US20180291305A1

US20180291305A1 - Nano Suspension Lubricants

Info

Publication number: US20180291305A1
Application number: US15/766,509
Authority: US
Inventors: Annaji Rajiv Kumar Tompala; Srinivas Vadapalli; Amitabh Kumar Jain; Venkata Chalapathi Rao Peddy; Venkateswarlu Choudary Nettem; Sri Ganesh Gandham
Original assignee: Hindustan Petroleum Corp Ltd
Current assignee: Hindustan Petroleum Corp Ltd
Priority date: 2015-10-06
Filing date: 2016-06-30
Publication date: 2018-10-11
Also published as: WO2017060918A1; EP3359630A1

Abstract

A method for preparing a nano suspension lubricant comprises providing substantially spherical nano particles of size ranging from about less than 50 nanometers to about 100 nanometers. The method further comprises mixing the nano particles and a surfactant in about 1:1 ratio in a solvent to form a mixture. The solvent is evaporated from the mixture to obtain surface modified nano particles. The surface modified nano particles include the nano particles coated with the surfactant. The method comprises mixing the surface modified nano particles with a lubricating fluid to form the nano suspension lubricant, where the lubricating fluid comprises about 90% to 99% base oil and about 1% to 10% additives.

Description

TECHNICAL FIELD

The present subject matter relates, in general, to lubricants and, in particular, to nano suspension lubricants.

BACKGROUND

Lubricants play an important role in improving machine life and performance characteristics of a machine. Lubricants are generally used in mechanical components of machines and automobiles to reduce friction and wear. Friction and wear between moving mechanical components of machines and automobiles often result in energy and material losses. Thus, lubricants are used to improve energy efficiency and mechanical durability of the moving mechanical components.
In general, the functions of a lubricant are to: (a) keep surfaces of moving components separated under all loads, temperatures and speeds, thus minimizing friction and wear; (b) act as a cooling fluid removing the heat produced by friction or from external sources; (c) remain adequately stable in order to ensure uniform behavior over the forecasted useful life; and (d) protect surfaces of the moving mechanical components from the attack of corrosive products formed during operation.
In order to meet the various requirements, one or more types of additives or property modifiers are added into a base oil in a lubricant composition. These additives can be, for example, antioxidants, detergents, anti-wear substances, metal deactivators, corrosion inhibitors, rust inhibitors, etc.

BRIEF DESCRIPTION OF DRAWINGS

The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components. For simplicity and clarity of illustration, elements in the figures are not necessarily to scale.

FIG. 1 illustrates a method for preparing a nano suspension lubricant, according to an example implementation.

FIG. 2 graphically illustrates X-ray Diffraction analysis test results for a copper based nano suspension lubricant, according to an example implementation.

FIG. 3(a) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with diesel engine oil as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 3(b) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with diesel engine oil as the lubricating fluid at a load of 60 kgf, according to an example implementation.

FIG. 3(c) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with petrol engine oil as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 3(d) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with petrol engine oil as the lubricating fluid at a load of 60 kgf, according to an example implementation.

FIG. 3(e) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 3(f) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid at a load of 80 kgf, according to an example implementation.

FIG. 3(g) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 3(h) illustrates wear test results for a Molybdenum Disulphide (MoS₂) based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid at a load of 80 kgf, according to an example implementation.

FIG. 4(a) graphically illustrates friction test results indicating the variation in coefficient of friction for the MoS₂based nano suspension lubricant with diesel engine oil as the lubricating fluid, according to an example implementation.

FIG. 4(b) graphically illustrates friction test results indicating the variation in seizure load for the MoS₂based nano suspension lubricant with diesel engine oil as the lubricating fluid, according to an example implementation.

FIG. 4(c) graphically illustrates friction test results indicating the variation in coefficient of friction for the MoS₂based nano suspension lubricant with petrol engine oil as the lubricating fluid, according to an example implementation.

FIG. 4(d) graphically illustrates friction test results indicating the variation in seizure load for the MoS₂based nano suspension lubricant with petrol engine oil as the lubricating fluid, according to an example implementation.

FIG. 4(e) graphically illustrates friction test results indicating the variation in coefficient of friction for the MoS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 4(f) graphically illustrates friction test results indicating the variation in seizure load for the MoS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 4(g) graphically illustrates friction test results indicating the variation in coefficient of friction for the MoS₂based nano suspension lubricant with gear oil of grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 4(h) graphically illustrates friction test results indicating the variation in seizure load for the MoS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 5(a) graphically illustrates extreme pressure (EP) test results indicating the variation in Load wear index (LWI) of the MoS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 5(b) graphically illustrates the extreme pressure (EP) test results indicating the variation in weld load of the MoS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 5(c) graphically illustrates the extreme pressure (EP) test results indicating the variation in Load wear index (LWI) of the MoS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 5(d) graphically illustrates the extreme pressure (EP) test results indicating the variation in weld load of the MoS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 6 graphically illustrates characterization of worn out balls on a scanning electron microscope with X-ray diffraction attachment for the MoS₂based nano suspension lubricant, according to an example implementation.

FIG. 7 graphically illustrates variations in brake thermal efficiency of the MoS₂based nano suspension lubricant in a petrol engine test rig, according to an example implementation.

FIG. 8 graphically illustrates variations in brake thermal efficiency of the MoS₂based nano suspension lubricant in a diesel engine test rig, according to an example implementation.

FIG. 9 graphically illustrates variation in total fuel consumption for the MoS₂based nano suspension lubricant, according to an example implementation.

FIG. 10(a) illustrates wear test results for a Tungsten Disulphide (WS₂) based nano suspension lubricant with diesel engine oil as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 10(b) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with diesel engine oil as the lubricating fluid at a load of 60 kgf, according to an example implementation.

FIG. 10(c) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with petrol engine oil as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 10(d) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with petrol engine oil as the lubricating fluid at a load of 60 kgf, according to an example implementation.

FIG. 10(e) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 10(f) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid at a load of 80 kgf, according to an example implementation.

FIG. 10(g) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with gear oil of grade EP 140 as the lubricating fluid at a load of 40 kgf, according to an example implementation.

FIG. 10(h) illustrates wear test results for the Tungsten Disulphide (WS₂) based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid at a load of 80 kgf, according to an example implementation.

FIG. 11(a) graphically illustrates friction test results indicating the variation in coefficient of friction for the WS₂based nano suspension lubricant with diesel engine oil as the lubricating fluid, according to an example implementation.

FIG. 11(b) graphically illustrates friction test results indicating the variation in seizure load for the WS₂based nano suspension lubricant with diesel engine oil as the lubricating fluid, according to an example implementation.

FIG. 11(c) graphically illustrates friction test results indicating the variation in coefficient of friction for the WS₂based nano suspension lubricant with petrol engine oil as the lubricating fluid, according to an example implementation.

FIG. 11(d) graphically illustrates friction test results indicating the variation in seizure load for the WS₂based nano suspension lubricant with petrol engine oil as the lubricating fluid, according to an example implementation.

FIG. 11(e) graphically illustrates friction test results indicating the variation in coefficient of friction for the WS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 11(f) graphically illustrates friction test results indicating the variation in seizure load for the WS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 11(g) graphically illustrates friction test results indicating the variation in coefficient of friction for the WS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 11(h) graphically illustrates friction test results indicating the variation in seizure load for the WS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 12 graphically illustrates characterization of worn out balls on a scanning electron microscope with X-ray diffraction attachment for the WS₂based nano suspension lubricant, according to an example implementation.

FIG. 13 graphically illustrates variations in brake thermal efficiency of the WS₂based nano suspension lubricant in the petrol engine rig, according to an example implementation.

FIG. 14 graphically illustrates variations in brake thermal efficiency of the WS₂based nano suspension lubricant in the diesel engine rig, according to an example implementation.

FIG. 15 graphically illustrates the variation in total fuel consumption for the WS₂based nano suspension lubricant, according to an example implementation.

FIG. 16(a) graphically illustrates extreme pressure (EP) test results indicating the variation in Load wear index (LWI) of the WS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 16(b) graphically illustrates the extreme pressure (EP) test results indicating the variation in weld load of the WS₂based nano suspension lubricant with gear oil of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation.

FIG. 16(c) graphically illustrates the extreme pressure (EP) test results indicating the variation in Load wear index (LWI) of the WS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

FIG. 16(d) graphically illustrates the extreme pressure (EP) test results indicating the variation in weld load of the WS₂based nano suspension lubricant with gear oil of viscosity grade EP 140 as the lubricating fluid, according to an example implementation.

