Impact of Nano-Fuel Additives and Nano-Lubricant Oil Additives on Diesel Engine Performance and Emission Characteristics

1. Introduction

The decline in petroleum reserves and the growing need for energy supplies in recent years have been a subject of discussion among researchers. Diesel engines are essential in developing nations because they have a greater capacity for mileage and are more reliable and durable compared to petrol engines [ 1 , 2 ]. At present, diesel satisfies around 72% of the need for transportation fuel, while petrol accounts for 23%. The remaining demand is met by alternate fuels like CNG and LPG, which have been experiencing a consistent increase in demand. In 2016, Asia's total primary consumption accounted for 40% of the preceding decade, as reported by the U.S. Energy Information Administration (EIA) [ 3 ]. The significant increase in worldwide energy requirements indicates that reliance on oil supplies will continue to expand in the future. Furthermore, the excessive use of petroleum products is also intensifying the accumulation of hazardous contaminants in the environment [ 4 ].

Worldwide, air pollution is responsible for the deaths of three million people annually, according to World Health Organization research [ 5 ]. The research also demonstrated that the air quality index has been declining due to the rising number of vehicles on the road in recent years. Figure 1 shows some of the factors that are contributing to air pollution as a result of the increased number of vehicles on the road [ 3 ]. The research from the International Energy Agency (IEA) states that the only way to tackle the issues of undesirable climate change and our reliance on fossil fuels is for the world to move away from these fuels and towards alternatives [ 6 ].

Fig. 1. Factors affecting the quality of ambient air [3]

Various researchers performed experimental and numerical studies to identify different alternatives to fossil fuels, which involve various biofuels. The Global Biofuels Alliance was formed at the recently finished G20 meeting in New Delhi hosted by India. It is a project spearheaded by India and aims to bring together governments, international organizations, and businesses to encourage the use of biofuels [ 7 ]. The term "biofuel" refers to hydrocarbons that are made from organic materials using certain processes. The two most common types of biofuels are biodiesel and bioethanol.

Kumar et al. [ 8 ] performed an experimental study to investigate diesel engine performance by blending Jatropha methyl ester with tyre pyrolysis oil. They concluded that One of the environmentally favourable ways to generate energy is through the pyrolysis of used tyres. This method has additional benefits, such as producing energy and decreasing reliance on fossil fuels, which in turn lessens the strain of importing crude oil.

To forecast how diesel engines would operate when fed different types of biofuels, a variety of optimization techniques are used. Goga et al. [ 9 ] employ Artificial neural network (ANN) modelling to forecast the performance and emission parameters of a biogas-fueled compression ignition engine operating in dual fuel mode, as part of their investigation. With different engine operating loads and flow rates, ANN models are proven to be useful tools for predicting the performance and emission characteristics of biogas-operated dual-fuel diesel engines.

In order to improve combustion efficiency, fuel economy, and pollution reduction, numerous researchers have used 2D and 3D numerical simulations to analyze different engine modification strategies [ 10 ]. Modifications to engine designs and other methods for reducing diesel engine pollution were among the technologies documented by Rao and Sharma [ 11 ].

In comparison to engine modification techniques, fuel reformulation is easier, less expensive, and more widely used [ 12 ]. The combustion efficiency and fuel economy of CI engines are both enhanced by fuel reformulation, which also helps to reduce exhaust pollutants to a certain degree. Engine modifications, on the other hand, necessitate more expensive production and maintenance costs, as well as the replacement of vehicles powered by outdated diesel engines. The engine modification approach is less recommended because of the problems associated with it. Research efforts have largely focused on fuel modification strategies, which aim to make fuel in a way that is both sustainable and capable of ensuring fuel economy in the future [ 12 , 13 ].

Fuel additives show promise as a solution to the present problem. Blending additives with diesel, gasoline, or other alternative fuels improves the fuel's characteristics. Improving oxidation stability, deposit formation, corrosion resistance during long-term fuel storage, cold flow characteristics, and contamination are all areas where the additives shine. [ 14 , 15 ]. The fuel additives discussed can be categorised into various groups, including oxygenated additives, nanoparticles-based additives, water, tocopherol additives, and polymer-based additives. Table 1 provides a list of fuel additives along with their respective qualities.

The additives are blended in a minute proportion with the fuel, often ranging from 20 to 500 parts per million (ppm). Nevertheless, microscale additions encounter challenges such as sedimentation, aggregation, and non-uniform size distribution. Thanks to breakthroughs in Nano-sciences, it is now possible to easily create and utilize particles with diameters smaller than 100 nm as additives in the engine. This effectively resolves the aforementioned issues. The utilization of nanoparticles as additives in diesel and biodiesel fuels holds great potential for enhancing their effectiveness in the future [ 4 , 16 , 17 ].

The incorporation of nano-additives into fuels is accomplished using ultrasonication. Sonication utilizes high-frequency pressure sound waves to scatter the small particles within the base fluid. Figure 2 illustrates the sequential procedure of combining nanoparticles within the base fuel. However, the clustering of nanoparticles within the base fuel can frequently hinder the efficacy and stability of additives. Therefore, in order to resolve these problems, the solution is rendered stable through the utilization of surfactants and dispersants [ 18 , 19 ].

