Composite lubricating oil for improving surface friction performance of cylinder sleeve of diesel engine as well as preparation method and application of composite lubricating oil

Abstract

The invention discloses composite lubricating oil for improving the surface friction performance of a diesel engine cylinder liner and a preparation method and application thereof.The composite lubricating oil is prepared from I-type base oil, MoDTC, ZDDP and TiO2 as components, a Box-Behnken design method is adopted, a screening scheme is generated through Design-Expert software, the mass concentration ratio of the three additives is optimized, the optimal ratio is obtained, and the composite lubricating oil can be used for improving the friction performance of the surface of the diesel engine cylinder liner. The obtained lubricating oil has the minimum average friction coefficient and abrasion mass, can effectively improve the friction performance of a cylinder sleeve and a piston ring, and also makes a major breakthrough in the field of friction reduction of lubricating oil additives. The preparation process is low in cost and does not have too many complicated procedures. Good application prospects are realized.

Description

Technical Field

[0001] This invention relates to the field of friction reduction in lubricating oil additives, specifically to a composite lubricating oil that improves the surface friction performance of diesel engine cylinder liners, its preparation method, and its application. Background Technology

[0002] During the operation of a diesel engine, the cylinder liner and piston rings are the most important friction pair, playing irreplaceable roles in sealing and lubrication. However, the friction loss generated by this pair accounts for approximately 26% of the total friction loss of a diesel engine, and its performance affects the engine's lifespan and stability.

[0003] The friction-reducing and anti-wear properties of lubricating oils are the most critical technical indicators for evaluating lubricating oil products. Currently, widely used lubricating oils consist of both base oil and additives. The use of different additives can effectively reduce wear at the friction interface, thereby enhancing anti-wear performance. The use of lubricating oil additives as a friction-reducing method has already been applied in many fields, including engine parts, marine reduction gears, and nanocomposite materials.

[0004] In existing inventions concerning lubricant additives to improve the friction and wear performance of cylinder liners and piston rings, most research focuses on the application of single additives or a combination of two additives. CN202410606349.3 discloses a potassium borate / graphene nanocomposite lubricant additive, its preparation method, and a composite lubricant. Expanded graphite, potassium borate, and oleic acid are uniformly mixed in a ratio of (14-18) g: (3-5) g: (400-600) ml, and then plasma ball milled to obtain a mixture. After extraction and drying, the potassium borate / graphene nanocomposite lubricant additive is obtained. Adding this to lubricating oil can significantly reduce the corrosion and wear of cylinder liners and piston rings in marine engines operating under low-sulfur fuel conditions. Little attention has been paid to the influence of the combination of two lubricant additives and nanoparticles on the lubrication performance of diesel engine cylinder liners and piston rings under boundary lubrication conditions. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners, its preparation method, and its application, thereby solving the technical problem that existing research on the friction performance of composite lubricating oils on cylinder liners and piston rings and their friction reduction and anti-wear mechanisms is incomplete.

[0006] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:

[0007] A composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners includes a Group I base oil, MoDTC, ZDDP and TiO2 nanoparticles, wherein the mass fraction of TiO2 nanoparticles is 0.65 wt%, the mass fraction of MoDTC is 1.30 wt%, and the mass fraction of ZDDP is 1.03 wt%.

[0008] It should be noted that Group I base oils are used as lubricating media. These hydrocarbon media exhibit typical characteristics of high-quality mineral oils, specifically excellent viscosity-temperature response, significantly suppressed evaporation loss, and superior low-temperature rheological properties. MoDTC contains 9.5%–10.5% molybdenum and 9%–12% sulfur. As a lubricating oil additive, it exhibits excellent friction-reducing, anti-wear, anti-oxidation, and extrusion properties. During friction and wear, MoDTC decomposes to form a reactive film with friction-reducing effects, thus achieving a good friction-reducing effect. ZDDP contains 8.6% zinc, 17.2% sulfur, and 8.1% phosphorus. Due to its anti-oxidation, anti-galling, and anti-wear properties, it is an essential multi-functional additive in lubricants, effectively reducing wear on engine components and improving durability. Under low load conditions, TiO2 nanoparticles form a protective layer on the contact surface through physical adsorption. When subjected to high mechanical stress, they undergo a tribochemical reaction with the metal substrate, generating an in-situ oxide protective film with excellent stability, thereby effectively improving the wear resistance of the material.