DETAILED DESCRIPTION

Typically, lubricants are prepared by adding additives to a base oil. Generally, on fractional distillation of crude oil, different base oils separate out as distillates. Examples of base oils are petroleum distillates, mineral oils, vegetable oils, esters, polyolefin, etc. Recently, nano particles have been tested for use as additives in the base oils for lubricants in automobile and other industrial applications. The nano particles may be metals, non-metals, or salts of metals and non-metals having an average particle diameter up to 100 nanometers. Nano particle based lubricants exhibit better tribological properties as compared to ordinary lubricants without nanoparticles. Nanoparticles are considered well suited for tribological applications since lubrication takes place at nano scale level. For instance, certain nano particle molecules can form a thin coating with the thickness of just one or two molecules to separate surface asperities of the moving components of a machine. This may result in better friction resistance between the moving components.
Nano particles have a high surface affinity and chemical reactivity and their small sizes enable them to penetrate into wear crevices. Thus, nano particles are emerging as suitable additives for industrial lubricants, such as, lubricating engine oils, greases, dry film lubricants, and forging lubricants. Several types of nanoparticles have been studied as potential additives for lubricants, including metal oxides of silicon, titanium, nickel, tin, aluminium, and zinc; fluorides of metals such as cerium, lanthanum, and calcium; and zinc, tin, and lead sulfides, and metals, such as nickel, zinc, tin, and silver, and non-metals like carbon nanotubes.
It is generally postulated that rigid spherical and cylindrical nanoparticles dispersed in the base oils protect contacting metal surfaces that are in relative motion from wear by rolling actions, i.e., the nano particles act as miniature ball bearings. However, at higher loads and speeds, the nano particles fall short in the intended lubricating functions. In particular, high wear rates and friction failures remain to be challenging issues for nano particle based lubricants. Thus, nano particles dispersed in base oils are not able to sufficiently provide the intended functions of the nano particle based lubricant.
Better lubricating properties may be obtained when the nano particles are dispersed in lubricating fluids, such as fully formulated lubricants, for example, petrol engine oil of SM grade, diesel engine oil of CI 4 grade, and gear oil GL 4 grade. The lubricating fluids include base oils and other additives, such as, detergents, anti-foaming agents, antioxidants, etc., that have different property modifying effects which make them suitable for use as lubricants. However, there lies a crucial challenge with dispersing the nano particles in the lubricating fluid. On mixing the nano particles in the lubricating fluid, the nano particles have a tendency to agglomerate and settle down after a certain period of time. This results in an unstable solution of the nano particles in the lubricating fluid. Additionally, it is a challenge to obtain a uniform dispersion of the nano particles in the lubricating fluid.
The subject matter described herein relates to a method for preparing a nano suspension lubricant. The nano suspension lubricant described herein includes nano particles dispersed in the lubricating fluid. The lubricating fluid includes a base oil, such as, mineral oils, vegetable oils, esters, etc., and other additives, such as, boron, calcium, etc., that act as antioxidants, anti-wear agents, and the like. In an example implementation, the lubricating fluid may be a fully formulated lubricant, such as, petrol engine oil of SM grade, diesel engine oil CI 4 grade, and gear oil GL 4 grade. The nano suspension lubricant is prepared by mixing surface modified nano particles in the lubricating fluid. As explained later based on test results, the nano suspension lubricant has a greater stability in the lubricating fluid. In an example implementation, surface modification of the nano particles results in the nano particles being coated with an appropriate surfactant selected based on the electrostatic charge of the nano particle and the surfactant that coats on the nano particle. The surface modified nano particles are mixed in the lubricating fluid to form the nano suspension lubricant. The surfactant coated on the surface of the nano particles prevents agglomeration of the nano particles in the lubricating fluid and ensures formation of a stable suspension of the surface modified nano particles in the lubricating fluid. In addition, the nano suspension lubricant obtained on mixing the surface modified nano particles in the lubricating fluid also has better tribological properties, such as, better friction resistance, wear resistance, and an improved brake thermal efficiency, as compared to a conventional nano particle lubricant in which the nano particles are dissolved in a base oil.
Further, tests reveal that there is no deterioration of the physico-chemical properties, such as viscosity index, total acid number, total base number, etc. of the nano suspension lubricant and hence the nano suspension lubricant is suitable for use in the automobile environment.
These and other advantages of the present subject matter would be described in greater detail in conjunction with the following figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter and in no way limit the present subject matter to the description and figures illustrated herein.
FIG. 1 illustrates a method 100 for preparing the nano suspension lubricant, according to an example implementation of the present subject matter. The method 100 for preparing the nano suspension lubricant includes providing substantially spherical nano particles, at block 102. The nano particles may have different structures. For instance, metallic nano particles, such as zinc, tin, copper, tungsten, etc., generally have a substantially spherical structure, while non-metallic nano particles like, tungsten disulphide nano rods and carbon nano tubes have a cylindrical structure with diameters in the nanometric range. The present method includes providing substantially spherical nano particles having an average particle diameter ranging from about less than 50 nanometers to about 100 nanometers. It has been tested that the substantially spherical nano particles over the mentioned range exhibit optimal lubricating properties. Nano particles having a greater particle diameter may tend to wear out the surfaces of the moving mechanical components that are lubricated using the nano suspension lubricant. In an example implementation, the nano particles used for the method 100 may be selected from one of copper, molybdenum disulphide, and tungsten disulphide.
At block 104, the method 100 includes mixing the nano particles and a surfactant in about 1:1 ratio in a solvent to form a mixture. In an example implementation, the solvent may be one of n-hexane, iso octane and toluene. In an example implementation, the solution is stirred in a probe sonicator for about 1 hour for thorough mixing. For stability in a fluid medium, the surface of the nano particles needs to be suitably modified with the surfactant. The surfactants include compounds that lower the surface tension between two liquids or a liquid and a solid and may be used as detergents, anti-foaming agents, and dispersants. Common examples of surfactants include oleic acid, palmitic acid, lauryl alcohol, etc. When the surfactants are mixed with the Nano particles, one end of the surfactant molecule attach to the surface of the nano particle through chemical bonds. The other end of the surfactant molecule is free and extends into the lubricating fluid. Thus, the surfactants generate an effective repulsive force between the nano particles due to steric repulsion between the surfactant molecules attached to the surface of the nano particles. The effective repulsive force between the nano particles coated with the surfactant results in a stable mixture of the nano particles in the lubricating fluid. According to an example implementation, the surfactant may be selected from one of lauric acid, and cetrimonium bromide based on the electronegativity of the surfactant and the type of nano particle on which it is to be coated. In an example implementation, the nano particles and the surfactant are mixed in the solvent by stirring the nano particles and the surfactant in the solvent in an ultra-sound sonicator for about 7 to 8 hours.
At block 106, the method 100 includes evaporating the solvent from the mixture to obtain surface modified nano particles. In an example implementation, the solvent may evaporated at room temperature. On evaporation of the solvent, one end of the surfactant molecule properly bonds to the surface of the nano particles. The surface modified nano particles include the nano particles coated with the surfactant. The surfactant ensures that the surface modified nano particles do not agglomerate when mixed in the lubricating fluid. Thus, a stable dispersion of the surface modified nano particles in the lubricating fluid may be obtained.
At block 108, the method 100 includes mixing the surface modified nano particles with the lubricating fluid. The lubricating fluid includes base oil and additives. In an example implementation, the lubricating fluid includes about 90% to 99% base oil and about 1% to 10% additives. The additives present in the lubricating fluid may include corrosion inhibitors often used in engine coolant like Boron, alkaline or detergent additives, such as magnesium and calcium used to neutralize acids which form during a combustion process in an engine, a friction-reducer and anti-oxidant, such as molybdenum, an anti-foaming agent, such as silicon, and an anti-oxidant and anti-wear agent, such as Zinc dialkyl dithio phosphate (ZDDP). The lubricating fluid contains the above mentioned elements as additives for functioning under severe conditions. In an example implementation, mixing the surface modified nano particles with the lubricating fluid may include sonicating the surface modified nano particles in the lubricating fluid. The sonication may be performed in an ultra-sound sonicator at an amplitude of about 50% and a power of about 200 watts for a duration of about 60 minutes. To obtain optimal results, in an example implementation, the sonication of the surface modified nano particles in the lubricating fluid may be performed in two different modes of sonication. In the example implementation, for 30 minutes the sonication may be performed in pulse mode with 0.5 second pulse. This prevents the agglomeration of the surface modified nano particles. For remaining 30 minutes the sonication is performed in continuous mode which uniformly disperses the surface modified nano particles into the lubricating fluid.
The following discussion is directed to various examples of the present subject matter. Although certain methods and compositions have been described herein as examples, the scope of coverage of this patent application is not limited thereto. On the contrary, the present subject matter covers all methods and compositions fairly falling within the scope of the claims either literally or under the doctrine of equivalents.
Certain terms are used throughout the description to refer to certain components and are to be construed as being mentioned by way of example and for purposes of explanation and not as limiting.
The term “viscosity index” as used in the examples refers to change in viscosity of a lubricant with change in temperature. The lower the viscosity index, the greater is the change of viscosity of a lubricant with temperature. Thus, the higher the viscosity index, the better is the quality of the lubricant. A viscosity index value greater than 90 is preferred for the lubricant.
The term “American Society for Testing and Materials (ASTM) D 445” as used in the examples refers to a test method that specifies a procedure for determination of kinematic viscosity of the lubricant by measuring the time for a volume of liquid to flow under gravity through a calibrated glass capillary viscometer.
The term “total acid number” (TAN) ASTM D 664 as used in the examples refer to a measure of weak organic and strong inorganic acids present in a lubricant. The TAN is the amount of potassium hydroxide in milligrams required to neutralize the acids in one gram of the lubricant. The TAN value indicates potential corrosiveness of the lubricant. A TAN value lesser than 3 indicates that the lubricant is stable.
The term “total base number” (TBN) as used in the examples refers to effectiveness of the lubricant in controlling acid formation during combustion process. The higher the TBN, the more effective the lubricant is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time. A TBN value higher than 9 indicates that the lubricant has good control over acid formation during the combustion process.
The term “ASTM D 2896” as used in the examples refers to a test method for determination of the TBN of the lubricant by potentiometric titration with perchloric acid in glacial acetic acid.
The term “ASTM copper strip corrosion standard as per ASTM D 130” as used in the examples refers to a standard used for representing corrosion protection of the lubricant. The standard has classification numbers from 1 to 4 for various color and tarnish levels of a copper strip immersed in the lubricant. A classification number of 1a indicates excellent corrosion protection, 1b indicates good corrosion protection, and 1c indicates sufficient corrosion protection of the lubricant.
The term “copper strip corrosion test” as used in the examples refers to a test used for determining the classification number of the lubricant. The test involves immersion of a polished copper strip in the lubricant at elevated temperature for a period of time and testing the color and tarnish levels of the copper strip.
The term “four-ball wear test machine” as used in the examples refers to a machine used for testing various performance characteristics of the lubricant. The machine comprises of a ball pot in which three balls are clamped together and thereby kept stationary or fixed in one position. These balls are then covered with the lubricant. A fourth ball is pressed against a cavity formed by the three stationary balls and the fourth ball is rotated.
The term “wear scar diameter” as used in the examples refers to diameter of wear scars on the three stationary balls tested on the four-ball wear test machine. The larger the wear scar, the poorer is the lubricating ability of the lubricant.
The term “ASTM D 4172” as used in the examples refers to a test method for evaluation of the anti-wear properties of the lubricants in sliding contact by means of the Four-Ball Wear Test Machine.
The term “seizure load” as used in the examples refers to a load at which a sudden increase in coefficient of friction value occurs. The higher the seizure load, the better the anti-friction property of the lubricant.
The term “ASTM D 5183” as used in the examples refers to a test method for determining coefficient of friction of the lubricant by means of the Four-Ball Wear Test Machine. Initially, a load is applied which gradually increased at regular time intervals until the lubricant undergoes seizure.
The term “friction test” as used in the examples refers to a test performed for determining the seizure load and the coefficient of friction of the lubricant. The seizure load refers to the load at which there is a sharp rise in fractional torque characterized on a graph while the machine is running. The coefficient of friction is determined by considering the loads between initial load and the seizure load.
The term “ASTM D 2783” as used in the examples refers to a test method for determination of the load-carrying properties of lubricating fluids. The following two determinations are made using ASTM D 2783: 1. Load-wear index, and 2. Weld load by means of the four-ball extreme-pressure tester.
The term “load-wear index” as used in the examples refers to an extreme pressure (EP) property of the lubricant calculated using the four-ball wear test machine Here the speed of rotation is maintained at 1760 RPM and the whole test procedure is done under room temperature. A series of tests of 10-s duration are carried out with increasing loads during each tests until 4 balls weld under extreme pressure. The load at which weld occurs is called the weld load. The first run is made at an initial load of 40 kgf and the additional runs are carried out at consecutively higher loads until and the 4 balls weld under extreme pressure. A total of 10 readings are considered in the test and the corrected load is calculated for all ten readings. The load wear index is calculated from the corrected load. The corrected load is calculated as follows:
Corrected load=LDh/X;
where L is the applied load in kgf, Dh is hertz scar diameter in mm, and
X is average scar diameter in mm.
Hertz scar diameter is the average diameter, in mm, of an indentation caused by deformation of the balls under static load before application of the load. It may be calculated from the equation Dh=8.73×10−3 (P)^1/3.
The term “endurance test” as used in the examples refers to a test conducted on an engine by subjecting it to varying loads and varying speeds for a continuous period of 80 hours without stoppage. This is used to determine the engine wear & tear and fuel consumption over a period of time.
The term “bench test” as used in the examples refers to a test performed on the engine at a particular load and a particular speed to determine the efficiency of the engine at that particular load and speed.
The term “petrol engine rig” as used in the examples refers to a test rig consisting of petrol engine connected to a dynamometer for applying speed and loads to an engine.
The term “diesel engine rig” as used in the examples refers to test rig consisting of diesel engine connected to dynamometer for applying speed and loads to an engine.

EXAMPLES

The following general compositions of nano suspension lubricants, are used in the Examples.