The primary role of the surfactant is to reduce the surface tension between liquids or between a liquid and a solid. The surfactants that are most suitable for blending additives with diesel and biodiesel are ethanol, isopropanol, span 80, and tween 80. Utilizing nanoparticles as an additive for both traditional and non-traditional/alternative fuels is the most promising method for significantly enhancing fuel performance [ 20 , 21 ].

Fig. 2. Nano-fuel preparation [3]

Nano-additives, which have dimensions in the nanometer range, possess a dense and elevated surface-to-volume ratio in comparison to traditional fluids [ 22 , 23 ]. Nanoparticles are categorized into five distinct categories based on their constituent elements, properties, and other characteristics, as depicted in Figure 3. The thermal conductivity of fluids is a significant factor in influencing the heat transfer capacity. Thermal conductivity plays a role in suspending tiny solid particles in fluids and modifying the fluid's transport characteristics, velocity, and heat transfer characteristics. The thermal conductivity of a base fluid can be improved by adding micrometre or millimetre-sized solid particles with a wide surface area and effective mixing capabilities [ 24 ].

Researchers conducted numerical and experimental investigations on the fluid flow and heat transfer properties of several nanofluids comprising SiO₂ [ 25 ], ZnO [ 26 ], CuO [ 27 ], Al₂O₃ [ 28 , 29 ], and Silver [ 30 ] nanoparticles. They evaluated characteristics such as viscosity, thermal conductivity, and the impacts of viscous dissipation. Raei [ 31 ] conducted a statistical study to analyse the heat transfer properties of Al₂O₃ – water nanofluid in a counter-flow heat exchanger using the Taguchi technique. He determined that the Nusselt number, which measures heat dissipation, may be enhanced by raising the concentration, flow rate, and temperature of the nanofluid.

Fig. 3. Classification of nanoparticles

Nanofluids exhibit superior stability in comparison to traditional fluids, owing to the size-dependent phenomenon and the random motion of the nanoparticles known as Brownian motion. The nanoparticles' ultrafine form enables unrestricted fluid flow in a microchannel, promoting smoothness. In addition, the utilization of nanofluids allows for a reduction in the size of the heat transfer system, resulting in improved heat transfer performance [ 32 ]. Here, the calorific value (CV) of fuel can be enhanced by the increased energy density of the nanoparticles, resulting in greater engine performance.

The nanoparticles function as a catalyst in the combustion process and exert a beneficial influence on ignition parameters. The particles enhance the momentum density, hence increasing the velocity of fuel injection into the combustion chamber and resulting in improved engine performance [ 22 ]. The distinctive physicochemical properties, such as magnetic, optical, and electrical features, of nanoparticles have led to their extensive use as fuel catalysts. These catalysts effectively minimize ignition delay, specific fuel consumption (SFC), hazardous emissions, and smoke while also enhancing the brake thermal efficiency (BTE) of the engine.[ 17 ]. The incorporation of nano-powdered metal and metal oxide into the base fuel can improve the characteristics of the fuels [ 33 ].

Several researchers have utilized nanoparticles as additives in both diesel and biodiesel to create novel hybrid fuel blends. In their study, Ganesh et al. [ 34 ] conducted an experimental analysis to examine the performance characteristics of a diesel engine with a single cylinder. The engine was fueled with Jatropha biodiesel and included the use of magnalium and cobalt oxide nanofuel additives. Due to the reduced calorific value of Jatropha biodiesel, there was a drop in brake thermal efficiency (BTE) and an increase in brake-specific fuel consumption (BSFC). Nevertheless, the inclusion of magnesium and cobalt oxide nanoparticles increases the brake thermal efficiency of the engine by approximately 1% when compared to biodiesel without any additions.

Hosseini et al. [ 35 ] investigated the impact of carbon nanotubes as fuel additives on the performance of an engine and the characteristics of its emissions. The engine used in the study was a single-cylinder CI engine. It was noticed that the inclusion of carbon nanotubes reduces engine emissions, specifically unburnt hydrocarbons (UHCs), carbon monoxide, and soot. Furthermore, the engine's performance, such as brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC), was much improved. Hoseini et al. [ 36 ] conducted a study where they investigated the use of graphene oxide (GO) nanoparticles as additives in a combination of biodiesel and diesel fuel. The blend was tested on a single-cylinder diesel engine. By employing GO nanoparticles, a decrease of approximately 5% to 22% in Carbon monoxide and a reduction of about 17% to 26% in UHCs were found. Nevertheless, under the same circumstances, there was an observed increase of approximately 7% to 11% in CO₂ emissions and a rise of roughly 4% to 9% in NOx emissions.

