trimethylolpropane) phosphate, 1,4-dioxane, and octadecylamine is 3.3-3.4g:8-10mL:4.5-4.6g.

[0012] Furthermore, the method for preparing the modified hexagonal boron nitride is as follows:

[0013] S1: Isopropanol and deionized water are added to the reactor and mixed to obtain a solution. Hexagonal boron nitride is added to the solution and ultrasonically treated for 1-1.5 hours. Then, the mixed solution is ultrasonically exfoliated using an ultrasonic cleaner for 10-12 hours. After the reaction is completed, the solution is centrifuged at 4500-5000 rpm for 30-40 minutes. The supernatant obtained after centrifugation is vacuum filtered and vacuum dried at 90-100℃ for 12-14 hours to obtain hydroxylated hexagonal boron nitride.

[0014] S2: Add 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to anhydrous dichloromethane solvent, and stir continuously to form a uniform reaction suspension. Then, add 3-aminopropyltriethoxysilane dropwise. After the addition is complete, stir the reaction at 30-40℃ for 12-16 h. After the reaction is complete, filter, collect the filtrate and evaporate it under reduced pressure to dry it, and obtain the phenylboronic acid coupling agent.

[0015] S3: Add 120-150 mL of ethanol and 40-50 mL of deionized water to the reactor to prepare a solvent. Add 0.15-0.2 g of hydroxylated hexagonal boron nitride to the solvent and sonicate for 1-2 h. Then dissolve 0.7-0.8 g of phenylboronic acid coupling agent in anhydrous ethanol and add it dropwise to the reactor with stirring. After the addition is complete, stir the reaction at 80-90℃ for 20-24 h. After the reaction is complete, cool to room temperature, filter, wash and dry to obtain modified hexagonal boron nitride.

[0016] Furthermore, the ratio of isopropanol, deionized water, and hexagonal boron nitride in S1 is 120-150mL:120-150mL:1.3-1.5g.

[0017] Further, the ratio of anhydrous dichloromethane, 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and 3-aminopropyltriethoxysilane in S2 is 30-40 mL: 1.6-1.7 g: 2-2.1 g: 1.1-1.2 g: 2.3-2.4 g.

[0018] Furthermore, the composite antioxidant is composed of 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine in a mass ratio of 1:1 to 1:2.

[0019] Furthermore, the preparation method of the low-temperature start-up type four-stroke UAV engine lubricating oil is as follows: PAO4 base oil, alkyl naphthalene AN30, and viscosity index improver are added to a mixing tank, heated to 55-65℃, and stirred for 20-30 minutes. Then, modified phosphate, modified hexagonal boron nitride, polyisobutylene succinimide, composite antioxidant, and defoamer are added sequentially. The mixture is then ultrasonically stirred at 70-80℃ for 1-2 hours. The mixture is filtered through a 180-200 mesh precision filter and cooled to obtain the low-temperature start-up type four-stroke UAV engine lubricating oil.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] This invention constructs a binary base oil system by compounding PAO4 base oil with alkyl naphthalene AN30. The polar properties of alkyl naphthalene AN30 disrupt the ordered crystallization tendency of PAO4 molecules at low temperatures, significantly improving the oil's fluidity in extremely cold environments and endowing the lubricant with excellent low-temperature starting performance, ensuring rapid and reliable starting of UAVs in extreme cold conditions. Modified phosphates are prepared by neutralizing bis(trimethylolpropane) diphosphate with octadecylamine, overcoming the defect of acidic intermediates easily corroding the friction pair surface. This process forms a dense chemical protective film on the metal surface, while the long chain of octadecylamine provides specific polar physical adsorption and steric hindrance effects. Hexagonal boron nitride modified with phenylboronic acid coupling agent utilizes the anchoring effect of phenylboronic acid groups on the metal surface, enabling boron nitride nanosheets to spread efficiently on the metal friction interface, forming a stable double-layer lubricating film. The synergistic effect of these two components enhances the extreme pressure anti-wear performance of the lubricant. A synergistic antioxidant system combining 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine is adopted, which can slow down the rate of oil oxidation and deterioration at high temperatures, inhibit the formation of sludge and carbon deposits, and ensure the clean operation of UAV engines during long-term continuous flight. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The reagents used in the following specific embodiments are of analytical grade. Additionally:

[0024] PAO4 base oil: Brand is FOX, model is PAO4, manufacturer is Shanghai FOX Chemical Technology Co., Ltd.;

[0025] Alkyl naphthalene AN30: Manufacturer is Shanghai Nake Lubrication Technology Co., Ltd.;

[0026] Viscosity index improver: HSD type viscosity index improver SV261, manufactured by Locke Chemical (Shenzhen) Co., Ltd.

[0027] Hexagonal boron nitride: purity 99%, manufacturer is Beijing Huawirui Chemical Co., Ltd.;

[0028] Defoamer: Organosilicon defoamer, model ZY-1022, manufactured by Shanghai Ziyi Chemical Co., Ltd.

[0029] Example 1

[0030] (1) Add 2.5g of bis(trimethylolpropane), 3.8g of phosphorus oxychloride and 5mL of 1,4-dioxane to the reactor, mix well, and react at 50°C for 4h. After the reaction is completed, vacuum distill and dry to obtain bis(trimethylolpropane) diphosphorus chloride.

[0031] (2) Dissolve 4g of bis(trimethylolpropane) diphosphate chloride in 2mL of 1,4-dioxane, then add 0.5g of deionized water dropwise to the solution. After the addition is complete, react at 70℃ for 1h. After the reaction is complete, distill under reduced pressure and dry to obtain bis(trimethylolpropane) diphosphate.

[0032] (3) Dissolve 3.3g of bis(trimethylolpropane) diphosphate in 8mL of 1,4-dioxane, then add 4.5g of octadecylamine to the solution, stir and mix, react at 60℃ for 3h, after the reaction is completed, vacuum distill, wash and dry to obtain modified phosphate;

[0033] (4) Add 120 mL of isopropanol and 120 mL of deionized water to the reactor, mix to prepare a solution, add 1.3 g of hexagonal boron nitride, sonicate for 1 h, and then use an ultrasonic cleaner to sonicate the mixed solution for 10 h. After the reaction is completed, centrifuge at 4500 rpm for 30 min, vacuum filter the supernatant obtained after centrifugation, and vacuum dry at 90 °C for 12 h to obtain hydroxylated hexagonal boron nitride.

[0034] (5) Add 1.6 g of 4-carboxyphenylboronic acid, 2 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.1 g of N-hydroxysuccinimide to 30 mL of anhydrous dichloromethane solvent, and stir continuously to form a uniform reaction suspension. Then add 2.3 g of 3-aminopropyltriethoxysilane dropwise. After the addition is complete, stir the reaction at 30 °C for 12 h. After the reaction is complete, filter, collect the filtrate and evaporate under reduced pressure to dry, and obtain phenylboronic acid coupling agent.

[0035] (6) Add 120 mL of ethanol and 40 mL of deionized water to the reactor and mix to prepare a solvent. Add 0.15 g of hydroxylated hexagonal boron nitride to the solvent and sonicate for 1 h. Then dissolve 0.7 g of phenylboronic acid coupling agent in anhydrous ethanol and add it dropwise to the reactor under stirring. After the addition is complete, stir the reaction at 80 °C for 20 h. After the reaction is complete, cool to room temperature, filter, wash and dry to obtain modified hexagonal boron nitride.

[0036] (7) Add 70 parts by weight of PAO4 base oil, 10 parts by weight of alkyl naphthalene AN30, and 4 parts by weight of viscosity index improver to a mixing vessel, heat to 55°C, stir for 20 min, and then add 0.5 parts by weight of modified phosphate, 0.3 parts by weight of modified hexagonal boron nitride, 3 parts by weight of polyisobutylene succinimide, 1 part by weight of composite antioxidant, and 0.01 parts by weight of defoamer in sequence. Then, ultrasonically stir at 70°C for 1 h, filter the mixture through a 180-mesh precision filter, and cool to obtain low-temperature start-up type four-stroke UAV engine lubricating oil.