Example 1

Copper Based Nano Suspension Lubricant

In an example implementation, the nano suspension lubricant includes surface modified copper nano particles. The copper nano particles have a particle diameter of less than about 50 nanometers. At this range the copper nano particles used in the nano suspension lubricant gives optimal results. A surface of the copper nano particles is modified using a surfactant to prevent agglomeration of the copper nano particles and to get a uniform dispersion of the copper nano particles in the lubricating fluid. Generally, carboxylate groups attach themselves to metal and metal oxide nano particles making them stable in fluids. The carboxylate groups are soluble in both water as well as oils as they contain both lipophilic and hydrophilic ends. Some of the carboxylate groups mostly used for oil dispersion are lauric acid, stearic acid, and maleic acid. In an example implementation, lauric acid is selected as a surfactant for surface modification of the copper nano particles. The copper nano particles are coated with the lauric acid surfactant to form the surface modified copper nano particles. As a result of the surface modification, the polar head of the lauric acid surfactant attaches to the copper nano particles and the hydrophobic end of the lauric acid surfactant attaches to the oil molecule enabling a stable dispersion of the surface modified copper nano particles in the lubricating fluid. In the example implementation, the surface modified copper nano particles from about 0.05 weight % to 0.1 weight % is dispersed in the lubricating fluid. Mixing the surface modified copper nano particles at the mentioned range gives optimal results for the nano suspension lubricant. Beyond the above mentioned range of weight % of the surface modified nano particles there may be an increase in wear effects on mechanical moving components of an engine where the nano suspension lubricant is being used. This may be due to overcrowding of the surface modified copper nano particles at an interface between the mechanical moving components of the engine in relative motion. In the example implementation, the lauric acid surfactant is mixed in approximately 25.0 ml of n-hexane or toluene solvent by proper stirring to form a mixture. In an example implementation, lauryl alcohol and triton-X may also be used as surfactants. The copper nano particles are added to the mixture and stirred again for 7-8 hours. The n-hexane or toluene solvent is evaporated at room temperature by keeping the mixture undisturbed overnight thus leaving behind the surface modified copper nano particles. The surface modified copper nano particles are coated with the lauric acid surfactant. The surface modified copper nano particles are mixed in the lubricating fluid using an ultra-sound sonicator for 1 hour to achieve a stable suspension of the surface modified copper nano particles in the lubricating fluid.
In an example implementation, the amount of the copper nano particles and surfactant to be mixed in the lubricating fluid to form the stable suspension of the surface modified copper nano particles in the lubricating fluid is given in the following table.

TABLE 1.1

Amount of the copper nano particles and surfactants
used to obtain a stable nano suspension lubricant
according to an example implementation

			Amount of surfactant
		Mass of nano	to be mixed with
	Mass fraction	particles to be	nano particles
	of nano	dispersed in of	and solvent for
Surfactant	particles	lubricant	surface modification

Lauric acid	0.05%	0.45 gm	0.4 gm
	0.1%	0.9 gm	0.8 gm
Lauryl alcohol	0.05%	0.45 gm	12 ml
	0.1%	0.9 gm	20 ml
Triton X-100	0.05%	0.45 gm	12 ml
	0.1%	0.9 gm	24 ml

To test the stability of the copper nano suspension lubricant, an accelerated stability test on a high speed centrifuge has been conducted. In a centrifuge due to the centrifugal action the lighter object move to the top and heavier objects move to the bottom. Different suspensions of nano lubricants made of bare and surface modified nano particles are tested on a centrifuge for accelerated agglomeration of the nano particles under centrifugal action. The centrifugal force applied in the centrifuge tends to bring the nano particles together and agglomerates them. Thus, an uniformly dispersed solvent would remain stable for a longer period of time in the centrifuge.
The following conditions are employed in the test

- Duration of the test 20 mins
- Speed of the centrifuge 10,000 RPM

The test results indicate that when uncoated nano particles are dispersed in the lubricating fluid, the nano particles get agglomerated and settle within the first minute of the test. In an example implementation, the nano suspension lubricant containing 2 mMol of lauryl alcohol as surfactant remains stable for about 10 minutes and the nano suspension lubricant containing 2.5 mMol of lauryl alcohol remains stable for about 20 minutes under the centrifugal action.
Further, tests are also being performed for evaluating changes in Physico-chemical properties, such as, density, viscosity index, total acid number, total base number, sulfonated ash, flash Point, fire point, pour point, etc., of the nano suspension lubricant dispersed with surface modified copper nano particles according to an example implementation of the present subject matter. Any deterioration of the Physico-chemical properties of the nano suspension lubricant below predetermined standards may render the nano suspension lubricant unsuitable for use in automotive environment. The Table 1.2 depicts test results of the physico-chemical properties of the copper based nano suspension lubricant.

TABLE 1.2

Test results of the physico chemical properties of the
copper based nano suspension lubricant

				Base lubricant +	Base lubricant +
SR.		TEST	Base	0.05% nano	0.1% nano
NO.	PROPERTIES	METHOD	lubricant	copper	copper

1	DENITY @ 15 DEG C. g/ml	ASTM D 1298	0.8897	0.8899	0.8912
2	Kinematic Viscosity at 40 deg C., m	ASTM D 445	138.8	135.7	141
	cst
3	Kinematic Viscosity at 100 deg C.,	ASTM D 445	15.68	15.33	15.84
	cst
4	TBN mgKOH/gm	ASTN D 2896	10.4	9.84	10.3
5	TAN mgKOH/gm	ASTM D 664	1.95	1.99	1.93
6	Sulphated Ash %	ASTM D 874	1.43	1.31	1.57
7	Viscosity Index	ASTM D 2270	118	116	117
8	Flash Point, deg C.	ASTM D 92	>190	>190	>190
9	Pour Point, deg C.	ASTM D 97	−24	−24	−24
10	Evaporated Losses (% max 250	ASTM D 5800	5.6	5.7	5.4
	deg C.)
11	Cold Crank Simulator cP @ −20	ASTM D 5293	>12000	>12000	>12000
	deg C.)
12	High Temperature High Shear, cP	ASTM D 4863/	7.9	7.8	8.1
		5481
13	BPT, cP	ASTM D 4863	14	12	18
14	Low temp pumping viscosity, cp	ASTM 4684	>300000	>300000	>300000
15	Copper strip corrosion at 100 deg C.	ASTM D	130	1A	1A	1A
16	Conradson Carbon Residue	ASTM D 189	2.5	2.23	2.78

The test results tabulated in table 1.2 indicate that there is no significant change in the physico-chemical properties of the nano suspension lubricant that may render the nano suspension lubricant unsuitable for use in the automotive environment.
The tribological properties, such as friction resistance, wear resistance, etc., of the copper based nano suspension lubricant is also tested to evaluate improvements in lubricating properties of the nano suspension lubricant. Table 1.3 illustrates the same.
A detailed Tribological analysis and testing is being done as per ASTM G99 standard on a pin on disc tribometer. Prior to conducting the test, the discs are ground in a grinding machine and ensured to be smooth uniformly. The surface roughness is checked for all discs under testing and ensured that they are in the same range (0.2-0.4 μm Ra). This is done to ensure that all the tests are conducted under the same conditions to achieve uniformity.
The test conditions are listed below:

- Load: 5, 10, 15 & 20 kgf
- Speed of rotation: 300, 600, 1200 RPM
- Pin & Disc materials: Cast Iron

TABLE 1.3

Variation in coefficient of friction of the copper based nano suspension
lubricant at a range of increasing speeds at constant loads
Pin on disc results

	% Change from base
Average Coefficient of friction	lubricant

Speed	Base	Cu	Cu	Cu	Cu	Cu	Cu
RPM	lubricant	0.05%	0.1%	0.2%	0.05%	0.1%	0.2%

300	0.0383	0.0342	0.0307	0.0236	10.70	19.84	38.38
600	0.0405	0.0358	0.0332	0.0315	11.60	18.02	22.22
900	0.0466	0.0426	0.0338	0.0334	8.58	27.47	23.33
1200	0.0487	0.0436	0.0366	0.0358	50.47	24.85	26.49

It may be noted from the above table that the copper based nano suspension lubricant exhibits improved friction resistance.

Tribological Testing with ASTM 4 Ball Wear Tester
The wear preventive and anti-friction properties of the lubricants mixed with nano particles are being evaluated using ASTM 4 ball wear tester. As per ASTM D 4172, the wear preventive properties of the nano suspension lubricant can be characterized from the test results tabulated below.

TABLE 1.4

Variation in wear scar diameter with the copper
based nano suspension lubricant

Lubricant	Wear scar in micro meters

Base lubricant	554
Base lubricant + 0.05% Cu nano particles	455
Base lubricant + 0.1% Cu nano particles	432

It may be noted from the wear scar diameter has substantially reduced with increase in the weight % of the surface modified copper nano particles dispersed in the lubricating fluid. This indicates improvement in wear preventive properties of the copper based nano suspension lubricant.
X-Ray Diffraction (XRD) Analysis
Metallographic studies are conducted to assess the reduction in wear due to use of the nano suspension lubricant according to an example implementation. After conducting wear tests, the balls of wear test are subjected to XRD analysis for analysis of the possible deposition of the copper nano particles on surfaces of the worn balls. FIG. 2 graphically illustrates the XRD analysis test results for the copper based nano suspension lubricant according to an example implementation. The graph 200 shown in FIG. 2 depicts the amount of deposition of the copper nano particles present in the nano suspension lubricant onto the worn out surfaces of the metallic balls. In x-axis a diffraction angle of the X-ray diffraction is plotted and in the y-axis the amount of deposition of the copper nano particles on the surface of the worn our metallic balls is depicted. The diffraction angle is measured in degrees and the amount of deposition is expressed in an arbitrary unit of number of cycles of measurement in the XRD. From the FIG. 2 it may be noted that along with iron (Fe), Nickel (Ni), Chromium (Cr) and oxygen (O) copper (Cu) can also be seen at peaks of the graph 200. This suggests deposition of the copper nano particles on the surface of the worn out balls and form a protective coating thereby offering resistance to wear.
Friction Test as Per ASTM D 5183 Standard
The friction test has been conducted to determine the coefficient of friction of the copper based nano suspension lubricant under the following prescribed test conditions using the ASTM 4 Ball wear tester.
The test is conducted under the following test conditions:

- Temperature 75±2° C.
- Speed 600 RPM
- Duration 10 min at each load starting from 10 kgf
- Load 98.1 N (10 kgf) per 10 min increment to a load that indicates incipient seizure, i.e., sudden increase in friction force value over steady state on the friction trace.

TABLE 1.5

Variation in coefficient of friction of the copper based nano
suspension lubricant with increasing loads at a constant speed
Oil

		coefficient
oil	seizure load	of friction

Base lubricant

	120	0.11
Base lubricant + 0.05% Cu nano particles	140	0.095
Base lubricant + 0.1% Cu nano particles	150	0.088

Thus, the test results depicted in the Table 1.5 suggest that the coefficient of friction decreases with increase in the surface modified copper nano particles dispersed in the lubricating fluid and thus at 0.1 weight % of the surface modified copper nano particles dispersed in the lubricating fluid the results are optimum.
Tests Conducted on Roller Test Bench
Tests have been done using roller test bench with a two-wheeler mounted on it. Hydraulic load is applied on the rollers of the test bench and the rollers in turn apply braking action on the rear wheel. Tests were carried out with the lubricating fluid without nano particles and the lubricating fluid mixed with 0.05 weight % & 0.1 weight % of the surface modified copper nano particles. The hydraulic loading is done by means of water forcing through a dynamometer at a particular pressure. The pressure may be regulated by operating a gate valve. To increase or decrease the load, the gate valve is opened or closed thereby regulating the pressure. The tests were carried out at constant speeds of 40, 50 & 50 KMPH at various gate openings of the dynamometer. The initial gate opening is fixed at 40 KMPH and 2 kgf, 3 kgf & 4 kgf load respectively and the speed is increased with a corresponding increase in load.
The rated brake power of the engine is 5.733 kW (7.8 HP) and the testing was carried out up to a maximum load 8 kgf @ 60 KMPH which corresponds to 3.5 kW of brake power or 62% of Maximum brake power. The following sample results compare the results of the lubricating fluid and lubricating fluid mixed with the surface modified copper nano particles. From the results tabulated below it can be observed that when the two-wheeler uses the lubricating fluid mixed with surface modified copper nano particles better mileage and brake thermal efficiency is obtained.