Ghanbari et al. [ 37 ] conducted an experimental study on a six-cylinder diesel engine to examine its performance and emissions when using nano-silver particles (at concentrations of 40, 80, and 120 ppm) and multiwall carbon nanotubes (at concentrations of 40, 80, and 120 ppm) as additives to the diesel fuel. The inclusion of these compounds resulted in a decrease of around 7.08% in brake-specific fuel consumption (BSFC). Furthermore, there was a reported increase of around 2% in engine torque and power when compared to diesel fuel. The researchers noted a significant decrease in the release of unburned hydrocarbon (UHC) and carbon monoxide (CO) when using carbon nanotubes.

Gumus et al. [ 38 ] conducted an experimental study on a six-cylinder, direct ignition air-cooled CI engine to investigate the performance characteristics and emission qualities. The engine was fueled with a diesel fuel additive containing silver nanoparticles. By introducing 10 ppm and 20 ppm of silver nanoparticles, the brake-specific fuel consumption (BSFC) decreases by approximately 2% in comparison to regular diesel fuel.

Mehta et al. [ 39 ] assessed the efficiency of a diesel engine by including aluminium (Al), iron (Fe), and boron (B) nanoparticles as additives to the diesel fuel. The results showed a decrease of around 7% in Brake Specific Fuel Consumption (BSFC) as compared to diesel fuel without any additives. Kannan et al. [ 40 ] conducted an experimental study on a direct-injection diesel engine. They investigated the engine's performance, emissions, and combustion characteristics when fueled with palm biodiesel. In their study, they used ferric chloride (FeCl3) as a fuel-borne catalyst (FBC). It was noted that the addition of FeCl3 resulted in a 6.3% increase in Brake Thermal Efficiency (BTE), while the Brake Specific Fuel Consumption (BSFC) decreased by 8.6%. In addition, a small rise in CO₂ emissions resulted in significant decreases in carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC), and smoke emissions.

Ağbulut [ 41 ] examines the impact of nanoparticle size on the performance of a CI engine from both a thermodynamic and economic perspective. The results indicate that the particle size of nanomaterials significantly impacts the performance of internal combustion engines. Smaller particle sizes of nanoparticles of the same type should be prioritized for improved energy, exergy, thermo-economic, exergo-economic, and sustainability outcomes.

Ağbulut et al. [ 42 ] investigates the impact of directly adding a high dose of copper oxide (CuO) nanoparticles (<77 nm) to conventional diesel fuel in their further study. Decreases of 14.6% and 20.8% in CO emissions, 6.2% and 13.4% in HC emissions, and 4% and 4.7% in NOx emissions were observed with CuO additions of 1000 and 2000 ppm, respectively. In addition, Ağbulut et al. [ 43 ] propose that including metal-oxide based nanoparticles in biodiesel blends yields superior outcomes compared to utilizing biodiesel alone in CI engines.

An investigation into the development and use of surfactant-modified catalytic ceria nanoparticles as fuel additives in a 4-stroke diesel engine powered by biodiesel derived from coconut oil is detailed in the work of Roy et al. [ 44 ]. Here, efficiency improved by 5% during the load test, with a 45% drop in hydrocarbon (HC) emissions and a 30% drop in nitrogen oxide (NOx) emissions at higher loads.

A single-cylinder, four-stroke, naturally aspirated compression ignition (CI) diesel engine was the subject of extensive exergetic and exergo-economic calculations carried out by Karagoz et al. [ 45 ]. In their investigation, the test engine was run on a variety of fuels, including diesel, a blend of 90% diesel and 10% waste cooking oil (D90B10), D90B10 with 100 ppm of Al₂O₃ nanoparticles, D90B10 with 100 ppm of TiO₂ nanoparticles, and D90B10 with 100 ppm of SiO₂ nanoparticles. According to the results of the exergy, exergo-economic, and sustainability analyses, Nano fuel outperformed neat diesel fuel and diesel-biodiesel blend. When considering all the analyses, it is concluded that the best test fuel for this study is Nano fuel doped with Al₂O₃.

The study conducted by Siddartha et al. [ 46 ] aims to examine the impact of various additives on the performance, combustion, and emission characteristics of diesel engines when used in biodiesel. The researchers determine that the utilization of diverse fuel additives in conjunction with biodiesel aids in diminishing numerous detrimental emissions, hence facilitating the attainment of a sustainable environment and mitigating the unfavorable consequences of global warming, such as climate change.

Hoang et al. [ 47 ] present an exhaustive literature review to demonstrate the performance of CI engines with diesel and biodiesel as base fuel and metal nanoparticles as fuel additives. Table 2 provides a summary of the comparison results on how nanoparticles affect the performance and emission characteristics of a compression ignition (CI) engine operating under different situations. In summary, choosing a suitable nano-additive is a highly effective method to improve the characteristics of various alternative fuels and mitigate the negative emissions associated with CI engines.

In CI engines, to decrease consumption of energy and hence lower CO₂ emissions, it is imperative to enhance the energy efficiency of mechanical systems. A significant approach to do this is by developing lubricants that minimize friction in machine components. An effective design strategy involves optimizing the rheology of the liquid lubricant to minimize hydrodynamic shear, churning, and pumping losses. Practically, this typically involves decreasing the thickness of the lubricant to the minimum level that still allows for the presence of fluid or mixed film lubrication.

