Natural gas engine oil and preparation method thereof

Abstract

The invention relates to the technical field of lubricating oil, in particular to natural gas engine oil and a preparation method thereof. The invention relates to natural gas engine oil which is prepared from the following components in percentage by weight: 70%-80% of hydrogenated base oil, 10.0%-15.0% of a complexing agent and 5.0%-10.0% of an additive, wherein the complexing agent comprises an alkylphenol antioxidant, an alkaryl sulfonate detergent, zinc alkyl dithiophosphate, a borate antioxidant and an arylamine anti-nitration agent; and the additive comprises 1.5%-3.0% of MoDTC (Molybdenum Diethylene Terephthalate).

Description

Technical Field

[0001] This invention relates to the field of lubricating oil technology, and in particular to a natural gas engine oil and its preparation method. Background Technology

[0002] With increasingly stringent environmental regulations and improved utilization of natural gas resources, natural gas engines (including CNG, LNG, and biogas fuel engines) are widely used in public transportation, power generation, and heavy-duty transportation due to their advantages such as clean emissions and low operating costs. However, compared to traditional gasoline or diesel engines, natural gas engines have significant differences in combustion characteristics and operating conditions, placing higher demands on lubricating oil performance.

[0003] On the one hand, natural gas fuel has a higher combustion temperature, resulting in higher levels of nitrogen oxides (NOx) in the combustion exhaust. A significantly increased concentration of certain chemicals makes lubricating oil more susceptible to oxidation and nitration degradation, leading to decreased viscosity, increased acid value, decreased base value, and deposit accumulation, severely impacting oil change intervals and engine reliability. Current technologies often employ a composite system consisting of alkylphenol antioxidants, detergents, and zinc-containing anti-wear additives (ZDDP). However, this approach is insufficient for addressing the high temperatures associated with natural gas engines. Their effectiveness in addressing nitrification failure under environmental conditions is limited. Furthermore, traditional antioxidants are prone to failure at high temperatures or during prolonged operation, have short antioxidant induction periods, and struggle to achieve the goal of "long lifespan."

[0004] On the other hand, natural gas engines generally exhibit low-speed pre-ignition (LSPI) and dry friction tendencies, placing higher demands on the friction improvement and wear suppression capabilities of fuels. While ZDDP-type additives possess certain anti-wear properties, their high-temperature decomposition may affect the exhaust aftertreatment system, and the resulting friction film is unstable. MoDTC-type friction modifiers, due to their ability to release [resources] under high-temperature conditions, offer alternatives. or These compounds have attracted attention due to their ability to form solid lubricating films. However, they are prone to deactivation in harsh oxidizing environments, which affects their durability of friction improvement and limits their widespread application in natural gas engine oil systems.

[0005] Therefore, existing natural gas engine oils generally have the following technical problems:

[0006] (1) Insufficient antioxidant / antinitrification capabilities, making it difficult to support long-term oil change cycles;

[0007] (2) Friction modifiers have poor thermal stability and limited wear inhibition capabilities;

[0008] (3) There is a lack of synergistic and efficient composite agent system, which cannot simultaneously address oxidation, nitration and friction failure mechanisms. Summary of the Invention

[0009] This invention covers the following technical solutions:

[0010] One aspect of the present invention relates to a natural gas engine oil, which, by weight percentage, comprises the following components:

[0011] Hydrogenated base oil 70%–80%, compounding agent 10.0%–15.0%, and additives 5.0%–10.0%;

[0012] The composite agent includes alkylphenol antioxidants, alkylaryl sulfonate detergents, zinc alkyl dithiophosphate, borate antioxidants, and arylamine antinitrification agents.

[0013] The additive contains 1.5% to 3.0% MoDTC.

[0014] Another aspect of the present invention relates to a method for preparing the natural gas engine oil as described above, comprising the following steps:

[0015] Mix all ingredients thoroughly and filter to remove impurities.