TABLE 1.6

Test results for roller test bench with the copper based nano suspension lubricant

								% Change
	SPEED	MILEAGE	LOAD	N	Brake	tfc		From base
	(KM/HR)	(KM/LITRE)	(KG)	RPM	power kW	kg/hr	η_bth	lubricant

Lubricating fluid	40	82.75	2.01	786.35	0.582	0.358	13.01
Lubricating fluid +	40	93.91	2.03	786.35	0.587	0.315	14.90	13.48
0.05% surface modified
Cu nano particles
Lubricating fluid +	40	88.13	2.02	786.35	0.585	0.336	13.94	6.5
0.1% surface modified
Cu nano particles
Lubricating fluid	40	76.23	3.01	786.35	0.869	0.388	17.91
Lubricating fluid +	40	79.01	3.03	786.35	0.876	0.375	18.70	3.64
0.05% surface modified
Cu nano particles
Lubricating fluid +	40	81.85	3.06	786.35	0.883	0.362	19.54	7.34
0.1% surface modified
Cu nano particles
Lubricating fluid	40	63.51	4.08	786.35	1.178	0.466	20.22
Lubricating fluid +	40	64.48	4.03	786.35	1.163	0.459	21.01	1.5
0.05% surface modified
Cu nano particles
Lubricating fluid +	40	70.29	4.05	786.35	1.171	0.421	22.25	10.67
0.1% surface modified
Cu nano particles

	SPEED	MILEAGE	LOAD	N	Brake	tfc		%
	(KM/HR)	(KM/LITRE)	(KG)	RPM	power kW	kg/hr	η_bth	change

Lubricating fluid	50	69.05	2.73	982.94	0.987	0.536	14.73
Lubricating fluid +	50	77.73	2.77	982.94	1.002	0.476	16.84	12.57
0.05% surface modified
Cu nano particles
Lubricating fluid +	50	78.49	2.80	982.94	1.010	0.472	17.14	13.67
0.1% surface modified
Cu nano particles
Lubricating fluid	50	61.03	4.32	982.94	1.562	0.606	20.61
Lubricating fluid +	50	65.53	4.30	982.94	1.552	0.566	21.98	7.37
0.05% surface modified
Cu nano particles
Lubricating fluid +	50	67.94	4.30	982.94	1.552	0.545	22.79	11.32
0.1% surface modified
Cu nano particles
Lubricating fluid	50	50.81	6.00	982.94	2.168	0.729	23.82
Lubricating fluid +	50	53.06	5.93	982.94	2.140	0.698	24.54	4.42
0.05% surface modified
Cu nano particles
Lubricating fluid +	50	56.54	5.97	982.94	2.158	0.655	26.38	11.27
0.1% surface modified
Cu nano particles
Lubricating fluid	60	50.75	4.15	1179.52	1.801	0.875	16.47
Lubricating fluid +	60	65.34	4.04	1179.52	1.753	0.680	20.62	16.27
0.05% surface modified
Cu nano particles
Lubricating fluid +	60	65.66	4.09	1179.52	1.772	0.677	20.96	22.34
0.1% surface modified
Cu nano particles
Lubricating fluid	60	39.69	6.04	1179.52	2.618	1.119	18.72
Lubricating fluid +	60	41.83	6.04	1179.52	2.619	1.063	19.74	5.44
0.05% surface modified
Cu nano particles
Lubricating fluid +	60	46.67	6.02	1179.52	2.607	0.954	21.93	17.16
0.1% surface modified
Cu nano particles

Lubricating fluid

* the bike could not run at this speed and load with the lubricating fluid

Lubricating fluid +	60	32.73	8.00	1179.52	3.466	1.363	20.44
0.05% surface modified
Cu nano particles
Lubricating fluid +	60	39.93	8.09	1179.52	3.508	1.121	25.24
0.1% surface modified
Cu nano particles

It can be noted from the table 1.6 that at lower loads and speeds, the percentage change in brake thermal efficiency is medium and at higher loads and speeds it is quite high. It is also observed that the lubricating fluid mixed with 0.1 weight % of the surface modified copper nano particles gives best mileage at all loads and speeds. It can be inferred that the optimum amount of the surface modified copper nano particles to be added to the lubricating fluid for best performance of the two-wheeler corresponds to 0.1 weight %. Further increase in the weight % of the surface modified copper nano particles in the lubricating fluid, may increase viscous effects of the copper based nano suspension lubricant thereby increasing pumping losses of the engine and hence decreasing mileage of the engine.
Test for Deceleration of the Two-Wheeler
The friction in moving parts of an engine of the two-wheeler is directly related to acceleration and deceleration of the two-wheeler. A high acceleration and low deceleration of the two-wheeler infers lesser friction in the moving parts. The test method of assessing the reduction in friction of the moving parts is being done by noting the acceleration and deceleration of the two-wheeler. The two-wheeler is accelerated to 60 KMPH speed and the power of the two-wheeler is switched off. The time required by the two-wheeler to decelerate from 60 KMPH to 0 KMPH is noted down. The results are tabulated below.
TABLE 1.7

Variation in deceleration time with the copper

based nano suspension lubricant

Deceleration time in seconds

Base lubricant +

0.05% cu nano Base lubricant +

Load Base lubricant particles 0.1% cu nano particles

2 8.21 secs 8.58 9.51

3 6.86 7.25 8.15

4 6.56 6.88 7.10

It may be observed from Table 1.7 that the copper based nano-suspension lubricant has taken more time for deceleration than the lubricating fluid without any nano particle dispersed in it. This suggests that the friction in the moving parts of the two-wheeler while using the copper nano suspension lubricant is less and thus loss of energy due to friction is reduced.
Field Test on Actual Road Conditions
Field tests have been conducted in actual road conditions at different speeds and different loads on the two-wheeler. 10 observations were made at each load and speed taking a sample of 250 ml of petrol in each observation. The results of the test are tabulated below.
Acceleration (Pickup) of the Two-Wheeler in Road Conditions with 160 kg Load (2 Persons)
TABLE 1.8

Variations in acceleration time with copper

based nano suspension lubricant

Acceleration time is seconds (0-60 KMPH)

With base lubricant 6.12 s

Acceleration with base lubricant + 0.05% cu nano particles 5.65 s

Acceleration with base lubricant + 0.1% cu nano particles 5.34 s

From table 1.8 it may be observed that the acceleration time has reduced and hence the pickup of the two-wheeler has increased. There has also been observed substantial increase in mileage of the two-wheeler with use of the copper based nano suspension based lubricant. The test results illustrating the same have been tabulated below in table 1.9.

TABLE 1.9

Variations in mileage with copper based nano suspension lubricant
Results of tests done in actual road conditions

	40 and		40 and
	160 kgs load	% increase		80 kgs load	% increase	50	% increase
Oil
	2 person)	in mileage	(1 person)	in mileage	(2 persons)	in mileage

Base lubricant	72-75		76-80		68-40
Base lubricant +	73-77	2.04%	78-82	2.56%	70-74	4.34%
0.05% nano
particles
Base lubricant +	76-84	8.84%	80-88	7.70%	74-80	11.60%
0.1% nano
particles

	50	% increase	60	% increase	60	% increase
Oil	(1 person)	in mileage	(2 persons)	in mileage	(1 persons)	in mileage

Base lubricant	71-73		53-55		54.56
Base lubricant +	74-78	5.55%	59.66	15.74%	60-67	15.45%
0.05% nano
particles
Base lubricant +	76-82	9.72%	60-66	16.60%	61-67	16.30%
0.1% nano
particles

indicates data missing or illegible when filed

Exhaust Gas Analysis on Four Stoke Bike
A typical exhaust gas analysis on a 4 stroke bike with the copper based nano suspension lubricant is presented in the table 1.10.

TABLE 1.10

Variations in emission properties for the copper
based nano suspension lubricant
Results of Exhaust gas analysis

Lubricant	CO	CO2	HC	NOX

Bass lubricant	2.587%	8.36%	485 PPM	71 PPM
Base lubricant + 0.05% Cu	2.873%	7.01%	446 PPM	28 PPM
Bass lubricant + 0.1% Cu	2.672%	7.15%	489 PPM	15 PPM

From table 1.10 it may be noted that the emission of poisonous gases such as, CO₂, HC and NOX are substantially reduced when the lubricating fluid is mixed with the surface modified copper nano particles.

Example 2

MoS₂Based Nano Suspension Lubricant

The nano suspension lubricant described herein can be based on a number of different exemplary compositions. In example 1, metallic copper can be used as a nano particle to be dispersed into the lubricating fluid. Likewise, metallic sulphides such as, molybdenum sulphide is used as a nano particle in the nano suspension lubricant. Typically, the surfactants used for modifying the surface of the metallic sulphides are cationic surfactants. The cationic surfactant molecules carry a positive charge at the hydrophilic end of the surfactant molecule. Examples of cationic surfactants include quaternary ammonium salts, cetrimonium bromide (CTAB), etc. Thus, according to an example implementation of the present subject matter, the nano suspension lubricant includes surface modified molybdenum disulphide nano particles from about 0.05 weight % to 0.1 weight % dispersed in the lubricating fluid. The lubricant fluid includes about 90% to 99% base oil, such as, petroleum fractions, mineral oils, vegetable oils, synthetic oils, solvent refined mineral oils, hydrocracked mineral oils, polyalphaolefins, polyalkylglycols, synthetic esters, and the like. The lubricating fluid also includes about 1% to 10% additives, such as, antioxidants, detergents, and antiwear agents. The molybdenum disulphide (MoS₂) nano particles are coated with sorbitan monooleate surfactant in a similar method as employed for coating the copper nano particles with lauric acid in the example 1 to obtain surface modified MoS₂nano particles. The surface modified molybdenum disulphide nano particles from about 0.05 weight % to 0.1 weight % are dispersed in the lubricating fluid by stirring for about 1 hour in an ultra sound sonicator. The MoS₂nano particles used have a size less that about 100 nanometers. In an example, Silane can be used for being coated on the MoS₂nano particles for surface modification of the MoS₂nano particles.
Evaluation of Stability of Lubricating Oil Suspension Containing the Surface Modified MoS₂Nano Particles Using Light Scattering Techniques
Dynamic light scattering (DLS) is a technique used to determine the size distribution profile of small particles in suspension or polymers in a mixture. The stability of any suspension is measured in terms of relative change in average particle size of the dispersed particles in the suspension. In a good suspension the size of the particles remain more or less same over a period of time. The stability of the surface modified MoS₂nano particles in lubricating fluid is tested using DLS. The stability of the suspension in terms of average particle size is investigated over a period of 2 months. The variation of the MoS₂nano particles surface modified with Sorbitan Monooleate is shown in the following table.
TABLE 2.1

The average particle size of the surface modified

MoS₂nano particles over a period of 60 days

Average particle size of surface

modified MoS₂nano particles

Day expressed in nanometers (nm)

1^stDay 308.1

15^thDay 293.3

30^thDay 376.8

60^thDay 392.2

As may be understood from the table 2.1, the average particle size of the surface modified MoS₂nano particles over a period of 60 days did not have substantial change. This indicates good steric repulsions between the surface modified MoS₂nano particles. Thus, in case of MoS₂nano particles, the Sorbitan Monooleate keeps the suspension of the modified MoS₂nano particles in the lubricating fluid stable.
In an example implementation, the MoS₂based nano suspension lubricant described herein can be used for lubrication in vehicles the automotive industry. Thus, to determine the suitability of the MoS₂based nano suspension lubricant in the automotive industry evaluation of physico chemical properties of the MoS₂based nano suspension lubricant becomes necessary. The physico-chemical properties of a lubricant include viscosity index, total acid number, total base number of a nano suspension lubricant that determine the suitability of the nano suspension lubricant for use in vehicles, such as in engines of two-wheelers and four-wheelers. In particular, the physico-chemical properties of the nano suspension lubricants are evaluated to investigate the suitability of the surfactant and the surface modification process to the automotive environment.
Further, a nano suspension lubricant exhibits different physico-chemical properties depending on a kind of base oil used in the lubricating fluid. Accordingly, test results are illustrated below for the MoS₂based nano suspension lubricant including lubricating fluids having different compositions for the base oil.
Tests for Physico-Chemical Properties
In an example implementation to analyze the physico-chemical properties of the MoS₂based nano suspension lubricant, different tests such as Kinematic viscosity test, total acid number test, total base number test, and copper strip corrosion test are performed.
Kinematic Viscosity Test
Viscosity of the nano suspension lubricant is closely related to its ability to reduce friction. Viscosity index is a parameter that indicates the variation of viscosity with temperature. The Viscosity index is calculated as per ASTM D 445 standard by measuring viscosity of the MoS₂based nano suspension lubricant at 40° C. and 100° C. A high value (normally >90) of the viscosity index indicates that the nano suspension lubricant has good lubricating properties.