[0009] Furthermore, the Group I base oil is 150SN.

[0010] The preparation process of the aforementioned composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners includes the following steps:

[0011] Step 1: Weigh out Group I base oil, MoDTC, ZDDP and TiO2 nanoparticles;

[0012] Step 2: Add MoDTC, ZDDP and TiO2 nanoparticles to the base oil and disperse them using a mechanical stirrer;

[0013] Step 3: Magnetic ultrasonic stirring to ensure good particle dispersion;

[0014] Step 4: Let it stand in the air for later use, thus completing the preparation process of the lubricating oil additive.

[0015] Furthermore, the temperature of the magnetic ultrasonic stirring in step 3 is 60°C.

[0016] Furthermore, the stirring speed in step 3 is 150 rpm.

[0017] Furthermore, the stirring time in step 3 is 2 hours.

[0018] Furthermore, the settling time in step 4 is 0.5 hours.

[0019] The above-mentioned composite lubricant for improving the surface friction performance of diesel engine cylinder liners is applied in the lubrication system of heavy-duty diesel engines.

[0020] Furthermore, the average coefficient of friction of the composite lubricating oil is 0.0621617.

[0021] Furthermore, the wear mass of the composite lubricating oil is 6.82453 mg.

[0022] Beneficial effects:

[0023] Compared with existing technologies, the lubricating oil of this invention uses Group I base oil, MoDTC, ZDDP, and TiO2 as components. Employing the Box-Behnken design method and using Design-Expert software to generate a screening scheme, the mass concentration ratio of the three additives was optimized to obtain the optimal ratio. The resulting lubricating oil exhibits the lowest average coefficient of friction and wear mass, effectively improving the friction performance of the cylinder liner-piston ring, and representing a significant breakthrough in the field of friction reduction through lubricating oil additives. The preparation process of this invention is low-cost and involves few complex steps. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of the lubricating oil additive of the present invention.

[0025] Figure 2 The curves showing the changes in average friction coefficient and wear mass with mass concentration for the addition of a single TiO2 additive in this invention are shown. (a) Average friction coefficient, (b) Wear mass.

[0026] Figure 3 The curves showing the changes in average friction coefficient and wear mass with mass concentration for the addition of a single MoDTC additive in this invention are shown. (a) Average friction coefficient, (b) Wear mass.

[0027] Figure 4 The curves showing the variation of average friction coefficient and wear mass with mass concentration for the addition of a single ZDDP additive in this invention are shown. (a) Average friction coefficient, (b) Wear mass.

[0028] Figure 5 The effect of the interaction between TiO2 and MoDTC mass concentrations on the average friction coefficient and wear quality is shown in (a) average friction coefficient and (b) wear quality.

[0029] Figure 6The interaction between ZDDP and TiO2 mass concentrations is shown to influence the average friction coefficient and wear quality. (a) Average friction coefficient, (b) Wear quality.

[0030] Figure 7 The interaction between ZDDP and MoDTC mass concentrations is shown to influence the average friction coefficient and wear quality. (a) Average friction coefficient, (b) Wear quality.

[0031] Figure 8 This is the result after optimization using the response surface methodology in this invention;

[0032] Figure 9 The curves showing the average friction coefficient and wear quality variation for different additive ratios in this invention are shown.

[0033] Figure 10 The following are the mechanism models for the additives to improve the sample surface in this invention: (a) Mechanism analysis model for additives to improve surface friction performance, (b) Friction reduction analysis model for tribochemical reaction on worn surface, and (c) Wear resistance analysis model for tribochemical reaction on worn surface.

[0034] Figure 11 This is a TEM analysis result of the sample with the optimal additive ratio in this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0036] Example 1

[0037] A method for screening the proportions of TiO2, MoDTC, and ZDDP lubricating oil additives based on BBD response surface analysis is proposed. First, a quadratic regression model is established between the mass concentration ratios of different additives and the average friction coefficient and wear mass. Then, by analyzing the influence of single-factor and interactive factors of additives on tribological properties, the optimal parameters of the mass concentrations of the three additives in the composite lubricating oil are determined. The proportions of the composite lubricating oil additives are optimized using response surface analysis, thereby minimizing the average friction coefficient and wear mass.