[0016] This invention proposes a composite agent system that incorporates borate ester antioxidants and arylamine antinitrification agents to synergistically improve the performance of oil products at high temperatures and... The oil exhibits improved oxidation stability and base number retention under operating conditions, and incorporates a high dose of MoDTC friction modifier. Under the protection of the aforementioned antioxidant system, a denser and more durable friction film is formed, thereby significantly enhancing the overall performance and service life of natural gas engine lubricating oil. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 The illustration shows the embodiments of the present invention and the comparative examples. Comparison of nitrate ester formation under induced conditions. The smaller the value, the better the oil's resistance to nitrification.

[0019] Figure 2The figure shows a comparison of the wear scar diameters in a four-ball friction test between Example 3 of the present invention and two comparative examples, reflecting the anti-wear performance of different lubricant samples. The samples include Comparative Example 1 (Control) without MoDTC, Comparative Example 2 (MoDTC only) containing only MoDTC but without borate esters and arylamines, and Example 3 of the present invention, which contains both MoDTC and a synergistic antioxidant system. The smaller the value, the more stable the lubricating film and the better the anti-wear effect. Detailed Implementation

[0020] Reference will now be made to detailed embodiments of the present invention, one or more of which are described below. Each example is provided for explanation and not for limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0021] Unless otherwise stated, all terms used to disclose this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance is provided below for a better understanding of the teachings of this invention. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0022] The terms "and / or," "or / and," and "and / or" as used herein include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that in this invention, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR." For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0023] The terms “containing,” “comprising,” and “including” as used in this invention are synonyms and are inclusive or open-ended, not excluding additional, uncited members, elements, or method steps.

[0024] In this invention, the numerical range represented by endpoints includes all numerical values ​​and fractions contained within that range, as well as the endpoints mentioned.

[0025] As used in this invention, the term "about" or "approximately" means within 20%, preferably within 10%, and more preferably within 5%, of a given value or range. It also includes specific numbers, such as about 20 including 20.

[0026] Furthermore, in describing representative embodiments of the invention, this specification may present the methods and / or processes of the invention as a specific sequence of steps. However, the method or process should not be limited to the specific order of the steps described herein, to the extent that the method or process does not depend on the specific order of the steps presented herein. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps presented in the specification should not be construed as a limitation of the claims. Additionally, the claims relating to the methods and / or processes of the invention should not be limited to the execution of their steps in the order they are written, and those skilled in the art will readily recognize that the sequence can be changed while still remaining within the spirit and scope of the invention.

[0027] This invention relates to concentration values, which include fluctuations within a certain range. For example, fluctuations are allowed within a corresponding precision range. For instance, 2% can fluctuate within ±0.1%. For larger values ​​or values ​​that do not require overly precise control, even greater fluctuations are permitted. For example, 100mM can fluctuate within ranges of ±1%, ±2%, ±5%, etc.

[0028] As used in this invention, unless otherwise stated, the singular forms of the articles “a,” “an,” and “the” include plural referents.

[0029] In this invention, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity of 2 or more.

[0030] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0031] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" merely describe implementation methods or embodiments with better effects and should be understood not to limit the scope of protection of this invention. In this invention, terms such as "optionally," "optionally," and "optional" mean that something is optional, that is, selected from either "with" or "without" a parallel solution. If multiple "optional" statements appear in a technical solution, unless otherwise specified and without contradiction or mutual constraint, each "optional" statement is independent.

[0032] The first aspect of the present invention relates to a natural gas engine oil, which, by weight percentage, comprises the following components:

[0033] Hydrogenated base oil 70%–80%, compounding agent 10.0%–15.0%, and additives 5.0%–10.0%;

[0034] The composite agent includes alkylphenol antioxidants, alkylaryl sulfonate detergents, zinc alkyl dithiophosphate, borate antioxidants, and arylamine antinitrification agents.

[0035] The additive contains 1.5% to 3.0% MoDTC.

