S. no.	Research article/authors	Material	Properties
1	Eswaraiah et al.34	Ultra-thin Graphene	(a) Graphene was prepared by solar exfoliation of graphite oxide, which removed almost 97% oxygen and made it hydrophobic (b) It can be added in a certain amount to improve base oil properties, including the coefficient of friction, load-bearing capacity, and the wear scar diameter (WSR) (c) When the concentration is around 0.025 mg/mL, load-bearing capacity increases while WSR and friction decrease (d) The absence of carboxyl and epoxide functional groups proved the hydrophobicity of graphene in FTIR spectra
2	Wu and Kao35	TiO2 nanofluid	(a) Gelation formed by using TiO2 in ethylene glycol (b) Friction force was reduced by using TiO2 nanoparticle in paraffin oil with conventional engine oil (c) Particle size has a direct relation with the coefficient of friction. 120 nm gave better results as compared to 220 nm
3	Liu et al.36	Carbon nanotubes (CNTs)	(a) The upgrading of thermal conductivity by adding CNTs into ethylene glycol and synthetic engine were studied (b) Thermal conductivity of CNT-ethylene glycol suspension enhanced by 12.4% up to volume fraction of 0.01 (c) Thermal conductivity of CNT-synthetic oil suspension enhanced by 30% up to volume fraction of 0.02 (d) The addition of CNTs into the base fluid formed a three-dimensional network that facilitates thermal transport (e) Fibers like CNTs were seen by the SEM and TEM images
4	Sidik et al.37		(a) Enhanced thermal conductivity and heat transfer was achieved by dispersing nanofluids in engine oil (b) The performance of the cooling system can be attained at a low volume fraction of nanoparticles (< 1%)
5	Zhang et al.38	Nano-graphite	(a) Nano-graphite was added to the heavy-duty diesel engine, and its performance was investigated (b) Around a 3% volume fraction of nano-graphite increased the cooling effect up to 15%
6	Mohammadi et al.39	γ-Al2O3, CuO	(a) γ-Al2O3 and CuO nanoparticles were used to enhance the thermal conductivity and heat capacity (b) Thermal conductivity was increased while heat capacity decreased when the concentration of nanoparticles increased (c) CuO increased the thermal conductivity by up to 8% while γ-Al2O3 just 5%
7	Vasheghani40	α-Al2O3, γ-Al2O3 & AlN	(a) Three types of Al nanoparticles were added in engine oil to enhance the thermal conductivity (b) Improvement of thermal conductivity by AlN was exceptionally better as compared to other components (c) The addition of 3% nanoparticles enhanced the property by 75.2% for AlN, followed by γ-Al2O3(20 nm) and α-Al2O3(20 nm) with 37.49% and 31.47% respectively
8	Ettefaghi et al.41	CuO	(a) Different concentrations of CuO nanoparticles (0.1, 0.3 & 0.5%) were added in engine oil to study its effect on thermal conductivity, flash, and pour point (b) Thermal conductivity and flash point increased by 3% and 7.5% by adding 0.1% volume fraction of CuO (c) The pour point has more value at 0.2% as compared to other concentrations
9	Wu et al.42	CuO, TiO2, nanodiamond	(a) Nanoparticles were added to the engine oil and base oil to study the tribological properties (b) The addition of CuO reduced the friction coefficients by 18.4% and 5.8% in engine and base oil, respectively (c) The sphere-like nanoparticles reduced the friction while the anti-wear mechanism was due to the deposition of nanoparticles on CuO worn surface
10	Ali et al.43	MoS2	(a) Heat transfer and lubrication properties were enhanced by adding MoS2 nanoparticles of different shapes (platelet, blade, cylindrical & bricks) (b) The heat transfer rate of blade-shaped nanoparticles enhanced by 7.87%, 9.64%, 14.33%, and 18.95% as compared to platelet, cylinder, and brick-shaped nanoparticles (c) Platelet shaped nanoparticles improved the convection heat transfer by 3.42%, 6.80%, 10.16% and 13.51%