[0037] Furthermore, the composite antioxidant is composed of 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine in a mass ratio of 1:1.

[0038] Example 2

[0039] (1) Add 2.6g of bis(trimethylolpropane), 3.9g of phosphorus oxychloride and 8mL of 1,4-dioxane to the reactor, mix well, and react at 60℃ for 6h. After the reaction is completed, vacuum distill and dry to obtain bis(trimethylolpropane) diphosphorus chloride.

[0040] (2) Dissolve 4.1 g of bis(trimethylolpropane) diphosphate chloride in 3 mL of 1,4-dioxane, and then add 0.6 g of deionized water dropwise to the solution. After the addition is complete, react at 80 °C for 2 h. After the reaction is complete, distill under reduced pressure and dry to obtain bis(trimethylolpropane) diphosphate.

[0041] (3) Dissolve 3.4 g of bis(trimethylolpropane) diphosphate in 10 mL of 1,4-dioxane, then add 4.6 g of octadecylamine to the solution, stir and mix, and react at 65 °C for 4 h. After the reaction is completed, vacuum distill, wash and dry to obtain modified phosphate.

[0042] (4) Add 150 mL of isopropanol and 150 mL of deionized water to the reactor, mix to prepare a solution, add 1.5 g of hexagonal boron nitride, sonicate for 1.5 h, and then use an ultrasonic cleaner to sonicate the mixed solution for 12 h. After the reaction is completed, centrifuge at 5000 rpm for 40 min, vacuum filter the supernatant obtained after centrifugation, and vacuum dry at 100 °C for 14 h to obtain hydroxylated hexagonal boron nitride.

[0043] (5) Add 1.7g of 4-carboxyphenylboronic acid, 2.1g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.2g of N-hydroxysuccinimide to 40mL of anhydrous dichloromethane solvent, and stir continuously to form a uniform reaction suspension. Then add 2.4g of 3-aminopropyltriethoxysilane dropwise. After the addition is complete, stir the reaction at 40℃ for 16h. After the reaction is completed, filter, collect the filtrate and evaporate under reduced pressure to dry, and obtain phenylboronic acid coupling agent.

[0044] (6) Add 150 mL of ethanol and 50 mL of deionized water to the reactor and mix to prepare a solvent. Add 0.2 g of hydroxylated hexagonal boron nitride to the solvent and sonicate for 2 h. Then dissolve 0.8 g of phenylboronic acid coupling agent in anhydrous ethanol and add it dropwise to the reactor under stirring. After the addition is complete, stir the reaction at 90 °C for 24 h. After the reaction is complete, cool to room temperature, filter, wash and dry to obtain modified hexagonal boron nitride.

[0045] (7) Add 80 parts by weight of PAO4 base oil, 15 parts by weight of alkyl naphthalene AN30, and 6 parts by weight of viscosity index improver to a mixing vessel, heat to 65°C, stir for 30 min, and then add 1 part by weight of modified phosphate, 0.5 parts by weight of modified hexagonal boron nitride, 5 parts by weight of polyisobutylene succinimide, 2 parts by weight of composite antioxidant, and 0.02 parts by weight of defoamer in sequence. Then, ultrasonically stir at 80°C for 2 h, filter the mixture through a 200-mesh precision filter, cool, and obtain low-temperature start-up type four-stroke UAV engine lubricating oil.

[0046] Furthermore, the composite antioxidant is composed of 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine in a mass ratio of 1:2.

[0047] Example 3

[0048] (1) Add 2.55g of bis(trimethylolpropane), 3.85g of phosphorus oxychloride and 6mL of 1,4-dioxane to the reactor, mix well, and react at 55℃ for 5h. After the reaction is completed, vacuum distill and dry to obtain bis(trimethylolpropane) diphosphorus chloride.