[0036] The aforementioned natural gas engine oil, by combining hydrotreated base oil, compound agents, and additives in specific mass percentages, constructs a highly stable lubrication system with anti-oxidation, anti-nitration, and anti-wear properties. The medium to high dosage (1.5%–3.0%) of MoDTC can efficiently form a low-shear friction film in the antioxidant environment composed of aryl amines and borate esters, thereby improving performance in natural gas engines. In applications with high concentrations and high heat loads, it significantly extends oil change intervals and reduces wear and deposit formation.

[0037] To improve the stability of oil products under different operating conditions, in some embodiments, the additives include viscosity index improvers, pour point depressants, and antifoaming agents. Pour point depressants help maintain sufficient fluidity during cold starts at low temperatures, antifoaming agents suppress foam interference with lubricating film formation under high loads, and viscosity index improvers ensure effective oil film thickness is maintained in high shear zones.

[0038] In some embodiments, the hydrotreated base oil includes Group II and / or Group III hydrotreated base oils.

[0039] In some embodiments, the viscosity index improver content is 3.0% to 8.0%, comprising hydrogenated styrene-diene copolymer and polyolefin shear stabilizer (OCP). Unless otherwise specified in this invention, the amounts of hydrogenated styrene-diene copolymer and polyolefin shear stabilizer added are the same.

[0040] In some embodiments, the pour point depressant content is 0.2% to 0.5%, comprising a combination of acrylate copolymer and microcrystalline wax. Unless otherwise specified in this invention, the amounts of acrylate copolymer and microcrystalline wax added are the same.

[0041] In some embodiments, the antifoaming agent content is 0.01% to 0.05%, including non-silicone fluorinated antifoaming agents.

[0042] In some embodiments, the MoDTC is molybdenum dialkyldithiocarbamate, whose decomposition products form a lubricating surface containing... or The friction film.

[0043] In some embodiments, the compound agent in the natural gas engine oil comprises 2.25% to 5.25% alkylphenol antioxidants, 1.80% to 4.50% alkylaryl sulfonate detergents, 0.90% to 3.00% zinc alkyl dithiophosphate, 0.90% to 3.00% borate ester antioxidants, and 0.45% to 1.50% arylamine antinitrification agents.

[0044] In some embodiments, the aryl amine antinitrifying agent in the natural gas engine oil is a diphenylamine or an alkyl-substituted aryl amine; the borate ester antioxidant is an alkyl-substituted fatty alcohol borate ester or a phenolic borate ester.

[0045] According to another aspect of the present invention, a method for preparing the natural gas engine oil as described above is provided, comprising the following steps:

[0046] Mix all ingredients thoroughly and filter to remove impurities.

[0047] The embodiments of the present invention will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this invention, or follow experimental manuals or conventional conditions in the art, or other experimental methods known in the art, or follow the conditions recommended by the manufacturer.

[0048] In the specific embodiments described below, the measurement parameters involving raw material components may have slight deviations within the weighing accuracy range unless otherwise specified. Temperature and time parameters are subject to acceptable deviations due to instrument testing accuracy or operational precision.

[0049] The components and formulations in the examples are as follows.

[0050] Components Example 1 (Balanced Proportion) Example 2 (High Antioxidant Type) Example 3 (High Wear Resistance Type) Hydrogenated base oil (Group II / III) - GS LBO150N 74 71 72.5 Alkylphenol antioxidants - BHT (Ionol) 3.5 4.2 2.8 Alkyl aryl sulfonate detergent - C14-16 alkylbenzene sulfonate calcium 2.8 3 2 Zinc Alkyl Dithiophosphate - ZDDP (Lubrizol® 1395) 1.5 1.2 2.5 Boronate antioxidants - triisobutyrate 1.5 2.5 1 Aryl amine antinitrifying agent - Alkyl diphenylamine (Naugard® 445) 0.7 1 0.7 Friction modifier - MoDTC (OLOA® 9750) 2 2 3 Viscosity index improver - Infineum SV261 + OCP 6 6 6.5 Pour point depressant - VISCOPLEX 1-254 + microcrystalline wax (Shellwax 120) 0.4 0.5 0.3 Antifoaming agent - Non-silicone fluorinated antifoaming agent (Tego® Antifoam 3062) 0.1 0.1 0.2 total 100 100 100