11	Qiu44	Ni nanoparticles	(a) The load-carrying capacity was improved by the addition of Ni nanoparticles (b) Lower concentrations of Ni particles gave a better anti-wear performance, below 1% (c) The value of the friction coefficient is smaller when the concentration is between 0.2 and 0.5
12	Wong and Leon45	Al nanoparticles	(a) The addition of nanoparticles with diesel fuel increased the total combustion heat (b) The concentration of smoke and nitrous oxide decreased in the emission
13	Asadi and Pourfattah46	ZnO, MgO	(a) The viscosity and thermal conductivity have been studied over the temperature range (15–55 °C) and concentration (0.125–1.5%) (b) Thermal conductivity and viscosity showed an increasing trend as the temperature and concentration increased (c) The maximum enhancement was 28% and 32% for ZnO and MgO, respectively (d) The increase in dynamic viscosity took place at 55 °C and 1.5% by just over 124% and 75% for ZnO and MgO, respectively (e) None of these fluids are suitable for the laminar flow regime
14	Hu et al.47	Graphite nanoparticles	(a) Three critical properties were studied, including temperature, particle volume fraction, and the shear rate (b) Temperature behaved as an essential factor affecting viscosity as compared to volume fraction (c) The nanofluid behaved as a Newtonian (constant viscosity) if the shear rate is 17–68 s−1, but it gave non-linear behavior in the case of 667–3333 s−1
15	Soltani et al.48	WO3, MWCNTs	(a) The effects of volume fraction and temperature were studied on WO3/oil and MWCNT/oil (b) Volume fraction has a more significant effect on thermal conductivity than temperature, but both have a direct relation with conductivity (c) The maximum enhancement of thermal conductivity was at 60 °C and 0.6%
16	Esfe and Esfandeh49	ZnO-MWCNT	(a) MWNCT-ZnO (20–80%) has been added in 5W30 engine oil and their affect were studied on different VFs (0.05, 0.1, 0.25, 0.5, 0.75 and 1%) and temperatures (5–55 °C) (b) The mentioned nanofluid behaved as a non-Newtonian fluid, and the viscosity has decreased by increasing shear rate (c) The viscosity had a linear relationship with the VFs but non-linear with temperature
17	Liu et al.50	TiO2/Ag, Al2O3/Ag	(a) Both of these hybrid nanofluids behaved as shear-thinning fluid because viscosity decreases by increasing the shear rate (b) The viscosity and volume fraction sa linear relation with the hybrid nanofluids (c) The hybrid nanofluid containing the nanoparticles with different morphologies gave a low viscosity rate
18	Yesawani et al.51	Al2O3	(a) The addition of Al2O3 nanoparticles in 10W30 engine oil were studied based on viscosity and thermal conductivity (b) At higher concentrations, the viscosity has decreased (c) The reduction of thermal conductivity was different at different values of volume fractions and temperatures (d) The viscosity and thermal conductivity decreased by a maximum of 82.9% and 2.12% at 30 °C, 80.3%, and 3.5% at 60 °C, 80.5% and 5.12% at 80 °C respectively
19	Esfe et al.52	MWCNT-ZnO	(a) Addition of MWCNT-ZnO (1:4) to 5W50 engine oil and its lubrication properties were studied at different VFs (0.05, 0.1, 0.25, 0.5, 0.75, and 1%) and temperatures (5–55 °C) (b) The heat transfer rate was enhanced within 35–55 °C and at a VF less than 0.25%; it has a considerable effect on the performance of the car engine (c) The decrement of viscosity up to 9% achieved at a VF of 0.05% at 5 °C and shear rate of 666.5 s−1 (d) In hybrid nanofluid, the less dependency of viscosity on temperature proved better lubrication properties at higher temperatures
20	Yang et al.53	ZnO	(a) The stability of these nanoparticles was studied at various volume fractions and temperatures (b) The thermal conductivity increased with temperature and VFs (c) The maximum enhancement was obtained by 8.74% at VF and temperature of 1.5% at 55 °C respectively (d) The thermal performance of lubricant is better at high temperatures