An alternative method involves incorporating minute amounts of friction modifier additives into the lubricant to decrease friction in the boundary and mixed lubrication conditions. Figure 4 presents a summary of the progress in the development of lubricating additives, as documented by Spikes [ 48 ]. The scientific study of friction, lubrication, and wear is referred to as Tribology. The method employed to decrease wear and friction is the field of Tribology. The occurrence of machine failure can be attributed to friction and wear, resulting in the wastage of significant energy owing to friction in machine components.

Fig. 4. Timeline summary of development of lubricating additives [48]

To address these problems, the most efficient strategy is to apply lubrication to the machinery. Lubricants are extensively employed in various industries and production facilities to safeguard items and instruments against deterioration and uphold their respective surface structure. In addition, lubricants enhance the coefficient of friction (COF) of manufacturing processes and reduce the buildup of surplus heat in mechanical systems.

Therefore, it is crucial to prioritize the improvement of lubricating oil qualities in order to safeguard machinery from potential problems and reduce energy usage [ 64 ]. Base fluids in diesel engines have the vital function of lubricating and creating a barrier between moving surfaces, as well as removing heat, preventing wear, and preventing contamination in the system.

Nevertheless, it is necessary to incorporate appropriate additives into any lubricating oil mixture to improve specific characteristics, such as resistance to oxidation, reduction of friction and wear, protection against corrosion, and stability against biological breakdown.

Another concern is that the base fluid, which acts as a carrier for additives, must have the ability to retain the additives in the solutions under all working circumstances [ 65 ]. Approximately 10% of the weight of the final lubricant product consists of additive packages.

Nevertheless, this can vary considerably, depending on the uses [ 66 ]. According to Rudnick [ 67 ], the lubricant additives can be classified as illustrated in Figure 5.

Fig. 5. Classification of general lubricant additives utilised in industry [67]

In recent years, there has been a major rise in research on lubricants that incorporate nanoparticles to effectively manage systemic wear and friction. A broad spectrum of research has been conducted on organic and inorganic nanoparticles for their utilization as extreme pressure (EP) and anti-wear agents. Friction researchers explored many perspectives on the adsorption, penetration, and tribo-chemical reaction related to the friction-reducing properties and anti-wear processes of nanoparticles. Research has demonstrated that nanoparticle additives have superior tribological capabilities compared to conventional solid lubricant additives .Studies on nanoparticle additives are categorized into metals, metal oxides, non-metals, nano carbon-materials, and Boron-based nanoparticles. Ali et al. [ 73 ], Waqas et al. [ 74 ], Shahnazar et al. [ 75 ] and Srivyas and Charoo [ 76 ] were presented an exhaustive review on application of nanoparticle additives in lubricants to improve its tribological properties. Table 3 shows several earlier research works carried out on metal oxide nanoparticles as lubricant additives.

Based on the literature study, it is evident that the majority of researchers investigate the performance of CI engines by incorporating nanoparticle additives into either the base fuel or the lubricants. There is a scarcity of information that investigates the impact of adding nanoparticles to both the base fuel and lubricant. The author is motivated to conduct a study to investigate the performance of CI engines and their emissions by including nanoparticle additions in either the basic fuel or lubricants.

The primary objectives of the present experimental study are as follows:

• 1. To analyze the performance of a diesel engine by introducing nanoparticle additions into either the basic fuel or the lubricants. In this case, a combination of CuO and ZnO nanoparticles is used as additives for diesel fuel. The lubricating oil additives consist of a combination of Al₂O₃ and ZnO nanoparticles.
• 2. To assess the performance of the diesel engine by analyzing several engine parameters such as Specific Fuel Consumption (SFC), Brake Thermal Efficiency (BTE), Mechanical Efficiency (ME), Volumetric Efficiency (VE), Noise level, and changes in lubricating oil viscosity.
• 3. To evaluate the emission performance of a diesel engine by analyzing the exhaust gases for parameters such as smoke density, NOx emission, CO and CO₂ emissions, and Hydrocarbon (HC) emission.

2. Materials and Methods

2.1. Preparation of Nanofuel and Nano Lubricating Oil

The current study used regular diesel as the primary fuel for the compression ignition engine. According to the engine handbook provided by Kirloskar Oil Engines Limited [ 83 ], it is recommended to use SAE 15W-40 engine oil as a lubricant for diesel engines. Additionally, the SAE 15W-40 lubricant is appropriate for use in vehicle diesel engines, particularly those with inter-cooling and turbocharging. The SAE 15W-40 lubricant oil offers wear protection to engine components and effectively minimizes the accumulation of abrasive deposits [ 84 ].

For the current study, nanoparticles are mixed with base fuel and lubricant oil by sonication process by sonicator equipment available at Ankleshwar Research and Analytical Laboratory (ARAIL), Ankleshwar, Gujarat, India. The steps involved in the preparation of nano fuel are depicted in Figure 6. Nanoparticles of different materials are purchased from M/s. Adnano Technologies, Karnataka, India. Table 4 shows various properties of nanoparticles.