[0051] Example 1

[0052] Weigh the following raw materials by weight percentage: hydrotreated base oil (GS LBO150N) 74.0%, alkylphenol antioxidant (BHT, trade name Ionol) 3.5%, alkylaryl sulfonate detergent (C14-16 alkylbenzene sulfonate calcium) 2.8%, alkyl dithiophosphate zinc (ZDDP, trade name Lubrizol® 1395) 1.5%, borate antioxidant (triisobutyrate borate) 1.5%, aryl amine antinitrification agent (alkyl diphenylamine, trade name Naugard® 445) 0.7%, friction modifier (MoDTC, trade name OLOA® 9750) 2.0%, viscosity index improver (Infineum SV261 blended with polyolefin OCP) 6.0%, pour point depressant (acrylate VISCOPLEX 1-254 and microcrystalline wax Shellwax) 0.4% of the 120 combination, and 0.1% of the non-silicone fluorinated antifoam agent (Tego® Antifoam 3062).

[0053] The above-mentioned raw materials were added sequentially to a reaction vessel and stirred at 60°C for 30 minutes to ensure that all components were fully dissolved and mixed evenly, resulting in a clear and transparent lubricating oil composition. The obtained product was cooled to room temperature and filtered to remove impurities, thus obtaining the natural gas engine oil described in Example 1.

[0054] The borate ester antioxidant and arylamine antinitrification agent in this formula work synergistically to effectively inhibit the oxidation and nitrification failure of the oil in the high-temperature natural gas combustion environment, thus extending the service life of the oil. At the same time, under the protection of the above-mentioned antioxidant system, MoDTC can stably release the MoS2 lubricating film, effectively reducing the friction and wear in the cylinder liner-piston area, making it suitable for modern natural gas engines with high heat load and low-speed pre-ignition tendency.

[0055] Example 2

[0056] Weigh the following raw materials by weight percentage: hydrotreated base oil (GS LBO150N) 71.0%, alkylphenol antioxidant (BHT, trade name Ionol) 4.2%, alkylaryl sulfonate detergent (C14-16 alkylbenzene sulfonate calcium) 3.0%, alkyl dithiophosphate zinc (ZDDP, Lubrizol® 1395) 1.2%, borate antioxidant (triisobutyrol borate) 2.5%, aryl amine antinitrification agent (alkyl diphenylamine, Naugard® 445) 1.0%, friction modifier (MoDTC, OLOA® 9750) 2.0%, viscosity index improver (Infineum SV261 + OCP) 6.0%, pour point depressant (VISCOPLEX 1-254 + Shellwax 120) 0.5%, and antifoaming agent (Tego® Antifoam 3062) 0.1%.

[0057] The above components were added to a mixing vessel in sequence and stirred at 65°C for 40 minutes. The mixture was observed to be uniform and transparent. After filtration, the natural gas engine oil described in Example 2 was obtained.

[0058] This formulation features a significantly increased content of borate esters and arylamines, constructing a multi-component synergistic antioxidant system based on alkylphenols and ZDDP. This significantly enhances the oxidation induction period and base number retention capacity under high-temperature conditions. It is suitable for gas-powered vehicles or heavy-duty engines with long oil change intervals and stringent emission controls.

[0059] Example 3

[0060] Weigh the following raw materials by weight percentage: hydrotreated base oil (GS LBO150N) 72.5%, alkylphenol antioxidant (BHT, Ionol) 2.8%, alkylaryl sulfonate detergent (C14-16 alkylbenzene sulfonate calcium) 2.0%, alkyl dithiophosphate zinc (ZDDP, Lubrizol® 1395) 2.5%, borate antioxidant (triisobutyrate borate) 1.0%, arylamine antinitrification agent (alkyl diphenylamine, Naugard® 445) 0.7%, friction modifier (MoDTC, OLOA® 9750) 3.0%, viscosity index improver (Infineum SV261 + OCP) 6.5%, pour point depressant (VISCOPLEX 1-254 + Shellwax 120) 0.3%, and antifoaming agent (Tego® Antifoam 3062) 0.2%.