[0038] The above method includes the following steps:

[0039] Step 1: Determine the mass concentration ratio range of different additives according to Table 1;

[0040] Table 1. Range of mass concentration ratios for different additives

[0041] <![CDATA[TiO2 mass concentration T (wt%)]]> MoDTC mass concentration M (wt%) ZDDP mass concentration Z (wt%) 0~1 0~2 0~2

[0042] Step 2: Based on the principle of response surface design, three concentration levels (high, medium, and low) were selected for the experiment. Then, the Box-Behnken design method was used to set up three-factor, three-level experimental groups according to Table 2. The average friction coefficient and wear mass were determined as the target response parameters for the boundary lubrication condition. Seventeen experimental schemes were generated using Design-Expert software and prepared and tested according to the following methods. The experimental results were recorded in Table 3 for future reference.

[0043] Table 2. Influencing factors and their levels based on the Box-Behnken experimental design method.

[0044] level <![CDATA[TiO2 mass concentration T (wt%)]]> MoDTC mass concentration M (wt%) ZDDP mass concentration Z (wt%) -1 0 0 0 0 0.5 1 1 1 1 2 2

[0045] Specifically, the preparation method is as follows:

[0046] Step 1: Weigh out Group I base oil, MoDTC, ZDDP and TiO2 nanoparticles;

[0047] Step 2: Add the additive to the base oil and disperse it using a mechanical mixer;

[0048] Step 3: Stir magnetically and ultrasonically at 60℃ for 2 hours to ensure good particle dispersion;

[0049] Step 4: Let it stand in the air for 0.5 hours for later use, thus completing the preparation process of the lubricating oil additive.

[0050] The friction and wear test was conducted using a friction testing machine, and the test method is as follows:

[0051] Step 1, Sample preparation:

[0052] Grind the ball mill cast iron block sample with 800~2000 grit sandpaper until the roughness Ra≤3.2µm. Grind the piston ring pin sample with 2000 grit sandpaper until the roughness Ra≤0.82µm. Clean it ultrasonically with 99% anhydrous ethanol and let it air dry for later use.

[0053] Step 2, clamp the workpiece:

[0054] The block specimen (size: 20mm×20mm×10mm) and the pin specimen (size: diameter 6mm, length 15mm) were fixed on the lower specimen fixture and the upper specimen fixture of the FTM M30 friction testing machine, respectively. The controllable lubrication tribological behavior was characterized using the FTM M30 modular tribological testing system, with the contact pair configured as a pin-slider reciprocating motion mode.

[0055] In the testing system, the upper sample achieves precise control of the normal load through a precision servo loading unit. The maximum range of the normal load of the test device is 500N, and the upper limit of the friction force measurement is also 500N. Its measurement accuracy is 0.1% of the full scale. The lower sample is driven by a linear actuator to achieve reciprocating motion with adjustable displacement amplitude.

[0056] Step 3, determine the operating conditions of the cylinder liner-piston ring:

[0057] The actual cylinder liner-piston ring boundary lubrication test conditions were as follows: 0.1 mm from the top dead center of the cylinder liner, sliding speed of 0.5 m / s, load of 6.1 MPa, and temperature of 303℃. The actual conditions were equivalent to the operating conditions of the friction testing machine: reciprocating frequency: 15 Hz, reciprocating stroke: 6 mm, sampling rate: 100 Hz, normal force: 172 N, temperature: 303℃, and friction time: 60 min.