Fig. 6. Steps involved in nano fuel preparation [42]

Every individual nanoparticle is measured to have a mass fraction of 100 parts per million (ppm). Specifically, a 100mg nanoparticle was added to 1kg of diesel fuel. The suspended nanoparticles mass was measured using Radwag brand precision scales (Model: AS 110.R2 PLUS Analytical Balance) with an accuracy of ± 0.001g. Subsequently, the nano-fuel blend was evenly distributed using a Bandelin Sonorex brand ultrasonic bath (Model: Digitech DT 514 H) [ 85 ], operating at a frequency of 35kHz and a power of 320W for a duration of one hour.

A nano fuel blend consisting of diesel fuel mixed with copper oxide (CuO) and zinc oxide (ZnO) nanoparticles was created. The quantity of the blend was 7 liters, as shown in Figure 7 (a).

The same procedure was utilised to create a mixture of SAE 15W-40 engine oil with nanoparticles of aluminum oxide (Al₂O₃) and zinc oxide (ZnO) to produce lubricant blends. The volume of the mixture was 5 liters, as indicated in Figure 7 (b).

Fig. 7. (b). SAE 15W-40 lubricant engine oil and lubricant blends

The test fuels possessed the main characteristics outlined in Table 5.

2.2. Experimental Setup

Table 6 displays the comprehensive parameters of a two-cylinder vertical, four-stroke, single-acting, high-speed, water-cooled compression ignition engine. The centrifugal governor controlled the velocity of the engine.

The engine was linked to a computerized electrical dynamometer in order to quantify the power generated. The engine was equipped with instruments to measure parameters such as fuel consumption, engine load and speed, cooling water temperature, inlet air temperature, exhaust gas temperature, and smoke density. The experimental setup is depicted schematically and pictorially in Figures 8 and 9. The engine was tested from no load to maximum load circumstances while maintaining a constant speed of 1500 rpm and varying the load. The measurements of several parameters were documented at every stage of the operation.

Fig. 8. Schematic diagram of the experimental set up

The following cases were tested in an experimental setup: (1) a base engine with pure conventional diesel and SAE 15W-40 engine lubricant oil; (2) a modified nano lubricant oil and pure conventional diesel; and (3) a modified nano fuel and modified nano lubricant oil.

Fig. 9. Pictorial diagram of the experimental set up

At each operating point, the engine's specific fuel consumption, brake thermal efficiency, mechanical efficiency, volumetric efficiency, noise level, lubricant viscosity, and exhaust gases were measured. It was also necessary to wait for the engine to stabilize before recording the dynamometer load, speed, fuel, and air flow under each running condition. Table 7 displays the associated uncertainty in the computed characteristics with regard to the measured parameter.

3. Results and Discussion

3.1. Specific Fuel Consumption (SFC)

Specific fuel consumption is a criterion used to assess the performance of engines of different sizes. This is the correlation between the rate of fuel consumption and the amount of energy produced by the engine. High fuel consumption in the engine indicates a greater need for fuel to generate power, resulting in less efficiency. Figure 10 illustrates the relationship between specific fuel consumption (SFC) and changes in brake power. It has been noted that the specific fuel consumption (SFC) reduces to its lowest value as the brake power increases up to the optimal loading state and then slightly increases in overload situations.

Case-2 demonstrates a decrease in fuel consumption while utilizing a modified nano lubrication oil in combination with pure diesel base fuel, while Case-3 exhibits an even greater reduction in fuel consumption by utilizing a modified nano fuel with the modified nano lubricant oil. This performance behavior is attributed to the reduction of heat loss and the achievement of total combustion in the chamber.

Fig. 10. Variation in SFC with respect to Brake power

Under optimum load conditions, the specific fuel consumption for Case-3 is around 248 g/kW-hr. Case-3 shows a decrease in SFC of approximately 14.98% compared to Case-1, and a decrease of approximately 11.91% compared to Case-2.

3.2. Brake Thermal Efficiency (%)

The brake power and calorific value of fuel are utilized to determine brake thermal efficiency (BTE). The inverse of specific fuel consumption is Brake thermal efficiency. Figure 11 demonstrates that the BTE (Brake Thermal Efficiency) of all the fuels examined is inferior to that of diesel fuel. The brake's thermal performance improves as the loads grow.

Fig. 11. Variation in BTE with respect to engine torque.

Figure 11 demonstrates that Case-2 and Case-3 display an improved Brake Thermal Efficiency (BTE) in comparison to Case-1, which represents the standard engine without nano additions. The utilization of nano-lubricants (Al₂O₃+ZnO) in SAE 15W-40 engine lubricant oil with diesel enhances brake thermal efficiency. This efficiency is further elevated by the combined use of both nano-fuel and nano lubricant oil.