[0061] The components were added to the reaction vessel at 60°C and stirred for 35 minutes. After thorough mixing, the mixture was cooled and filtered to obtain the natural gas engine oil described in Example 3.

[0062] In this formulation, MoDTC and ZDDP synergistically construct a friction film, which remains stable in a borate ester-aromatic amine antioxidant environment, improving the thermal life and lubrication performance of the friction film. This formulation can significantly reduce wear in the engine cylinder liner area and valve system, and is suitable for natural gas-powered vehicles that operate under frequent start-stop and high load conditions.

[0063] Experimental Example

[0064] To verify the technical effectiveness of the composite agent synergistic antinitrification design and high-dose MoDTC friction improvement strategy proposed in this invention, the following comparative experiment was designed and implemented.

[0065] Anti-nitrification performance test:

[0066] Compared to Example 2, the comparative example did not contain arylamines and borate esters, and the missing components were replaced with hydrogenated base oils to fill the gaps.

[0067] use The induced oxidation reaction system was continuously purged with synthesis tail gas (NO₂) at 150°C for 8 hours. The mixture ratio was 1:1 (volume fraction 2000 ppm), and the amount of nitrate esters formed in the oil sample was determined, expressed in mg KOH / g. Results are as follows: Figure 1 As shown, compared with the comparative oil samples without added arylamines and borate esters, Examples 1-3 all exhibited lower nitrate ester formation, with Example 2 showing the lowest level at only 1.7 mg KOH / g, a reduction of over 59% compared to the comparative sample (4.2 mg KOH / g). This indicates that the synergistic antinitrification system of "arylamine + borate ester" used in this invention can significantly inhibit high-temperature nitrification. Induced oil degradation enhances resistance to failure.

[0068] Wear resistance test:

[0069] Comparative Example 1 was the control formulation of Example 3 with MoDTC removed; Comparative Example 2 was the version of Example 3 with MoDTC retained but with borate esters and arylamine additives removed, and the missing components were made up with base oil. All samples were tested by the ASTM D4172 four-ball method, running at 1200 rpm, 392 N load and 75°C for 60 minutes, and the wear scar diameter was measured.

[0070] like Figure 2 As shown, the wear scar diameter in Comparative Example 1, which did not contain MoDTC, was 0.78 mm. In Comparative Example 2, where MoDTC was added alone but without antioxidant protection, the wear scar diameter increased to 0.82 mm. However, the combination of MoDTC and an antioxidant system in Example 3 performed best, with a wear scar diameter of only 0.48 mm. These results indicate that in the absence of arylamine and borate ester protection, the lubricating film of MoDTC is difficult to form sustainably and is easily affected by high-temperature oxidation and decomposition, which may even trigger side reactions leading to increased wear.

[0071] discuss:

[0072] exist Figure 1 shown In the induced nitrate formation test, the natural gas engine oil samples of Examples 1 to 3 all showed significantly better anti-nitrification performance than the comparative examples, especially Example 2 (high antioxidant type), which showed the most outstanding effect. The increase in nitrate esters per unit mass of oil was only 1.7 mg KOH / g, a reduction of more than 59% compared to the 4.2 mg KOH / g of the comparative example. This technical effect is attributed to the synergistic introduction of aryl amine anti-nitrification agents and borate ester antioxidants into the compound agent in this invention.

[0073] Aryl amines (such as alkyl diphenylamines) are known to be highly efficient nitroxide radical scavengers, capable of capturing NO• and... Free radical intermediates, thereby blocking The induced chain nitration process. On the other hand, borate ester antioxidants react chemically with peroxy radicals (ROO•) or hydrogen peroxide intermediates (ROOH) to generate thermally stable borate ester intermediates, effectively terminating the propagation pathway of oxidation chain reactions in oils. The synergistic effect of these two types of components achieves dual-channel blocking of the "oxygen radical pathway" and the "nitrogen-oxygen induced pathway," enabling lubricating oils to withstand high temperatures. It maintains a longer stable service life in the environment, inhibits the accumulation of acidic byproducts and maintains the base value, ultimately significantly improving the anti-nitrification performance and overall stability of natural gas engine oil.