[0049] (2) Dissolve 4.05 g of bis(trimethylolpropane) diphosphate chloride in 2.5 mL of 1,4-dioxane, then add 0.55 g of deionized water dropwise to the solution. After the addition is complete, react at 75 °C for 1.5 h. After the reaction is complete, distill under reduced pressure and dry to obtain bis(trimethylolpropane) diphosphate.

[0050] (3) Dissolve 3.35g of bis(trimethylolpropane) diphosphate in 9mL of 1,4-dioxane, then add 4.55g of octadecylamine to the solution, stir and mix, and react at 62℃ for 3h. After the reaction is completed, vacuum distill, wash and dry to obtain modified phosphate.

[0051] (4) Add 140 mL of isopropanol and 140 mL of deionized water to the reactor, mix to prepare a solution, add 1.4 g of hexagonal boron nitride, sonicate for 1 h, and then use an ultrasonic cleaner to sonicate the mixed solution for 11 h. After the reaction is completed, centrifuge at 4500 rpm for 35 min, vacuum filter the supernatant obtained after centrifugation, and vacuum dry at 95 °C for 13 h to obtain hydroxylated hexagonal boron nitride.

[0052] (5) Add 1.65 g of 4-carboxyphenylboronic acid, 2.05 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.15 g of N-hydroxysuccinimide to 35 mL of anhydrous dichloromethane solvent, and stir continuously to form a uniform reaction suspension. Then add 2.35 g of 3-aminopropyltriethoxysilane dropwise. After the addition is complete, stir the reaction at 35 °C for 14 h. After the reaction is complete, filter, collect the filtrate and evaporate under reduced pressure to dry, to obtain phenylboronic acid coupling agent.

[0053] (6) Add 135 mL of ethanol and 45 mL of deionized water to the reactor and mix to prepare a solvent. Add 0.18 g of hydroxylated hexagonal boron nitride to the solvent and sonicate for 1.5 h. Then dissolve 0.75 g of phenylboronic acid coupling agent in anhydrous ethanol and add it dropwise to the reactor under stirring. After the addition is complete, stir the reaction at 85 °C for 22 h. After the reaction is complete, cool to room temperature, filter, wash and dry to obtain modified hexagonal boron nitride.

[0054] (7) Add 75 parts by weight of PAO4 base oil, 12 parts by weight of alkyl naphthalene AN30, and 5 parts by weight of viscosity index improver to a mixing vessel, heat to 60°C, stir for 25 min, and then add 0.8 parts by weight of modified phosphate, 0.4 parts by weight of modified hexagonal boron nitride, 4 parts by weight of polyisobutylene succinimide, 1 part by weight of composite antioxidant, and 0.01 parts by weight of defoamer in sequence. Then, ultrasonically stir at 75°C for 1.5 h, filter the mixture through a 200-mesh precision filter, and cool to obtain low-temperature start-up type four-stroke UAV engine lubricating oil.

[0055] Furthermore, the composite antioxidant is composed of 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine in a mass ratio of 1:1.5.

[0056] Comparative Example 1

[0057] The main difference between this comparative example and Example 3 is that bis(trimethylolpropane) phosphate is used instead of modified phosphate, while the remaining components and preparation methods are exactly the same as in Example 3.

[0058] Comparative Example 2

[0059] The main difference between this comparative example and Example 3 is that unmodified hexagonal boron nitride is used instead of modified hexagonal boron nitride, while the remaining components and preparation methods are exactly the same as in Example 3.

[0060] Comparative Example 3

[0061] The main difference between this comparative example and Example 3 is that only 1 part by weight of a single phenolic antioxidant (2,6-di-tert-butyl-p-cresol) was used for the antioxidant component, dioctyl diphenylamine was not added, and there was no compound synergistic antioxidant system. The remaining components and preparation methods are exactly the same as in Example 3.