[0058] Table 3 Response data of average friction coefficient and wear mass in response surface methodology experiments

[0059] serial number <![CDATA[TiO2 mass concentration T (wt%)]]> MoDTC mass concentration M (wt%) ZDDP mass concentration Z (wt%) Average coefficient of friction Wear mass (mg) 1 0 0 1 0.141 18.1 2 1 0 1 0.102 11.7 3 0 2 1 0.106 11.9 4 1 2 1 0.089 9.1 5 0 1 0 0.127 15.3 6 1 1 0 0.103 10.4 7 0 1 2 0.120 14.3 8 1 1 2 0.091 10.1 9 0.5 0 0 0.124 15.1 10 0.5 2 0 0.094 9.7 11 0.5 0 2 0.113 13.5 12 0.5 2 2 0.096 10.9 13 0.5 1 1 0.064 7.5 14 0.5 1 1 0.065 7.6 15 0.5 1 1 0.068 7.7 16 0.5 1 1 0.067 7.8 17 0.5 1 1 0.063 7.4

[0060] Step 3: Import the experimental results into the analysis module of the Design-Expert software to begin the analysis of the response surface.

[0061] Step 4: Using the ANOVA variance analysis module in Design-Expert software, construct a quadratic mathematical model of different additive mass concentration ratios and average friction coefficient (COF) and wear quality (WQ), as shown in Equation (1) and Equation (2);

[0062] (1)

[0063] (2)

[0064] Step 5: Using the model diagram module of Design-Expert software, perform "One Factor" analysis and 3D Surface interaction factor analysis;

[0065] Step 6: Based on the Numerical analysis and solution in the Optimization module, the optimal values ​​of the mass concentrations of the three additives and the feasibility of the prediction results of the mathematical model can be obtained.

[0066] Example 2

[0067] A composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners includes a Group I base oil (150SN), MoDTC, ZDDP, and TiO2 nanoparticles. When the mass concentration of MoDTC is set to 1 wt%, the mass concentration of ZDDP is set to 1 wt%, and the mass concentrations of TiO2 nanoparticles are set to 0.0 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%, respectively. The set parameters are input into step 4 of Example 1 to obtain the following result: Figure 2 The result.

[0068] As shown in the figure, when the mass concentration of TiO2 is 0.0wt%, 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, and 1.0wt%, the average friction coefficients are 0.103, 0.082, 0.069, 0.064, 0.066, and 0.076, respectively, and the wear mass is 12.55mg, 9.93mg, 8.16mg, 7.25mg, 7.19mg, and 7.98mg, respectively.

[0069] In particular, when the mass concentration of MoDTC is 1 wt%, the mass concentration of ZDDP is 1 wt%, and the mass concentration of TiO2 is 0.6 wt%, the average friction coefficient is the minimum of 0.064, and when the mass concentration of TiO2 is 0.7 wt%, the wear mass is the minimum of 7.15 mg.

[0070] Example 3

[0071] A composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners includes a Group I base oil (150SN), MoDTC, ZDDP, and TiO2 nanoparticles. The mass concentrations of TiO2 nanoparticles are set to 0.5 wt%, ZDDP to 1 wt%, and MoDTC to 0.0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%, respectively. These parameters are input into step 4 of Example 1 to obtain the following result. Figure 3 The result.

[0072] As shown in the figure, when the TiO2 mass concentration is 0.5wt%, the ZDDP mass concentration is 1wt%, and the MoDTC mass concentration is 0.0wt%, 0.5wt%, 1.0wt%, 1.5wt%, and 2.0wt%, respectively, the average friction coefficients are 0.098, 0.076, 0.064, 0.065, and 0.074, and the wear mass is 12.14mg, 9.26mg, 7.6mg, 7.16mg, and 7.94mg.

[0073] In particular, the average friction coefficient was the lowest at a MoDTC mass concentration of 1.25 wt%, and the wear mass was the lowest at a MoDTC mass concentration of 1.45 wt%, which was 7.15 mg.

[0074] Example 4

[0075] A composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners includes a Group I base oil (150SN), MoDTC, ZDDP, and TiO2 nanoparticles. The mass concentrations of TiO2 nanoparticles (0.5 wt%), MoDTC (1 wt%), and ZDDP are set to 0.0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%, respectively. These parameters are input into step 4 of Example 1 to obtain the following result. Figure 4 The result.

[0076] As shown in the figure, when the mass concentration of TiO2 is 0.5wt%, the mass concentration of MoDTC is 1wt%, and the mass concentrations of ZDDP are 0.0wt%, 0.5wt%, 1.0wt%, 1.5wt%, and 2.0wt%, respectively, the average friction coefficients are 0.090, 0.072, 0.065, 0.069, and 0.083, and the wear mass is 10.08mg, 8.36mg, 7.6mg, 8.06mg, and 9.65mg.