[0074] exist Figure 2 The four-ball anti-wear performance test shown verified the enhanced lubrication and friction reduction effect of MoDTC in this system. MoDTC (molybdenum dialkyl dithiocarbamate), as a thermally decomposable friction modifier, releases... or A boundary lubricating film with low shear strength can be formed at the metal-metal friction interface. However, at high temperatures and high humidity... In the high concentration of natural gas in engine environments, MoDTC is highly susceptible to oxidation and nitridation by free radicals, which can lead to instability or even partial disappearance of the friction film, resulting in lubrication failure.

[0075] The key technology of this invention lies in: synergistically introducing aryl amines and borate esters into the composite agent system to respectively eliminate... Free radical intermediates form a synergistic antioxidant environment, thereby significantly extending the membrane formation cycle and membrane structure integrity of MoDTC. Figure 2 The results of Comparative Example 2 further confirm that without synergistic antioxidant protection, MoDTC's anti-wear ability is actually lower than that of traditional formulations without MoDTC, indicating that the technical effect of MoDTC depends on the presence of a synergistic environment, rather than acting independently. This nonlinear, non-additive lubrication enhancement mechanism constitutes the unexpected technical effect and substantial inventive basis of this invention.

[0076] In summary, Figure 1 and Figure 2 The experimental results show that the "arylamine + borate ester synergistic antioxidant system" proposed in this invention not only improves the antioxidant and anti-nitrification properties of the oil, but also provides a thermally stable protective environment for the high-load added MoDTC friction modifier, enhances the formation efficiency and durability of the lubricating film, and constitutes a synergistic formulation structure in the field of natural gas engine oil.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A natural gas engine oil, comprising, by weight percentage, the following components: Hydrogenated base oil 70%–80%, compounding agent 10.0%–15.0%, and additives 5.0%–10.0%; The composite agent includes alkylphenol antioxidants, alkylaryl sulfonate detergents, zinc alkyl dithiophosphate, borate antioxidants, and arylamine antinitrification agents. The additive contains 1.5% to 3.0% MoDTC.

2. The natural gas engine oil according to claim 1, wherein the additives include a viscosity index improver, a pour point depressant, and an antifoaming agent.

3. The natural gas engine oil according to claim 1, wherein the hydrotreated base oil comprises Group II and / or Group III hydrotreated base oils.

4. The natural gas engine oil according to claim 1, wherein the viscosity index improver content is 3.0% to 8.0%, comprising hydrogenated styrene-diene copolymer and polyolefin shear stabilizer.

5. The natural gas engine oil according to claim 1, wherein the pour point depressant content is 0.2% to 0.5%, comprising a combination of acrylate copolymer and microcrystalline wax.

6. The natural gas engine oil according to claim 1, wherein the antifoaming agent content is 0.01% to 0.05%, including non-silicone fluorinated antifoaming agents.

7. The natural gas engine oil according to claim 1, wherein the compound agent comprises 2.25% to 5.25% alkylphenol antioxidant, 1.80% to 4.50% alkylaryl sulfonate detergent, 0.90% to 3.00% zinc alkyl dithiophosphate, 0.90% to 3.00% borate ester antioxidant, and 0.45% to 1.50% arylamine antinitrification agent.

8. The natural gas engine oil according to claim 1, wherein the aryl amine antinitrifying agent is a diphenylamine or an alkyl-substituted aryl amine; and the borate ester antioxidant is an alkyl-substituted fatty alcohol borate ester or a phenolic borate ester.

9. A method for preparing the natural gas engine oil according to any one of claims 1 to 8, comprising the following steps: Mix all ingredients thoroughly and filter to remove impurities.

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