[0062] Comparative Example 4

[0063] The main difference between this comparative example and Example 3 is that alkyl naphthalene AN30 is not added, and its original 12 parts by weight are replaced with an equal amount of PAO4 base oil (i.e., the amount of PAO4 base oil added becomes 87 parts by weight). The remaining components and preparation methods are exactly the same as in Example 3.

[0064] Performance testing

[0065] The lubricating oils prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests.

[0066] (1) Kinematic viscosity and viscosity index

[0067] Kinematic viscosity: The kinematic viscosity of the oil was determined according to ASTM D445 standard. Test temperatures were 40℃ and 100℃, using a constant temperature bath with a temperature control accuracy of ±0.1℃, and an Ubbelohde capillary viscometer calibrated with national metrological standard oils. Each sample was measured in triplicate, and the arithmetic mean was taken as the final result. The kinematic viscosity result was retained to two decimal places.

[0068] Viscosity index: The viscosity index is calculated according to the kinematic viscosity at 40°C and 100°C, based on the ASTM D2270 standard, and the result is rounded to the nearest integer.

[0069] (2) Low-temperature dynamic viscosity

[0070] The apparent viscosity of engine oil at low temperatures was determined according to GB / T 6538-2022 "Determination of Apparent Viscosity of Engine Oil - Cold Start Simulator Method". Test temperatures were -25℃ and -30℃. A cold start simulator viscometer was used for measurement. Before testing, the instrument was calibrated using standard calibration oil. After the oil sample was kept at the set temperature for 30 minutes to achieve equilibration, data were collected and recorded. The apparent viscosity of the oil at the corresponding temperature was expressed in mPa·s, and the results were rounded to the nearest integer.

[0071] (3) High temperature and high shear viscosity

[0072] The high-temperature, high-shear viscosity of the oil was determined according to the standard SH / T 0703-2001 "Determination of Apparent Viscosity of Lubricating Oils under High Temperature and High Shear Rate Conditions (Multiple Capillary Viscometer Method)". The test temperature was 150℃, and the shear rate was 10. 6 s -1 The measurements were performed using a multiple capillary viscometer. The instrument was calibrated with a standard viscosity solution before testing. Each sample was measured in triplicate, and the arithmetic mean was taken as the final result, expressed in mPa·s, rounded to two decimal places.

[0073] (4) Four-ball machine test

[0074] Maximum non-seize load (PB) and sintering load (PD): determined according to GB / T 12583-1998 "Determination of Extreme Pressure Properties of Lubricants (Four-Ball Method)". Four steel balls with a diameter of 12.7 mm are arranged in an equilateral tetrahedral configuration. The upper ball is rotated at a speed of 1450±50 r / min. The load is increased step by step, with each load increment lasting 10 s. The maximum load at which the steel balls do not seize is recorded as the PB value (N). The load is then increased step by step, and the minimum load at which the steel balls sinter is recorded as the PD value (N).

[0075] (5) Coking plate test

[0076] The tendency of oil to form high-temperature deposits was determined according to SH / T 0300-1992 "Crankcase Simulation Test Method (Coking Plate Method)". The oil sample was splashed onto a heated aluminum plate at a certain flow rate, and the temperature of the aluminum plate was maintained at 320±5℃. The test lasted for 3 hours. After the test, the mass of coke formed on the aluminum plate was weighed, which is the coke weight, and the unit is mg.

[0077] The test results are shown in Table 1.

[0078] Table 1: Performance Tests

[0079] Example 1 9.85 158 2750 4050 3.12 981 2452 12.5 Example 2 10.42 162 2880 4220 3.25 1236 3089 10.2 Example 3 10.15 160 2810 4180 3.18 981 2452 11.4 Comparative Example 1 9.68 145 3210 4680 2.92 784 1961 68.5 Comparative Example 2 9.75 147 3580 5250 2.98 784 1961 28.5 Comparative Example 3 10.10 159 2830 4150 3.15 981 2452 85.6 Comparative Example 4 9.55 165 2950 4730 2.90 618 1961 35.4

[0080] As can be seen from Table 1, the lubricating oils prepared in Examples 1-3 have good low-temperature starting performance, high-temperature high-shear performance and extreme pressure anti-wear performance.