TABLE 2.2

Viscosity index for the MoS₂based nano suspension lubricant with
SM petrol engine oil (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Viscosity index

	Petrol engine oil SM grade	>110
	(SAE 20 W 40) + 0.05 MoS₂
	Petrol engine oil SM grade	>110
	(SAE 20 W 40) + 0.1 MoS₂

TABLE 2.3

Viscosity index for the MoS₂based nano suspension lubricant with
diesel engine oil CI 4 grade (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Viscosity index

	Diesel engine oil CI 4 (SAE	>110
	15 W 40) + 0.05 MoS₂
	Diesel engine oil CI 4 (SAE	>110
	15 W 40) + 0.1 MoS₂

Total Acid Number Test
Total Acid Number (TAN) is a measure of presence of acids within the nano suspension lubricant. The Total Acid Number is the amount of potassium hydroxide in milligrams that is needed to neutralize the acids in one gram of the nano suspension lubricant. The TAN value indicates potential corrosiveness of the nano suspension lubricant. Thus, maintaining a low TAN value is essential to maintain and protect components of engines. Generally, a low TAN value (<3) gives an indication that the nano suspension lubricant is non-corrosive. The table below illustrates the TAN values of the MoS₂based nano suspension lubricant including surface modified MoS₂nano particles dispersed in different lubricating fluids having different base oil compositions.

TABLE 2.4

Total Acid number with MoS₂based nano suspension
lubricant having petrol engine oil SM grade
(SAE 20 W 40) as the lubricating fluid

	Lubricant used	Total Acid number

	Petrol engine oil SM grade (SAE	<2
	20 W 40)
	Petrol engine oil SM grade (SAE	<2
	20 W 40) + 0.05 MoS₂
	Petrol engine oil SM grade (SAE	<2
	20 W 40) + 0.1 MoS₂

TABLE 2.5

Total Acid number with MoS₂based nano suspension
lubricant having diesel engine oil CI4 grade
(SAE 15 W 40) as the lubricating fluid

	Lubricant used	Total Acid number

	Diesel engine oil CI4 grade (SAE	<2.2
	15 W 40)
	Diesel engine oil CI4 grade (SAE	<2.2
	15 W 40) + 0.05 MoS₂
	Diesel engine oil CI4 grade (SAE	<2.2
	15 W 40) + 0.1 MoS₂

Thus, as may be understood from the tables above, the Total Acid Number of the nano suspension lubricant dispersed with surface modified MoS₂nano particles does not result in substantial change or deterioration of the total acid number of the nano suspension lubricant and is suitable for use in the automotive industry.
Total Base Number Test
The nano suspension lubricant is required to prevent acidic corrosion within the combustion chamber of a running engine and should protect different engine components, such as, piston rings, cylinder liner and piston crown from damage by sulphur or nitrogen containing acids. The Total Base Number (TBN) of the nano suspension lubricant determines how effectively acids formed during combustion process of the engine are reduced. The higher the TBN (typically >9), the more effective the nano suspension lubricant is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time. Typically, the TBN of the nano suspension lubricant is measured by the ASTM D 2896 standard potentiometric titration with perchloric acid. The TBN of the nano suspension lubricant may vary depending on the different kinds of lubricating fluid that is being used. For example, depending on the composition of the lubricating fluid, i.e., the kind of base oil and additives used in the lubricating fluid, the TBN of the nano suspension lubricant may differ. The tables below illustrate the TBN values of the MoS₂based nano suspension lubricant including surface modified MoS₂nano particles dispersed in different lubricating fluids having different base oil compositions.

TABLE 2.6

Total Base number with the MoS₂based nano suspension
lubricant having diesel engine oil CI4 grade
(SAE 15 W 40) as the lubricating fluid

	Lubricant used	Total Base number

	Diesel Engine oil CI4 grade	>10
	Diesel Engine oil CI4 grade + 0.1%	>10
	surface modified MoS₂nano particles
	with surfactant SPAN 80
	Diesel Engine oil CI4 grade + 0.1%	>10
	surface modified MoS₂nano particles
	with surfactant Silane

TABLE 2.7

Total Base number with MoS2 nano suspension lubricant having petrol
engine oil SM grade (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Total Base number

	Petrol engine oil	>6
	Petrol engine oil + 0.1% surface modified	>6
	MoS₂nano particles with surfactant
	SPAN
80
	Petrol engine oil + 0.1% surface	>6
	modified MoS₂nano particles with
	surfactant Silane

Copper Strip Corrosion Test
The Copper Strip Corrosion Test is carried out to assess the relative degree of corrosiveness of a number of petroleum products, including aviation fuels, automotive gasoline, lubricating oils and other products. Hence, the copper strip corrosion test is performed for the MoS₂based nano suspension lubricant. In the test, a classification number from 1-4 is assigned based on a comparison with the ASTM Copper Strip Corrosion Standards. A value of 1a, 1b, and 1c indicates corrosion protection provided by the MoS₂based nano suspension lubricant under test. Further, it may be understood by a person skilled in the art that the value of 1a denotes excellent protection, 1b denotes good protection, and 1c denotes sufficient protection provided by the MoS₂based nano suspension lubricant.
In these tests, the petrol engine oil of SM 4 grade is selected as the lubricating oil. The lubricating oil mixed with MoS₂was tested for copper strip corrosion test at 100° C. for 3 hours and their tarnish level was assessed against the ASTM Copper Strip Corrosion Standard.
The results are shown in the table below.

TABLE 2.8

Copper strip corrosion test results for
the MoS₂based nano suspension lubricant

Lubricant used	Copper strip corrosion result

Petrol engine oil of SM grade	1a
Petrol engine oil of SM grade +	1a
surface modified MoS₂nano particles
using surfactant sorbitan monooleate
Petrol engine oil of SM grade +	1b
surface modified MoS₂nano particles
using surfactant Silane

From the above test results of the physico-chemical properties of the MoS₂based nano suspension lubricant, it may concluded that the surface modified MoS₂nano particles have no substantial effect on the total acid number and the total base number of the MoS₂based nano suspension lubricant. Thus, it may concluded that there is no abnormal deterioration of the physico-chemical properties of the MoS₂based nano suspension lubricant and hence the MoS₂based nano suspension lubricant is suitable for the automotive environment.
Further, in order to assess the tribological properties, such as friction resistance, wear resistance, etc., of the nano suspension lubricant, wear and friction tests are performed on the MoS₂based nano suspension lubricant. The wear and friction tests are conducted for the surface modified MoS₂nano particles dispersed in different lubricating fluids.
Four Ball Wear Test
The Four Ball Wear Test determines the wear protection properties of a lubricant. The wear tests are conducted for each of petrol engine oil and diesel engine oil as the lubricating fluid at 40 kgf load and 60 kgf load. The wear tests on gear oils of GL 4 grade are conducted at 40 kgf and 80 kgf loads. The wear scar diameters (WSD) on the stationary balls were measured using a Metallurgical microscope.
FIGS. 3(a)-3(h) illustrate the wear test results for the MoS₂based nano suspension lubricant with the surface modified MoS₂nano particles suspended in different lubricating fluids, according to an example implementation. In the graphs illustrated in the FIGS. 3(a)-3(h), the y-axis depicts the wear scar diameter and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant with different lubricating fluids, such as diesel engine oil, petrol engine oil, and gear oil. The wear scar diameter is represented in microns.
The graph 300(a) illustrated in FIG. 3(a) depicts the wear test results of the MoS₂based nano suspension lubricant having diesel engine oil of CI 4 grade as the lubricating fluid at 40 Kgf load, according to an example implementation. It may be noted from the graph 300(a) that the wear scar diameter is greater without the MoS₂nano particles dispersed in the lubricating fluid and on mixing the MoS₂nano particles in the lubricating fluid the wear scar diameter substantially reduces.
The graph 300(b) illustrated in FIG. 3(b) depicts the wear test results of the MoS₂based nano suspension lubricant having diesel engine oil of CI 4 grade as the lubricating fluid at 60 Kgf load, according to an example implementation. It may be noted that minimum wear scar diameter or in other words, maximum wear protection is possible when the lubricating fluid is mixed with 0.1 weight % of MoS₂nano particles.
The graph 300(c) illustrated in FIG. 3(c) depicts the wear test results of the MoS₂based nano suspension lubricant having petrol engine oil of SM grade as the lubricating fluid at 40 Kgf load, according to an example implementation. It may be noted that optimum wear protection is possible when 0.1 weight % of MoS₂nano particles is mixed in the lubricating fluid.
The graph 300(d) illustrated in FIG. 3(d) depicts the wear test results of the MoS₂based nano suspension lubricant having petrol engine oil of SM grade as the lubricating fluid at 60 Kgf load, according to an example implementation. Again, minimum wear scar diameter at 0.1% MoS₂is mixed in the lubricating fluid.
The wear properties of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade as the lubricating fluid are also tested. The gear oil of GL 4 grade having two different viscosity grades, such as EP 140 and SAE 80 W 90 have been used for the tests. The graph 300(e) illustrated in FIG. 3(e) depicts the wear test results of MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade SAE 80 W 90 as the lubricating fluid at 40 Kgf load, according to an example implementation. The gear oil having 0.1% of MoS₂nano particles dispersed in it shows optimal results with minimum scar diameter. The graph 300(f) illustrated in FIG. 3(f) depicts the wear test results of MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade SAE 80 W 90 as the lubricating fluid at 80 Kgf load, according to an example implementation. As can be seen from the graph 300(f), the gear oil having 0.05% of MoS₂nano particles dispersed in it shows optimal results with minimum wear scar diameter value of 512.42.
The graph 300(g) illustrated in FIG. 3(g) depicts the wear test results of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade EP 140 as the lubricating fluid at 40 Kgf load, according to an example implementation. The gear oil mixed with the MoS₂nano particles shows substantial improvement in wear protective properties, as can be understood from the graph 300(f).
The graph 300(h) illustrated in FIG. 3(h) depicts the wear test results of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade EP 140 as the lubricating fluid at 80 Kgf load, according to an example implementation.
From the above graphical illustrations it may be concluded that based on the lubricating oil an optimum weight percentage of the nano particles may be chosen for best performance. As may be observed from the graphs, in general, the optimum weight % of the surface modified MoS₂nano particles for best results lies between 0.05% to 0.1%.
Further, to determine the tribological properties of the MoS₂based nano suspension lubricant friction tests as per ASTM D 5183 standard have been performed. The frictions tests have been conducted to determine the coefficient of friction of the MoS₂based nano suspension lubricant under the following prescribed test conditions using ASTM 4 Ball wear test machine.