[0077] In particular, when the ZDDP mass concentration is 1 wt%, the average friction coefficient is the minimum of 0.065 and the wear mass is the minimum of 7.6 mg.

[0078] Example 5

[0079] Based on the optimal additive mass concentration of the interaction factors, the average friction coefficient and wear mass of each group are obtained, and the observed values ​​of the average friction coefficient and wear mass under each experimental condition are obtained, forming a corresponding dataset of "three factors - three levels - target parameters (average friction coefficient and wear mass)". The mathematical expressions of the three lubricating oil additive concentrations with average friction coefficient and wear mass are established by using the quadratic response surface regression method, as shown in equation (1) and equation (2): The effective value ranges of each variable in the expression are as follows: 0 wt%≤T≤1 wt%, 0 wt%≤M≤2 wt%, 0 wt%≤Z≤2 wt%, where COF is the average friction coefficient, WQ is the wear mass, T is the TiO2 mass concentration, M is the MoDTC mass concentration, and Z is the ZDDP mass concentration.

[0080] The Box-Behnken experimental design method was used to validate the predictive model for friction coefficient and wear quality. The results showed that the established quadratic response model was highly statistically significant (P < 0.0001), confirming a significant quantitative relationship between the friction coefficient and each additive component (T, M, Z). Model validation results showed that the lack-of-fit test did not reach a significant level (P > 0.05), indicating that the mathematical model has good predictive accuracy. Specifically, all influencing factors, including linear terms (T, M, Z), interaction terms (TM, MZ), and quadratic terms (T², M², Z²), showed significant effects (P < 0.05). These analytical results fully demonstrate the reliability and accuracy of the established regression model in predicting the relationship between additive ratio and friction coefficient and wear quality.

[0081] Figure 5 To investigate the influence of the interaction between TiO2 and MoDTC mass concentrations on the average friction coefficient and wear quality, when the ZDDP mass concentration is 1 wt%, MoDTC mass concentration is used as the X-axis, TiO2 mass concentration as the Y-axis, and friction coefficient and wear quality as the Z-axis. An interpolation algorithm is used to connect all virtual points into a smooth surface. As the mass concentrations of MoDTC and TiO2 gradually increase, the average friction coefficient decreases from 0.12 to 0.08, exhibiting a nonlinear change characteristic of first decreasing sharply and then increasing slowly. The wear quality exhibits a nonlinear change characteristic of first decreasing significantly and then increasing slowly.

[0082] Figure 6 To investigate the influence of the interaction between ZDDP and TiO2 mass concentrations on the average friction coefficient and wear quality, when the MoDTC mass concentration is 1 wt%, ZDDP mass concentration is used as the X-axis, TiO2 mass concentration as the Y-axis, and friction coefficient and wear quality as the Z-axis. An interpolation algorithm is used to connect all virtual points into a smooth surface. As the mass concentrations of ZDDP and TiO2 gradually increase, the average friction coefficient decreases from 0.12 to 0.07, initially decreasing sharply and then slowly recovering. The wear quality exhibits a nonlinear change characteristic of first decreasing sharply and then gradually increasing.

[0083] Figure 7To investigate the influence of the interaction between ZDDP and MoDTC mass concentrations on the average friction coefficient and wear quality, when the TiO2 mass concentration is 0.5wt%, ZDDP mass concentration is used as the X-axis, MoDTC mass concentration as the Y-axis, and friction coefficient and wear quality as the Z-axis. An interpolation algorithm is used to connect all virtual points into a smooth surface. As the mass concentrations of ZDDP and MoDTC gradually increase, the average friction coefficient decreases from 0.11 to 0.07, exhibiting a nonlinear change characteristic of first significantly decreasing and then gradually increasing. The wear quality also exhibits a nonlinear change characteristic of first significantly decreasing and then gradually increasing.