Under the rated power conditions, the brake thermal efficiency for Case-1 is 29.33%. Based on the data, it can be noticed that Case-3 shows the biggest improvement in BTE, with an enhancement of approximately 34.50%. In comparison, Case-2 exhibits an increase in BTE of up to 30.39%. The increase in thermal braking efficiency of the diesel mixture can be attributed to its higher energy content and calorific value in comparison to diesel. As a consequence, this leads to increased breakdown, thorough combustion, and elevated heat generation.

3.3. Mechanical Efficiency (%)

Based on the data presented in Figure 12, it can be noticed that the mechanical efficiency (ME) improves as the load condition, specifically engine torque, increases. The highest mechanical efficiency is obtained in Case-3. It has been observed that the mechanical efficiency (ME) of Case-2 and Case-3 is consistently higher than that of Case-1, which is the base engine, for all levels of engine torque. The improvement in lubricant oil characteristics is due to the inclusion of nanoparticles (Al₂O₃+ZnO) as a lubricant additive. Additionally, this reduces the frictional power of the diesel engine.

Fig. 12. Variation in ME with respect to engine torque.

The mechanical efficiency of the Case-1, the standard engine without nano additions, is 63.98% at optimal load conditions. The addition of nano compounds can increase mechanical efficiency to 66.38% for Case 3 and 66.50% for Case 2.

3.4. Volumetric Efficiency (%)

The base engine (Case-1) achieves a maximum volumetric efficiency (VE) of 82.92% under the rated condition. The incorporation of nano additives in fuel and lubricants, along with the achievement of complete combustion in the chamber, leads to a decrease in volumetric efficiency. Specifically, in Case-2, the reduction is 1.40%, while in Case-3, it is 3.18%, as compared to Case-1. This information is visually shown in Figure 13. In this case, the full combustion process shows an increase in both peak pressure and exhaust pressure, leading to a decrease in the amount of air taken in. Therefore, a significant decrease in VE is noticed during the process.

Fig. 13. Variation in VE with respect to engine torque.

3.5. Noise Level

The noise level for the base engine (Case-1) was measured to be between 91.7 dB and 93.5 dB under optimal load conditions. According to Figure 14, the addition of nano-lubricant additives and nano-fuel additives leads to an increase in noise level.

By incorporating nanoparticles into the base fuel and lubricating oil, it has been noticed that the noise levels for all the different scenarios are consistently below the acceptable threshold, even under normal operating conditions.

3.6. Variation in Lubricant Oil Viscosity

The properties of oil viscosity and residue in SAE 15W-40 engine lubricant oil and modified nano lubricants (containing Al₂O₃ and ZnO nano particles) were analyzed at Ankleshwar Research & Analytical Laboratory (ARAIL) in Ankleshwar, Bharuch, India. This analysis was conducted using a Capillary U-Tube Viscometer according to ASTM D446 standards [ 86 ].

Fig. 14. Noise level at rated torque conditions

Figure 15(a) demonstrates that the viscosity of SAE 15W-40 engine lubricant oil at 40°C and 100°C is lower when compared to the viscosity of modified nano-lubricant oil obtained by blending base engine oil with nanoparticle additives. Higher viscosity indicates a lubricant oil that is stable and aids in the formation of a reliable lubricating layer between engine components, especially at varying temperatures. The presence of a nanoparticle between the oil layers facilitates smooth and effortless motion between the nano-lubricant oil, reducing the amount of viscous friction.

Furthermore, Figure 15(b) illustrates the viscosity index of both SAE 15W-40 engine lubricant oil and modified nano-lubricant oil. The viscosity index of the modified nano-lubricant oil is found to be 0.484% more than that of the SAE 15W-40 engine lubricant oil. The addition of Al₂O₃ and ZnO nanoparticles to SAE 15W-40 engine lubricant oil results in an increase in the viscosity index. This increase signifies a more consistent viscosity when subjected to changes in temperature. Nevertheless, it has been noted that an increase in resistance to thinning of the lubricating oil layer leads to improved fuel economy.

Fig. 15. Variation viscosity of lubricating oil

3.7. Heat Balance Sheet

A heat balance sheet is created for a twin-cylinder 4-stroke diesel engine to account for the heat supplied by fuel (HS), the heat equivalent to brake power (H. BP), the heat carried by cooling water jackets (H. CW), the heat carried by exhaust gas (H. EX), and the heat lost by radiation and unaccounted losses (H. UC).

Figure 16 shows that the base engine for Case-1 uses 29.42% of its heat for brake power. This rises to 30.39% for Case-2 when nano-lubricant is added, and it goes up to 34.50% for Case-3 when nano-fuel is added as well.

Fig. 16. Heat balance sheet

Figure 16 demonstrates that the amount of heat used to pr`oduce brake power (H. BP) goes up when the amount of heat lost in jacket cooling water (H. CW) and exhaust gases (H. Ex) goes down. The amount of heat unaccounted (H. UC) is also lowered from 37.5% to 35.48%.