Temperature	75 ± 2° C.
Speed
	600 RPM
Duration
	10 min at each load starting from 10 kgf
Load	98.1N (10 kgf) per 10 min increment to a load that indicates
	incipient seizure (sudden increase in friction force value
	over steady state) on the friction trace

FIGS. 4(a)-4(h) graphically illustrate the friction test results for the MoS₂based nano suspension lubricant with the surface modified MoS₂nano particles suspended in different lubricating fluids, according to an example implementation. In the graphs 400(a), 400(c), 400(e), and 400(g) illustrated in the FIGS. 4(a), 4(c), 4(e), and 4(g) the y-axis depicts the coefficient of friction of the MoS₂based nano suspension lubricants and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant with varying percentages of the MoS₂nano particles dispersed in the lubricating fluid. In the graphs illustrated in 400(b), 400(d),400(f), and 400(h) the y-axis depicts seizure load and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant with varying percentages of the MoS₂nano particles dispersed in the lubricating fluid.
The graph 400(a) illustrates the variations in the coefficient of friction in MoS₂based nano suspension lubricant having diesel engine oil of CI 4 grade as the lubricating fluid, according to an example implementation. It may be noted from the 400(a) that the coefficient of friction of the lubricating fluid, i.e., CI 4 grade diesel engine oil is greater without the MoS₂nano particles and on mixing the surface modified MoS₂nano particles in the lubricating fluid the coefficient of friction substantially reduces. This reduces the frictional force between the moving mechanical components in the engine.
The graph 400(b) illustrates the variations in seizure load of the MoS₂based nano suspension lubricant having diesel engine oil of CI 4 grade as the lubricating fluid, according to an example implementation. It may be noted that when the lubricating fluid, i.e., diesel engine oil of CI 4 grade in this case, is mixed with 0.05% of the surface modified MoS₂nano particles, the nano suspension lubricant can endure a maximum seizure load of up to 140 Kgf.
The graph 400(c) illustrates the variations in the coefficient of friction in the MoS₂based nano suspension lubricant having petrol engine oil of SM grade as the lubricating fluid, according to an example implementation. It may be noted, that the nano suspension lubricant having 0.05% of the surface modified MoS₂nano particles dispersed in the lubricating fluid has a minimum coefficient of friction value of 0.0908. Thus, it may be concluded that the mentioned composition has optimal friction resistance properties.
The graph 400(d) illustrates the variations in seizure load of the MoS₂based nano suspension lubricant having petrol engine oil of SM grade as the lubricating fluid, according to an example implementation. The graph 400(d) depicts that the MoS₂based nano suspension lubricant having 0.05% of the surface modified MoS₂nano particles dispersed in the lubricating fluid can endure a maximum seizure load of up to 140 Kgf.
In an example, a lubricating oil such as gear oil of GI 4 grade oil having two different viscosity grades, such as EP 140 and SAE 80 W 90 have been used for the tests. The graph 400(e) illustrates the variations in the coefficient of friction in the MoS₂based nano suspension lubricant having gear oil of GL 4 grade of viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation. The gear oil having 0.05% of the surface modified MoS₂nano particles dispersed in it shows optimal results with a minimum value of friction coefficient of 0.071. The graph 400(f) illustrates the variations in seizure load of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade SAE 80 W 90 as the lubricating fluid, according to an example implementation. As can be seen from the graph 400(f), the gear oil having 0.05% of the surface modified MoS₂nano particles and 0.1% of the surface modified MoS₂nano particles dispersed in the lubricating fluid can endure a maximum seizure load of up to 160 Kgf.
The graph 400(g) illustrates the variations in the coefficient of friction in the MoS₂based nano suspension lubricant having gear oil of GL 4 grade of viscosity grade EP 140 as the lubricating fluid, according to an example implementation. The gear oil mixed with the MoS₂nano particles shows substantial improvement in friction protective properties, as can be understood from the graph 400(g). A minimum coefficient of friction value of 0.071 is observed for 0.05% of the surface modified MoS₂nano particles mixed in the lubricating fluid, i.e., the gear oil.
The graph 400(h) illustrates the variations in seizure load of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade of viscosity grade EP 140 as the lubricating fluid, according to an example implementation. As can be seen from the graph 400(h) the gear oil having 0.05% of the surface modified MoS₂nano particles dispersed in the gear oil can endure a maximum seizure load of up to 160 Kgf.
Thus, from the above friction test results it may be concluded that the MoS₂based nano suspension lubricant evidences substantially improved friction properties with endurance over higher seizure loads. Further, for optimum results the surface modified MoS₂nano particles between 0.05 weight % to 0.1 weight % can be mixed in the lubricating fluid.
Extreme pressure lubricants, such as gear oils are designed for use in severe applications across a variety of conditions, including high load, moisture and a wide range of operating speeds and loads. Thus, extreme pressure (EP) properties of the MoS₂based nano suspension lubricant with the gear oil as the lubricating fluid are tested.
Evaluation of EP Properties of the Nano Suspension Lubricant Using ASTM D 2783 Standard
The EP test determines the load carrying properties of the nano suspension lubricant. Generally, two parameters, such as Load-wear index and Weld load are evaluated to make this determination. Higher the value of the load wear index and weld load for a lubricant, the lubricant may be understood to have better EP properties.
The EP tests are carried out on the MoS₂based nano suspension lubricant having Gear oils of GL4 grade of viscosity grade SAE 80 W 90 and EP 140 as the lubricant fluid.
FIGS. 5(a)-5(d) graphically illustrates the variation of extreme pressure (EP) properties of the MoS₂based nano suspension lubricant, according to an example implementation. The results of Table 2.13 are plotted in the graphs 500(a) and 500(b) illustrated in FIGS. 5(a) and 5(b), respectively. The graph 500(a)) depicts the variation in Load wear index of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade of SAE 80 W 90 as the lubricating fluid. The y-axis of the graph 500(a) illustrated in FIG. 5(a) depicts the load-wear index and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant, varying in the weight % of the surface modified MoS₂nano particles mixed in the lubricating fluid. The graph 500(b) depicts the variation in weld load of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade of SAE 80 W 90 as the lubricating fluid, according to an example implementation. The y-axis of the graph 500(b) represents the weld load and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant, varying in the weight % of the surface modified MoS₂nano particles mixed in the lubricating fluid. The weld load is represented in Kgf.
The graph 500(c) illustrates the variation in Load wear index of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade of EP 140 as the lubricating fluid, according to an example implementation. The results of the Table 2.14 are plotted in the graphs 500(c) and 500(d). The y-axis of the graph 500(c) depicts the load-wear index and the x-axis depicts different compositions of the MoS₂based nano suspension lubricant. The graph 500(d) depicts the variation in weld load of the MoS₂based nano suspension lubricant having gear oil of GL 4 grade with viscosity grade of EP 140 as the lubricating fluid, according to an example implementation. It may be noted that with addition of the surface modified MoS₂nano particles from 0.5 weight % to 0.1 weight % into the lubricating fluid, the weld load characteristics have substantially improved. Particularly, it may be noted that on mixing 0.1 weight % of the surface modified MoS₂nano particles in the lubricating fluid, the lubricant can endure a weld load as high as 280 Kgf.
Further, to determine the wear characteristics of the MoS₂based nano suspension lubricant, metallographic studies of worn out metallic balls used in the wear test can be performed. The scar area of the worn out metallic balls after the wear test are magnified in a Scanning Electron Microscope (SEM) and observed for deposition of particles on the worn out surface of the balls. On viewing the balls in the SEM deposition of nano particles on the surface of the worn out balls can be seen. FIG. 6 illustrates characterization of the worn out balls on scanning electron microscope with X-ray diffraction attachment, according to an example implementation.
The graph 602 in FIG. 6 depicts the deposition of particles on the worn out balls when the lubricating fluid, such as gear oil GL 4 grade is being used. The graph 604 depicts the deposition of particles on the worn out balls when the lubricating fluid, such as gear oil of GL 4 grade mixed with 0.05 weight % of the surface modified MoS₂nano particles is being used for lubrication. The graph 606 depicts the deposition of particles on the worn out balls when the lubricating fluid, such as gear oil GL 4 grade mixed with 0.10 weight % of the surface modified MoS₂nano particles is being used for lubrication. The y-axis of the graphs 602, 604, and 606 depict the amount of deposition of the nano particles on the moving components of an engine and the x-axis depicts the energy of the x-ray radiation used by the SEM. The energy of the x-ray radiation is represented in Kilo electron volts (Kev). In the graph 604, at peak 607 it may be noted that, the surface modified MoS₂nano particles result in deposition of Molybdenum (Mo) and sulphide (S) on the surface of the worn out balls thereby providing wear resistance.
Performance Test on Petrol Engine Test Rig
The performance test with lubricating oil is carried out on petrol engine by means of a specially designed test rig. The petrol engine test rig consists of an 800 cc 3 cylinder mpfi petrol engine of connected to an eddy current dynamometer. The morse test is generally used to determine brake power or power available at a crank shaft of the engine and various efficiencies of an engine. Morse test is carried out at different speeds and loads to determine various efficiencies of the engine with lubricants.
FIG. 7 illustrates graphical representations of variations in brake thermal efficiency of the MoS₂based nano suspension lubricant in a petrol engine test rig, according to an example implementation.
The graph 700 illustrated in FIG. 7 depicts the variation of brake thermal efficiency with brake power at 2500 RPM speed of the engine and the graph 702 illustrated in FIG. 7 depicts the variation of brake thermal efficiency with brake power at 4000 RPM speed of the engine. In the graphs 700 and 702 the y-axes depicts the brake thermal efficiency (η_{brake thermal}) and the x-axes depicts the brake power. The brake power is represented in watts.
From the graphs 700 and 702, an improvement in the brake thermal efficiency at lower as well as higher speeds of the engine is observed with the MoS₂based nano suspension lubricant. The MoS₂based nano suspension lubricant shows higher efficiency improvement at lower loads and lower speeds of the engine.
Performance Testing on Diesel Engine Test Rig
The performance test with a diesel engine oils carried out on Diesel engine test rig consisting of 1200 cc four cylinder, four stroke, Turbocharged CRDI diesel engine connected to an eddy current dynamometer for loading of the engine.
The specifications of the engine are as follows:


	Type	4 Cylinder, 4 stroke, CRDI engine
	Ignition	microprocessor based engine
		management system(ECU),
	Displacement	1250 cc
	Bore and stroke	Bore 69.6 mm, stroke 82 mm
	Maximum Power
	55 kW @ 4000 rpm
	Maximum Torque	190 Nm @ 2500 rpm
	Lubricant	SAE 15 W40 oil (factory recommended)

FIG. 8 graphically illustrates variations in brake thermal efficiency of the MoS₂based nano suspension lubricant in a diesel engine test rig, according to an example implementation. The graph 800 illustrated in FIG. 8 depicts the variation of brake thermal efficiency with brake power at 2500 RPM speed of the engine and the graph 802 illustrated in FIG. 8 depicts the variation of brake thermal efficiency with brake power at 4000 RPM speed of the engine. In the graphs 800 and 802 the y-axis depicts the brake thermal efficiency (ηbrake thermal) and the x-axis depicts the brake power. The brake power is represented in watts. It may be understood from the FIG. 8 that the MoS₂based nano suspension lubricant has enhanced brake thermal efficiency in the diesel engine test rig.
Endurance Test for Wear and Life of Engine with the MoS₂Based Nano Suspension Lubricant
The wear performance of lubricant is tested by subjecting the engine lubricated with the MoS₂based nano suspension lubricant to 80 hour test under cyclic loading on a test rig. The engine test rig consists of a 100 cc single cylinder petrol engine connected to an alternating current dynamometer.
The specifications of the engine are as follows:


	Type	Single Cylinder, 4 stroke, Twin spark
	Displacement
	100 cc
	Bore × stroke	50 mm × 49.5 mm
	Compression Ratio	8.8:1
	Maximum Power	7.8 bhp @ 7500 rpm
	Maximum Torque
	8 Nm @ 4500 rpm
	Ignition System	Digital Electronic Ignition
	Engine Start	Electric/Kick
	Maximum speed	7500 RPM

The alternating current dynamometer is used for loading the engine. The speed of dynamometer, voltage & current developed by dynamometer, fuel consumption and temperature of exhaust gases are measured. The cyclic loading is conducted with 16 cycles of 5 hrs cyclic loading. The cyclic loading of 2½ hour is done as per the sequence given in following table.

TABLE 2.9

Cyclic loading sequence for endurance test

	Test hours	Test Conditions

	2 hr	75% of full load at declared max speed
	2 hr	100% load at speed to maximum torque
	10 min	Idling
	50 min	100% load at declared max speed.