[0081] The comparison shows that Comparative Example 1 uses bis(trimethylolpropane) diphosphate instead of modified phosphate. The acidic bis(trimethylolpropane) diphosphate easily corrodes the friction pair surface and cannot form a dense chemical protective film. At the same time, it lacks the polar physical adsorption effect and steric hindrance effect of long-chain octadecylamine, which not only reduces the extreme pressure anti-wear ability, but also causes the additive to easily pyrolyze and carbonize at high temperatures, generating a large amount of sludge and carbon deposits, thus reducing performance. Comparative Example 2 uses unmodified hexagonal boron nitride instead of modified hexagonal boron nitride. Ordinary hexagonal boron nitride without phenylboronic acid coupling agent is prone to agglomeration in non-polar base oil, inducing the premature precipitation of local ordered structures in the oil, resulting in an increase in low-temperature apparent viscosity. Moreover, lacking the anchoring effect of phenylboronic acid groups, boron nitride cannot effectively spread at the metal interface to form a double-layer lubricating film, resulting in a decrease in load-bearing capacity. Comparative Example 3 used only 1 part by weight of a single phenolic antioxidant (2,6-di-tert-butyl-p-cresol) without adding dioctyl diphenylamine. Lacking a synergistic antioxidant system, the single phenolic antioxidant was rapidly depleted during prolonged high-altitude, high-temperature operation of the drone, leading to deep oil oxidation, severe high-temperature coking, and performance degradation. Comparative Example 4 did not add alkyl naphthalene AN30, replacing its original 12 parts by weight with an equal amount of PAO4 base oil. Pure PAO4 base oil has extremely weak polarity, resulting in poor solubility and inclusion of polar additives and nano-dispersions. The additives could not be uniformly and stably dispersed in the oil phase, significantly reducing the high-temperature oil film strength. Furthermore, PAO4 molecules have high regularity, easily crystallizing at low temperatures, thus losing the crystal-destructive effect of alkyl naphthalene. Cold-start viscosity increased abnormally. Although PAO4 itself has better viscosity-temperature characteristics than alkyl naphthalene, and removing alkyl naphthalene improved the viscosity index, the cost was severely deteriorated low-temperature start-up performance, proving that a high viscosity index alone cannot meet the requirements of drone low-temperature operations.

[0082] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0084] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A low-temperature start-up type four-stroke unmanned aerial vehicle engine lubricating oil, characterized in that, It includes the following components by weight: 70-80 parts by weight of PAO4 base oil, 10-15 parts by weight of alkyl naphthalene AN30, 4-6 parts by weight of viscosity index improver, 0.5-1 parts by weight of modified phosphate, 0.3-0.5 parts by weight of modified hexagonal boron nitride, 3-5 parts by weight of polyisobutylene succinimide, 1-2 parts by weight of composite antioxidant, and 0.01-0.02 parts by weight of defoamer.

2. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 1, characterized in that, The modified phosphate is prepared by: Step 1: Add bis(trimethylolpropane), phosphorus oxychloride and 1,4-dioxane to the reactor, mix well, and react at 50-60℃ for 4-6 hours. After the reaction is completed, vacuum distill and dry to obtain bis(trimethylolpropane) diphosphorus chloride. Step 2: Dissolve bis(trimethylolpropane) diphosphate chloride in 1,4-dioxane, then add deionized water dropwise to the solution. After the addition is complete, react at 70-80℃ for 1-2 hours. After the reaction is complete, distill under reduced pressure and dry to obtain bis(trimethylolpropane) diphosphate. Step 3: Dissolve bis(trimethylolpropane) phosphate in 1,4-dioxane, then add octadecylamine to the solution, stir and mix, and react at 60-65℃ for 3-4 hours. After the reaction is complete, vacuum distill, wash and dry to obtain the modified phosphate.

3. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 2, characterized in that, In step one, the ratio of the amounts of bis(trimethylolpropane), phosphorus oxychloride, and 1,4-dioxane is 2.5-2.6g:3.8-3.9g:5-8mL.

4. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 2, characterized in that, In step two, the ratio of bis(trimethylolpropane) diphosphine chloride, 1,4-dioxane, and deionized water is 4-4.1g:2-3mL:0.5-0.6g.

5. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 2, characterized in that, In step three, the ratio of the amounts of bis(trimethylolpropane) phosphate, 1,4-dioxane, and octadecylamine is 3.3-3.4g:8-10mL:4.5-4.6g.

6. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 1, characterized in that, The method for preparing the modified hexagonal boron nitride is as follows: S1: Isopropanol and deionized water are added to the reactor and mixed to obtain a solution. Hexagonal boron nitride is added to the solution and ultrasonically treated for 1-1.5 hours. Then, the mixed solution is ultrasonically exfoliated using an ultrasonic cleaner for 10-12 hours. After the reaction is completed, the solution is centrifuged at 4500-5000 rpm for 30-40 minutes. The supernatant obtained after centrifugation is vacuum filtered and vacuum dried at 90-100℃ for 12-14 hours to obtain hydroxylated hexagonal boron nitride. S2: Add 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to anhydrous dichloromethane solvent, and stir continuously to form a uniform reaction suspension. Then, add 3-aminopropyltriethoxysilane dropwise. After the addition is complete, stir the reaction at 30-40℃ for 12-16 h. After the reaction is complete, filter, collect the filtrate and evaporate it under reduced pressure to dry it, and obtain the phenylboronic acid coupling agent. S3: Add 120-150 mL of ethanol and 40-50 mL of deionized water to the reactor to prepare a solvent. Add 0.15-0.2 g of hydroxylated hexagonal boron nitride to the solvent and sonicate for 1-2 h. Then, dissolve 0.7-0.8 g of phenylboronic acid coupling agent in anhydrous ethanol and add it dropwise to the reactor with stirring. After the addition is complete, stir the reaction at 80-90℃ for 20-24 h. After the reaction is complete, cool to room temperature, filter, wash and dry to obtain modified hexagonal boron nitride.

7. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 5, characterized in that, The ratio of isopropanol, deionized water, and hexagonal boron nitride in S1 is 120-150 mL: 120-150 mL: 1.3-1.5 g.

8. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 6, characterized in that, The ratio of anhydrous dichloromethane, 4-carboxyphenylboronic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and 3-aminopropyltriethoxysilane in S2 is 30-40 mL: 1.6-1.7 g: 2-2.1 g: 1.1-1.2 g: 2.3-2.4 g.

9. The low-temperature start-up type four-stroke UAV engine lubricating oil according to claim 1, characterized in that, The composite antioxidant is composed of 2,6-di-tert-butyl-p-cresol and dioctyl diphenylamine in a mass ratio of 1:1 to 1:

2.

10. A method for preparing a low-temperature start-up type four-stroke unmanned aerial vehicle engine lubricating oil as described in any one of claims 1-9, characterized in that, The preparation method of the low-temperature start-up type four-stroke UAV engine lubricating oil is as follows: PAO4 base oil, alkyl naphthalene AN30, and viscosity index improver are added to a mixing vessel, heated to 55-65℃, and stirred for 20-30 minutes. Then, modified phosphate, modified hexagonal boron nitride, polyisobutylene succinimide, composite antioxidant, and defoamer are added sequentially. The mixture is then ultrasonically stirred at 70-80℃ for 1-2 hours. The mixture is filtered through a 180-200 mesh precision filter and cooled to obtain the low-temperature start-up type four-stroke UAV engine lubricating oil.