3.8. Exhaust Gas Analysis

3.8.1. Smoke Density

Figure 16 shows how the density of the smoke changes when the engine power is changed in terms of engine torque. One way to measure the amount of smoke released is by its opacity. A diesel car releases a lot of smoke. Poor repair or motors that don't work right can sometimes make smoke worse. The test findings are contingent upon the level of obscurity and the age of the diesel engine.

Figure 17 shows that the smoke density of Case-2 decreased by 4.44%, and Case-3 decreased by 20% compared to Case-1 of the diesel engine without any nano additives. The decrease in smoke density indicates that the inclusion of nano-fuel additives and nano-lubricant additives promotes a more thorough combustion process.

Fig. 17. Variation in smoke density with respect to engine torque

Furthermore, it has been noted that when the engine torque increases, there is a significant increase in smoke density. This phenomenon can be attributed to the overall abundance of fuel in the air mixture. The amount of smoke produced is influenced by factors such as temperature, duration of the diffusion combustion phase, and reduced oxygen levels. This could be attributed to the process of fuel atomization and the resulting incomplete combustion.

3.8.2. NOx Emission

Figure 18 illustrates the variation in NOx emissions as the engine power is adjusted in relation to engine torque. Nitrogen dioxide and nitric oxide are often referred to as nitrogen oxides (NOx). Nitrogen oxides are gaseous compounds that undergo chemical reactions to produce smoke and acid rain. They also play a crucial role in the creation of particulate matter (PM) and ground-level ozone, both of which are linked to negative health impacts. NOx emissions are increased by an excessive load on CI engine.

Fig. 18. Variation in NOx emission with respect to engine torque

According to Figure 16, Case-2 and Case-3 show a decrease of approximately 1.46% and 10.25% in NOx emissions compared to Case-1 of the diesel engine without any nano additions, respectively. This result is attributed to the chemical reaction between diesel fuel and CuO nanoparticles mixed with the base fuel as nano-fuel additives.

3.8.3. CO Emission

Carbon monoxide (CO) is a combustible gas. It has no color, smell, or taste, and it is slightly more dense than air. Increase in engine loads will raise the CO emissions. If combustion is incomplete, it may cause more emission pollution. If burning isn't finished, it may cause more pollution. This might be because the pre-mixture didn't burn quickly and the diesel mixture had a high viscosity, which caused the droplet volume to rise and the mixture to not dissolve well.

Figure 19 illustrates the relationship between carbon monoxide (CO) emission and engine torque. The incorporation of ZnO as nano additives in modified nano-fuel enhances the engine combustion process. Consequently, there is a noticeable decrease in CO emissions. Case-2 shows a reduction of 4.96% in CO emissions compared to Case-1, while Case-3 demonstrates a reduction of 20.04%.

Fig. 19. Variation in CO emission with respect to engine torque

3.8.4. CO2 Emission

Carbon dioxide is a chemical molecular structure composed of a single carbon atom and two oxygen atoms. Carbon dioxide (CO₂) exists in small amounts in the Earth's atmosphere and functions as a greenhouse gas. In a solid state, it is referred to as dry ice. It plays a crucial role in the carbon cycle.

Here, Figure 20 illustrates the relationship between carbon dioxide (CO₂) emission and engine torque. It is observed that the emission of CO₂ is increased in the exhaust gas by using both modified nano-fuel and nano-lubricant additives with diesel. The highest increase of 29.16% is recorded in Case-3 compared to Case-1, which did not involve any nano additions. Furthermore, there is an observed rise of approximately 4% in Case-2 compared to Case-1.

Fig. 20. Variation in CO₂ emission with respect to engine torque

3.8.5. Hydrocarbon (HC) Emission

Figure 21 illustrates the correlation between the emission of hydrocarbons (HC) and the torque produced by the engine. A hydrocarbon is a kind of organic substance composed of atoms of hydrogen and carbon. Hydrocarbons are organic chemicals that serve as the fundamental components of crude oil, natural gas, coal, and other significant sources of energy.

The levels of hydrocarbon rise as development advances. The elevated levels of hydrocarbons (HC) might be attributed to inadequate dissolving of the diesel mixture, which can be attributed to its high viscosity, high density, and low volatility.

Fig. 21. Variation in HC emission with respect to engine torque

Figure 21 demonstrates that the addition of nano-fuel additives and nano-lubricant additives leads to a significant decrease in hydrocarbon emissions in exhaust gas, indicating a complete combustion process.

It is observed that Case-2 shows a reduction of 1.15% in HC emissions compared to Case-1, whereas Case-3 demonstrates a larger reduction of 7.17%.

4. Conclusions

From the current experimental work, it is concluded that thermal efficiency can be enhanced by adding CuO and ZnO nanoparticles in fuel (conventional diesel) as nano-fuel additives and Al₂O₃ and ZnO nanoparticles in engine lubricant (SAE 15W-40 engine lubricant oil) as nano-lubricant additives, respectively. Reduction in NOx, CO, unburnt HC and Smoke density in the exhaust are observed, whereas CO₂ emission increases, which clearly indicates complete combustion in diesel engines.