After the completion of the endurance test, the engine is dismantled and the conditions of the aforementioned design features, such as the cylinder liner of the engine and the piston rings are inspected for possible wear and tear. The wear of the cylinder liner is measured in terms of increase in diameter of the cylinder liner. The readings of diameter of the cylinder liner before & after the test are noted down and the difference is reported as wear loss of the cylinder liner. The wear losses of the cylinder liner for the MOS₂based nano suspension lubricant is given in the table below.
TABLE 2.10.1

Results of wear of the cylinder liner with the MOS₂based nano

suspension lubricant at different positions of the cylinder

Cylinder liner wear in μm

Position from petrol engine oil + 0.1%

TDC in cm petrol engine oil surface modified MoS ₂

2 5.0 4.5

4 6.5 4.75

4 7.5 4.75

8 7.55 3.0

Mean Wear in μm 6.64 4.25

Another parameter to be determined for determination of endurance of the engine is the wear of the piston rings in the engine. The wear of the piston rings are reported in terms of weight loss of the piston rings. The test results for weight loss of the piston rings are tabulated below.

TABLE 2.10.2

Results for weight loss of the
piston rings and gudgeon ring in 80 hr test

oil

		petrol engine oil + 0.1%
		surface modified
	petrol engine oil	MoS₂

Piston rings.	Serial	Weight loss mg	Weight loss mg

Compression ring

1	1IP	2	1
Compression ring 1	2IP	18	11
Expanding ring	E1		2	1
Oil ring 1	1SR	7	4
Oil ring 2	2SR	5	2

Total weight loss, mg	34	17
Gudgeon pin wear, mg	11	7

It may be noted from the Table 2.10.2 that the nano suspension lubricant having the MoS₂nano particles dispersed therein have substantially reduced the wear in the piston rings and the cylinder liners of the engine. Thus, the MoS₂based nano suspension lubricant offers better endurance to the engine.
Fuel Consumption Test
The fuel consumption is measured during the endurance test at an interval of 2 hours to assess the fuel efficiency of the nano suspension lubricant. The fuel consumption at an instant and total fuel consumption were recorded and tabulated in the table given below.

TABLE 2.11

Total fuel consumption rates during 80 Hr test

	Total fuel	Percentage
Lubricant used	consumed in litres	improvement

Lubricating fluid (petrol engine	93.300
oil)
Lubricating fluid + 0.1% surface	83.440	10.568
modified MoS₂nano particles

The results tabulated in the Table 2.11 is plotted in the graph 900 of FIG. 9. FIG. 9 graphically illustrates variation in total fuel consumption for the MoS₂based nano suspension lubricant, according to an example implementation. The y-axis of the graph 900 illustrated in FIG. 9 depicts the total fuel consumption and the x-axis depicts the time duration of the test. The time duration is expressed in hours and the total fuel consumption is expressed in Kg/hr. As may be observed from the graph 900 and the Table 2.11, the fuel consumption has reduced with the MoS₂based nano suspension lubricant as compared to the lubricating fluid without having nano particles. Based on the endurance test it may be concluded that the MoS₂based nano suspension lubricant exhibits a reduction in the wear of the components of the engine and improvement in the mileage of the engine. Further, based on the stability test, tribological tests, bench tests, and endurance tests, it may be concluded that for optimal results MoS₂nano particles from about 0.05 weight % to 0.1 weight % may mixed in the lubricating fluid.

Example 3

Tungsten Disulphide (WS₂) Based Nano Suspension Lubricant

According to an example implementation of the present subject matter, the nano suspension lubricant includes surface modified tungsten disulphide nano particles from about 0.05 weight % to 0.1 weight % dispersed in the lubricating fluid. The lubricant fluid includes about 90% to 99% base oil, such as, petroleum fractions, mineral oils, vegetable oils, synthetic oils, solvent refined mineral oils, hydrocracked mineral oils, polyalphaolefins, polyalkylglycols, synthetic esters, and the like. The lubricating fluid also includes about 1% to 10% additives, such as, antioxidants, detergents, and antiwear agents. The WS₂nano particles are coated with Cetrimonium Bromide (CTAB) surfactant to obtain surface modified WS₂nano particles. The surface modified WS₂nano particles from about 0.05 weight % to 0.1 weight % are dispersed in the lubricating fluid by stirring for about 1 hour in an ultra sound sonicator. The WS₂nano particles used have a size less that about 100 nanometers. In an example, SPAN 80 surfactant may be used for surface modification of the WS₂nano particles.
Stability Test for WS₂Based Nano Suspension Lubricant
Stability of the WS₂based nano suspension lubricant is evaluated using a Dynamic Light Scattering (DLS) technique. The DLS technique determines the size distribution profile of small particles in suspension or polymers in a mixture. The stability of any suspension is measured in terms of relative change in average particle size of the dispersed particles in the suspension. In a good suspension the size of the particles remain more or less same over a period of time.
The stability of the suspension in terms of average particle size is investigated over a period of 2 months. The variation of the WS₂nano particles surface modified with CTAB is shown in the following table.

TABLE 3.1

The average particle size of the surface modified WS₂nano particles
over a period of 60 days

		Average particle
		size of surface
		modified WS₂nano
		particles
	Day	expressed in nm.

	1^stDay	214.4
	15^thDay	244.3
	30^thDay	248.3
	60^thDay	255.32

As may be understood from the table 3.1, the average particle size of the surface modified WS₂nano particles over a period of 60 days did not have substantial change. This indicates good steric repulsions between the surface modified WS₂nano particles in the lubricating fluid and consequently better stability. Test results are illustrated below for the WS₂based nano suspension lubricant including lubricating fluids having different compositions for the base oil.
Tests for Physico-Chemical Properties
In an example implementation to analyze the physico-chemical properties of the WS₂based nano suspension lubricant, different tests such as Kinematic viscosity test, Total Acid Number test, Total Base Number test, and copper strip corrosion test are performed.
Kinematic Viscosity Test
Viscosity of the nano suspension lubricant is closely related to its ability to reduce friction. Viscosity index is a parameter that indicates the variation of viscosity with temperature. The Viscosity index is calculated as per ASTM D 445 standard by measuring viscosity of the WS₂based nano suspension lubricant at 40° C. and 100° C. A high value (normally >90) of the viscosity index indicates that the nano suspension lubricant has good lubricating properties.

TABLE 3.2

Viscosity index for the WS₂based nano suspension lubricant
with SM petrol engine oil (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Viscosity index

	Petrol engine oil SM grade	>110
	(SAE 20 W 40) + 0.05%
	surface modified WS₂nano
	particles
	Petrol engine oil SM grade	>110
	(SAE 20 W 40) + 0.1%
	surface modified WS₂nano
	particles

TABLE 3.3

Viscosity index for the WS2 based nano suspension lubricant with
diesel engine oil CI 4 grade (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Viscosity index

	Diesel engine oil CI 4 (SAE	>110
	15 W 40) + 0.05% surface
	modified WS₂nano particles
	Diesel engine oil CI 4 (SAE	>110
	15 W 40) + 0.1% surface
	modified WS₂nano particles

Total Acid Number Test
As explained above, maintaining a low TAN value is essential for lubricants to protect components of engines from acidic corrosion. Generally, a low TAN value (<3) gives an indication that the nano suspension lubricant is non-corrosive.
The table below illustrates the TAN values of the WS₂based nano suspension lubricant including surface modified WS₂nano particles dispersed in different lubricating fluids having different base oil compositions.

TABLE 3.4

Total Acid number with WS₂based nano suspension lubricant having
petrol engine oil SM grade (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Total Acid number

	Petrol engine oil SM grade (SAE 20	<2
	W 40)
	Petrol engine oil SM grade (SAE 20	<2
	W 40) + 0.05% surface modified
	WS₂nano particles
	Petrol engine oil SM grade (SAE 20	<2
	W 40) + 0.1 surface modified WS₂
	nano particles

TABLE 3.5

Total Acid number with WS₂based nano suspension lubricant having
diesel engine oil CI4 grade (SAE 15 W 40) as the lubricating fluid

	Lubricant used	Total Acid number

	Diesel engine oil CI4 grade (SAE 15	<2.2
	W 40)
	Diesel engine oil CI4 grade (SAE 15	<2.2
	W 40) + 0.05% surface modified WS₂
	nano particles
	Diesel engine oil CI4 grade (SAE 15	<2.2
	W 40) + 0.1% surface modified WS₂
	nano particles

Thus, as may be understood from the tables above, the Total Acid Number of the nano suspension lubricant dispersed with surface modified WS₂nano particles does not result in substantial change or deterioration of the total acid number of the nano suspension lubricant and is suitable for use in the automotive industry.
Total Base Number Test (TBN)
As explained earlier, the higher the TBN (typically >9), the more effective the nano suspension lubricant is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time. The tables below illustrate the TBN values of the WS₂based nano suspension lubricant including surface modified WS₂nano particles dispersed in different lubricating fluids having different base oil compositions.

TABLE 3.6

Total Base number with the WS₂based nano suspension
lubricant having diesel engine oil CI4 grade (SAE 15 W 40) as
the lubricating fluid

	Lubricant used	Total Base number

	Diesel engine oil	>10
	Diesel engine oil + 0.1% surface	>10
	modified WS₂nano particles with
	surfactant SPAN 80
	Diesel engine oil + 0.1% surface	>10
	modified WS₂nano particles with
	surfactant CTAB

TABLE 3.7

Total Base number with WS₂based nano suspension lubricant having
petrol engine oil SM grade (SAE 20 W 40) as the lubricating fluid

	Lubricant used	Total Base number

	Petrol engine oil	>6
	Petrol engine oil + 0.1% surface modified	>6
	WS₂nano particles with surfactant
	SPAN
80
	Petrol engine oil + 0.1% surface	>6
	modified WS₂nanoparticles with
	surfactant CTAB

Copper Strip Corrosion Test
The Copper Strip Corrosion Test is carried out to assess the relative degree of corrosiveness of a number of petroleum products, including aviation fuels, automotive gasoline, lubricating oils and other products. Hence, the copper strip corrosion test is performed for the WS₂based nano suspension lubricant.
In these tests, the petrol engine oil of SM 4 grade is selected as the lubricating oil. The lubricating oil mixed with surface modified WS₂nano particles was tested for copper strip corrosion test at 100° C. for 3 hours and the tarnish level of the copper strips were assessed against the ASTM Copper Strip Corrosion Standard. The results are shown in the table below.

TABLE 3.8

Copper strip corrosion test results for the WS₂based nano suspension
lubricant

Lubricant used	Copper strip corrosion result

Petrol engine oil of SM grade	1a
Petrol engine oil of SM grade + surface	1a
modified WS₂nano particles using CTAB
as surfactant
Petrol engine oil of SM grade + surface	1b
modified WS₂nano particles using SPAN
80 as surfactant

Thus, it may concluded that there is no abnormal deterioration of the physico-chemical properties of the WS₂based nano suspension lubricant. Further, it may be noted from the table 3.8 that CTAB is suitable as a surfactant for surface modification of the WS₂nano particles, at least for uses in the automotive industry.
Further, to assess the tribological properties, such as friction resistance, wear resistance, etc., of the nano suspension lubricant, wear and friction tests are performed on the WS₂based nano suspension lubricant. The wear and friction tests are conducted for the surface modified WS₂nano particles dispersed in different lubricating fluids at different load conditions.
The wear tests are conducted for each of petrol engine oil and diesel engine oil as the lubricating fluid at 40 kgf load and 60 kgf load. The wear tests on gear oils of GL 4 grade are conducted at 40 kgf and 80 kgf loads. Wear scar diameters (WSD) on the stationary balls are measured using a Metallurgical microscope.
FIGS. 10(a)-10(h) graphically illustrate the wear test results for the WS₂based nano suspension lubricant with the surface modified WS₂nano particle suspended in different lubricating fluids, according to an example implementation. In the graphs illustrated in the FIGS. 10(a)-10(h), the y-axis depicts the wear scar diameter and the x-axis depicts different compositions of the WS₂based nano suspension lubricant with different lubricating fluids, such as diesel engine oil, petrol engine oil, and gear oil. The wear scar diameter is represented in microns.
The graphs 1000(a)-1000(h) illustrate the wear test results for the WS₂based nano suspension lubricant. It may be concluded that based on the lubricating oil an optimum weight percentage of the nano particles may be chosen for best performance. As may be observed from the graphs, in general, the optimum weight % of the surface modified WS₂nano particles for best results lies between 0.05% to 0.1%.
Further, to determine the tribological properties of the WS₂based nano suspension lubricant friction test as per ASTM D 5183 standard have been performed. The friction tests have been conducted to determine the coefficient of friction of the WS₂based nano suspension lubricant under the following prescribed test conditions using ASTM 4 Ball wear test machine.