[0084] like Figure 8 As shown, based on numerical analysis and solution in the Optimization module, when the TiO2 mass concentration T = 0.653291 wt%, the MoDTC mass concentration M = 1.30292 wt%, and the ZDDP mass concentration Z = 1.03421 wt%, the average friction coefficient and wear mass between the cylinder liner and piston ring are minimized under boundary lubrication test conditions, which are 0.0621617 and 6.82453 mg, respectively. The reliability of the predicted results is 97.3%. After retaining two decimal places, the optimal ratio of different additives in the lubricating oil is 0.65 wt% TiO2, 1.30 wt% MoDTC, and 1.03 wt% ZDDP.

[0085] Example 6

[0086] Using TiO2 (0.65 wt%), MoDTC (1.30 wt%), and ZDDP (1.03 wt%) as the optimal proportions, experiments were conducted to determine the optimal ratios for different additives, following the preparation and testing methods described in Example 2. The friction-reducing and wear-resistant mechanism of the additives was analyzed using TEM and established, wherein:

[0087] The SN sample is: the lower sample is a cylinder liner with a smooth surface and base oil (150SN) added;

[0088] The SN-Z sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + ZDDP;

[0089] The SN-M sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + MoDTC;

[0090] The SN-T sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + TiO2;

[0091] The SN-ZM sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + ZDDP + MoDTC;

[0092] The SN-ZT sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + ZDDP + TiO2;

[0093] The SN-MT sample is: the lower sample is a cylinder liner with a smooth surface and added base oil (150SN) + MoDTC + TiO2;

[0094] The SN-ZMT sample is: the sample below is a cylinder liner with a smooth surface and added base oil (150SN) + ZDDP + MoDTC + TiO2.

[0095] The results are as follows Figure 9 As shown in (a)-(b), the average friction coefficient of lubricating oil with one additive shows a rapid decreasing trend. The average friction coefficient of the compound additive is lower than that of the lubricating oil with one additive, and the average friction coefficient shows a gradual decreasing trend. The change trend of wear quality is consistent with the average friction coefficient.

[0096] like Figure 10 (a) shows the analytical model of the mechanism by which additives improve surface friction properties. Figure 10 (b) shows the friction reduction analysis model of the tribochemical reaction on the worn surface. Figure 10 (c) shows the tribochemical reaction anti-wear analysis model of the worn surface. Combined analysis of the three models reveals that in the single additive system (SN-Z, SN-M, SN-T), ZDDP decomposes zinc sulfide (ZnS) and zinc phosphate (Zn3(PO4)2). ZnS, through its unique layered crystal structure, plays a friction-reducing role during friction. The weak bonding force between its sulfur atom layers allows slippage under shear, thereby reducing the friction coefficient and significantly reducing adhesive wear and abrasive wear. In MoDTC, the Mo-S and SC bonds break, generating MoS2, MoO3, and S. -2 Among them, MoS2 achieves excellent friction reduction through its unique layered crystal structure. In its hexagonal crystal system, adjacent sulfur atoms are bonded by weak van der Waals forces, making them easily slippery under shear, significantly reducing adhesive and abrasive wear. MoO3 effectively reduces wear through tribochemical reactions and surface film formation mechanisms, significantly reducing oxidative and thermal wear. TiO2 nanoparticles form a dense boundary lubricating film on the contact surface, reducing roughness and direct contact by filling surface micro-protrusions, thus effectively reducing abrasive wear. The composite additive system exhibits even more significant advantages. The reaction with the iron oxide layer produces iron phosphate (FePO4). FePO4 then reacts with the metal surface to form a dense boundary lubricating film composed of an iron phosphate complex and iron oxide. This film exhibits high hardness and chemical stability, effectively isolating the direct contact of the friction pair and bearing the load, thereby reducing oxidative wear and abrasive wear. Meanwhile, TiO2 reacts with metal ions (Zn...) 2+ Alternatively, phosphate reaction can generate ZnTiO3, which will undergo tribochemical reaction with the metal surface to form a composite protective film composed of zinc titanate, zinc oxide and titanium oxide to reduce wear quality, thereby reducing abrasive wear and thermal wear.