	Temperature	75 ± 2° C.
	Speed
	600 RPM
	Duration
	10 min at each load starting from 10 kgf
	Load	98.1 N (10 kgf) per 10 min increment to a load that
		indicate incipient seizure (sudden increase in friction
		force value over steady state) on the friction trace

FIGS. 11(a)-11(h) graphically illustrates the friction test results for the WS₂based nano suspension lubricant with the surface modified WS₂nano particle suspended in different lubricating fluids, according to an example implementation. It may be noted from the graphs 1100(a)-1100(h) that the WS₂based nano suspension lubricant has enhanced friction protection capabilities.
Further, to determine the wear characteristics of the WS₂based nano suspension lubricant, metallographic studies of worn out metallic balls used in the wear test can be performed. FIG. 12 graphically illustrates characterization of the worn out balls on scanning electron microscope with X-ray diffraction attachment for the WS₂based nano suspension lubricant, according to an example implementation. The graph 1202 depicts the deposition of tungsten and sulphur particles at peak 1203 on the worn out balls when the lubricating fluid, such as gear oil of GL 4 grade mixed with 0.05 weight % of the surface modified WS₂nano particles is being used for lubrication. The graph 1204 depicts the deposition of tungsten and sulphur particles at peak 1205 on the worn out balls when the lubricating fluid, such as gear oil GL 4 grade mixed with 0.10 weight % of the surface modified WS₂nano particles is being used for lubrication.
Performance Test on Petrol Engine Test Rig
The performance test with lubricating oil is carried out on the petrol engine test rig, as explained earlier. FIG. 13 graphically illustrates variations in brake thermal efficiency of the WS₂based nano suspension lubricant in a petrol engine rig, according to an example implementation. The graph 1300 illustrated in FIG. 13 depicts the variation of brake thermal efficiency with brake power at 2500 RPM speed of the engine and the graph 1302 illustrated in FIG. 13 illustrates the variation of brake thermal efficiency with brake power at 4000 RPM speed of the engine. In the graphs 1300 and 1302 the y-axes depicts the brake thermal efficiency (η_{brake thermal}) and the x-axes depicts the brake power. The brake power is represented in watts.
From the graphs 1300 and 1302, an improvement in the brake thermal efficiency at lower as well as higher speeds of the engine is observed with the WS₂based nano suspension lubricant. The WS₂based nano suspension lubricant shows higher efficiency improvement at higher loads and higher speeds of the engine.
Performance Testing on Diesel Engine Test Rig
The performance test of the WS₂based nano suspension lubricant with a diesel engine oil is carried out on the Diesel engine test rig, as explained earlier. FIG. 14 graphically illustrates variations in brake thermal efficiency of the WS₂based nano suspension lubricant in a diesel engine rig, according to an example implementation. The graph 1400 illustrated in FIG. 14 depicts the variation of brake thermal efficiency with brake power at 2500 RPM speed of the engine and the graph 1402 illustrated in FIG. 8 depicts the variation of brake thermal efficiency with brake power at 4000 RPM speed of the engine. In the graphs 1400 and 1402 the y-axis depicts the brake thermal efficiency (η_{brake thermal}) and the x-axis depicts the brake power. The brake power is represented in watts. From the graphs of FIG. 14 it is evident that the WS₂based nano suspension lubricant has an improved brake thermal efficiency.
Endurance Test for Wear and Life of Engine with the WS₂Based Nano Suspension Lubricant
The wear performance of the WS₂based nano suspension lubricant is tested by subjecting the engine lubricated with the WS₂based nano suspension lubricant to 80 hour test under cyclic loading on a test rig. The test conditions are same as for the endurance test performed in example 2 on the WS₂based nano suspension lubricant.

TABLE 3.9

Results of wear of the cylinder liner with the WS₂based nano
suspension lubricant at different positions of the cylinder

Cylinder liner wear in micrometer (μm)

		petrol engine oil + 0.1%
Position from		surface modified WS₂
TDC in cm	petrol engine oil	nano particles

2	5.0	4.00
4	6.5	3.50
4	7.5	3.00
8	7.55	4.50
Mean Wear in microns	6.64	3.75

Another parameter to be determined for determination of endurance of the engine is the wear of the piston rings in the engine. The wear of the piston rings are reported in terms of weight loss of the piston rings. the test results for weight loss in the piston rings are tabulated below.

TABLE 3.10

Results for weight loss of the
piston rings and gudgeon ring in 80 hr test

Components

		petrol engine oil +
		0.1% surface
		modified WS₂nano
	petrol engine oil	particles

Piston rings.	Serial	Weight loss mg	Weight loss mg

Compression

1IP

	2	1
ring 1
Compression	2IP	18	10
ring 1
Expanding ring	E1		2	2
Oil ring 1	1SR	7	3
Oil ring 2	2SR	5	1

Total weight loss, mg	34	19
Gudgeon pin wear, mg	11	5

It may be noted from the Table 3.10 that the nano suspension lubricant having the WS₂nano particles dispersed therein have substantially reduced the wear in the piston rings and the cylinder liners of the engine. Thus, the WS₂based nano suspension lubricant offers improved endurance to the engine.
Fuel Consumption Test
The fuel consumption is measured during the endurance test at an interval of 2 hours to assess the fuel efficiency of the nano suspension lubricant. The fuel consumption at an instant and total fuel consumption were recorded and tabulated in the table given below.

TABLE 3.11

Total fuel consumption rates for the WS₂based nano
suspension lubricant during the fuel consumption test

	Total fuel consumed in	Percentage
Lubricant used	litres	improvement

Lubricating fluid (petrol engine oil)	93.300
Lubricating fluid + 0.1% WS₂	82.970	11.072

The results tabulated in the Table 3.11 is plotted in the graph 1500 of FIG. 15. FIG. 15 graphically illustrates the variation in total fuel consumption for the WS₂based nano suspension lubricant, according to an example implementation. As may be observed from the graph 1500 and the Table 3.11, the fuel consumption has reduced with the WS₂based nano suspension lubricant as compared to the lubricating fluid without having nano particles. Thus, the WS₂based nano suspension lubricant provides improved mileage to automobiles.
Evaluation of EP Properties of the WS₂Based Nano Suspension Lubricant Using ASTM D 2783 Standard
The EP test determines the load carrying properties of the nano suspension lubricant. Generally, two parameters, such as Load-wear index and Weld load are evaluated to make this determination. Higher the value of the load wear index and weld load for a lubricant, the lubricant may be understood to have better EP properties.
The EP tests are carried out on the WS₂based nano suspension lubricant having gear oils of GL4 grade of viscosity grades of SAE 80 W 90 and EP 140 as the lubricant fluid. The results of the EP test are tabulated below:

TABLE 3.12

Variations in EP properties for the WS₂based nano
suspension lubricant with gear oil of GL 4 grade of viscosity
grade SAE 80 W 90 as the lubricating fluid

	load wear	weld
Lubricant used	index	load

Gear oil GL 4 (SAE 80W90)	55.17	250
Gear oil GL 4 (SAE 80W90) + 0.05%	60.94	315
WS₂surface modified with CTAB
Gear oil GL 4 (SAE 80W90) + 0.1%	60.32	315
WS₂surface modified with CTAB

FIGS. 16(a)-16(d) graphically illustrates the variation of extreme pressure (EP) properties of the WS₂based nano suspension lubricant, with the surface modified WS₂nano particle suspended in different lubricating fluids, according to an example implementation. The results of Table 3.12 are plotted in the graphs 1600(a) and 1600(b) illustrated in FIGS. 16(a) and 16(b), respectively. From the graphs of FIGS. 16(a)-16(d), it may be understood that the WS₂based nano suspension lubricant has improved EP properties.
Other embodiments of the present subject matter will be apparent from consideration of the present specification. It is intended that the present specification and examples be considered as illustrative only and as encompassing the equivalents thereof.

Claims

We claim:

1. A method for preparing a nano suspension lubricant, the method comprising:

providing substantially spherical nano particles of size ranging from about less than 50 nanometers to about 100 nanometers;

mixing the nano particles and a surfactant in about 1:1 ratio in a solvent to form a mixture;

evaporating the solvent from the mixture to obtain surface modified nano particles, wherein the surface modified nano particles include the nano particles coated with the surfactant; and

mixing the surface modified nano particles with a lubricating fluid to form the nano suspension lubricant, wherein the lubricating fluid comprises about 90% to 99% base oil and about 1% to 10% additives.

2. The method as claimed in claim 1, wherein the mixing the surface modified nano particles with the lubricating fluid includes sonicating the surface modified nano particles in the lubricating fluid in an ultra-sound sonicator at an amplitude of about 50% and a power of about 200 watts.

3. The method as claimed in claim 2, wherein the sonicating the surface modified nano particles in the lubricating fluid takes place for about 60 minutes, wherein the sonicating is performed in pulse mode with 0.5 second pulse for about 30 minutes and the sonicating is performed in continuous mode for remaining 30 minutes.

4. The method as claimed in claim 1, wherein the mixing the nano particles and the surfactant in the solvent includes stirring the nano particles and the surfactant in the solvent in an ultra-sound sonicator for about 7 to 8 hours.

5. The method as claimed in claim 1, wherein the evaporating the solvent from the mixture includes allowing the solvent to evaporate from the mixture at room temperature.

6. The method as claimed in claim 1, wherein the solvent is one of n-hexane, iso octane and toluene.

7. The method as claimed in claim 1, wherein the nano particles are selected from one of copper, molybdenum disulphide, and tungsten disulphide.

8. The method as claimed in claim 1, wherein the surfactant is selected from one of lauric acid, sorbitan monooleate, and cetrimonium bromide based on the electronegativity of the surfactant.

9. The method as claimed in claim 1, wherein the base oil is selected from one of petroleum fractions, mineral oils, crude oils, and a combination thereof.

10. The method as claimed in claim 1, wherein the additives in the lubricating fluid are selected from one of antioxidants, detergents, anti-foaming agents, anti-friction agents, anti-wear agents, and a combination thereof.

11. A nano suspension lubricant comprising:

a lubricating fluid comprising of about 90% to 99% base oil and about 1% to 10% additives; and

surface modified copper nano particles from about 0.05 weight % to 0.1 weight % dispersed in the lubricating fluid, wherein the surface modified copper nano particles include copper nano particles coated with lauric acid surfactant, wherein the copper nano particles have a size less than about 50 nanometers.

12. A nano suspension lubricant comprising:

surface modified molybdenum disulphide nano particles from about 0.05 weight % to 0.1 weight % dispersed in the lubricating fluid, wherein the surface modified molybdenum disulphide nano particles include molybdenum disulphide nano particles coated with Sorbitan Monooleate surfactant, wherein the molybdenum disulphide nano particles have a size less than about 100 nanometers.

13. A nano suspension lubricant comprising:

surface modified tungsten disulphide nano particles from about 0.05 weight % to 0.1 weight % dispersed in the lubricating fluid, wherein the surface modified tungsten disulphide nano particles include tungsten disulphide nano particles coated with Cetrimonium Bromide surfactant, wherein the tungsten disulphide nano particles have a size less than about 100 nanometers.