[0097] To further investigate the influence mechanism of ZDDP-MoDTC-TiO2 lubricant additives on the friction film and their macroscopic regulation of friction, focused ion beam (FIB) technology was used to obtain cross-sectional lamellar samples in the ZDDP-MoDTC-TiO2 lubrication region under a load of 6.1 MPa, and the samples were analyzed by high-resolution transmission electron microscopy (HRTEM). The results are as follows: Figure 11 As shown, Figure (a) is a magnified view of the worn surface at 1×10. 4 The cross-section seen under magnification, (b) is a magnified view of the worn surface at 2×10. 4 The cross-section seen under magnification, (c) is a magnified view of the worn surface at 1×10. 5 The cross-section observed under magnification shows that the friction film can be roughly divided into three layers: a platinum protective upper layer, a middle friction film layer, and an iron substrate lower layer. The middle friction film layer includes the upper and lower friction film layers. Figures (d1)-(d10) show the energy dispersive spectroscopy (TEM-EDS) analysis of the friction film cross-section. It can be seen that the friction film is mainly composed of elements such as iron (Fe), carbon (C), manganese (Mn), molybdenum (Mo), oxygen (O), phosphorus (P), sulfur (S), titanium (Ti), and silicon (Si). Figures (e) and (f) show that the uppermost layer of the friction film, beneath the platinum (Pt) protective layer, is enriched with many TiO2 crystals. Energy dispersive spectroscopy analysis of the middle layer reveals that phosphorus (P) is enriched on the surface of the friction film and reacts with oxygen and... The overlap of other metal elements further confirms the function of phosphate as a friction-reducing layer. Figure (g) magnifies the TiO2 crystals and sulfide salt layer, revealing that MoS2 is widely distributed in the friction film in an amorphous lamellar form, further confirming the formation of molybdenum disulfide during the friction reaction. Figure (h) shows that some Ti elements are concentrated in the uppermost layer of the friction film, still existing as TiO2 crystals. In Figure (f), some TiO2 crystals coexist with MoS2 in the sulfide salt layer. In Figure (g), another part of the Ti elements without TiO2 crystals were not observed. Combined with the surface EDS results, this further verifies that the distribution properties are amorphous titanates. As shown in Figures (i)-(k), at the interface between the outer lower layer and the Fe substrate layer, sulfur (S) elements combine with iron (Fe) elements to form ferrous sulfide (FeS) crystals, which exist at the bottom of the friction film.

[0098] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, all of which fall within the scope defined by the appended claims.

Claims

1. A composite lubricating oil for improving the surface friction performance of diesel engine cylinder liners, characterized in that, The I-class base oil, MoDTC, ZDDP and TiO2 nanoparticles are included, the mass fraction of the TiO2 nanoparticles is 0.65 wt%, the mass fraction of the MoDTC is 1.30 wt%, and the mass fraction of the ZDDP is 1.03 wt%.

2. The compound lubricating oil for improving the frictional properties of the surface of a cylinder liner of a diesel engine according to claim 1, characterized by comprising: The I-class base oil is 150SN.

3. A process for the preparation of a composite lubricating oil for improving the frictional properties of the surface of the cylinder liner of a diesel engine according to claim 1, characterized in that, The method comprises the following steps: Step 1, weighing the I-class base oil, MoDTC, ZDDP and TiO2 nanoparticles; Step 2, adding the MoDTC, ZDDP and TiO2 nanoparticles into the base oil and stirring and dispersing by a mechanical stirrer; Step 3, magnetic ultrasonic stirring to ensure good dispersion of the particles; Step 4, standing in the air for standby, completing the preparation process of the lubricating oil additive.

4. The production method according to claim 3, characterized by, The temperature of the magnetic ultrasonic stirring in Step 3 is 60℃.

5. The preparation method according to claim 3, characterized in that, The stirring speed in Step 3 is 150 rpm.

6. The preparation method according to claim 3, characterized in that, The stirring time in Step 3 is 2 h.

7. The preparation method according to claim 3, characterized in that, The standing time in Step 4 is 0.5 h.

8. Application of the composite lubricating oil for improving the friction performance of the surface of a diesel engine cylinder liner to a lubricating system of a heavy-duty diesel engine according to claim 1.

9. Use according to claim 8, characterized in that, The average friction coefficient of the composite lubricating oil is 0.0621617.

10. Use according to claim 8, characterized in that, The wear mass of the composite lubricating oil is 6.82453 mg.

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