The engine performance is compared for three different cases – (1) a base engine with pure conventional diesel and SAE 15W-40 engine lubricant oil; (2) a modified nano lubricant oil and pure conventional diesel; and (3) a modified nano fuel and modified nano lubricant oil. After analyzing the experimental outcomes, it can be concluded that:

• 1. A reduction of about 11.91% in specific fuel consumption (SFC) is shown when only modified nano lubricants are utilized (in Case-2), compared to Case-1 where no nano additives are utilized. Whereas about 14.98% reduction is noted with the addition of nanoparticles in both fuel and lubricants in Case-3 as compared to Case-1. Here, application of nanoparticles as additives in both fuel and lubricant can significantly reduce the specific fuel consumption. The addition of nano-fuel additives and nano-lubricant additives to diesel fuel and lubricant oil, respectively, increases the brake thermal efficiency by 17.62% in Case-3. In comparison, the blend of pure diesel and lubricant oil with nano-lubricant additives in Case-2 increases the efficiency by 3.61% compared to the basic engine without additives.
• 2. The mechanical efficiency of diesel engine is raised by an average of approximately 3.94% in both modified cases.
• 3. The viscosity index of the modified nano-lubricant oil is around 0.484% higher compared to the basic SAE 15W-40 engine lubricant oil. This implies that the viscosity property of the blend remains more stable as the temperature increases.
• 4. The noise level for all load conditions is well within the permissible limit.
• 5. The addition of nano-fuel additives to diesel fuel and nano-lubricating additives to lubricant oil enhanced combustion by reducing the density of smoke, as well as the emissions of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). The addition of nano-fuels and nano-lubricants to the basic fuel results in an increase in CO₂ emissions in exhaust gases, indicating that the combustion process is moving towards complete combustion. By incorporating fuel and lubricant additives into diesel engines, it is possible to enhance engine performance by reducing fuel consumption and minimizing exhaust gas emissions.

Acknowledgments

The authors would like to acknowledge Mr. Kaushal S. Shah, PG Scholar, Department of Mechanical Engineering, Shri S’ad Vidya Mandal Institute of Technology, Bharuch, Gujarat, India for his support in taking observation in the experimental work.

Funding Statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflicts of Interest

The author declares that there is no conflict of interest regarding the publication of this article.

References

1. Casanave, D., Duplan, J.L. and Freund, E., 2007. Diesel fuels from biomass. Pure and Applied Chemistry, 79(11), pp.2071-2081. doi: 10.1351/pac200779112071.DOI
2. Lloyd, A.C. and Cackette, T.A., 2001. Diesel engines: environmental impact and control. Journal of the Air &amp; Waste Management Association, 51(6), pp. 809-847. doi: 10.1080/10473289.2001.10464315.DOI
3. Tomar, M. and Kumar, N., 2020. Influence of nanoadditives on the performance and emission characteristics of a CI engine fuelled with diesel, biodiesel, and blends–a review. Energy sources, part A: Recovery, utilization, and environmental effects, 42(23), pp. 2944-2961. doi: 10.1080/15567036.2019.1623347.DOI
4. Shaafi, T., Sairam, K., Gopinath, A., Kumaresan, G., and Velraj, R., 2015. Effect of dispersion of various nanoadditives on the performance and emission characteristics of a CI engine fuelled with diesel, biodiesel and blends—a review. Renewable and Sustainable Energy Reviews, 49, pp. 563-573. doi: 10.1016/j.rser.2015.04.086.DOI
5. WHO, 2016. Ambient air pollution: A global assessment of exposure and burden of disease. W.H. Organization.
6. World Energy Outlook 2023 Free Dataset. March 2024, International Energy Agency (IEA).
7. Shine, I., 2023. The Global Biofuel Alliance has just launched, but what exactly are biofuels? W.E. Forum.
8. Kumar, R., Yadav, A.S., Sharma, A., Rajak, U., Verma, T.N., Alam, T., Tiwari, N. and Jawahar, C., 2023. Experimental analysis of a diesel engine run on non-conventional fuel blend at different preheating temperatures. Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering, pp. 09544089231190754. doi: 10.1177/0954408923119075.DOI
9. Goga, G., Mahla, S.K., Chauhan, B.S., Yadav, A.S., Chakroborty, S., Garg, J. and Garg, S.B., 2023. Predication of performance and emissions characteristics adual fuel engine energized with liquid and gaseous materials by Artificial neural network. Materials Today: Proceedings. doi: 10.1016/j.matpr.2023.01.315.DOI
10. Kumar, P., Darsigunta, A., Mouli, B.C., Sharma, V.K., Sharma, N. and Yadav, A.S., 2021. Analysis of intake swirl in a compression ignition engine at different intake valve lifts. Materials Today: Proceedings, 47, pp. 2869-2874. doi: 10.1016/j.matpr.2021.03.663.DOI
11. Rao, G.A.P. and Sharma, T.K., 2020. Engine emission control technologies: design modifications and pollution mitigation techniques. Apple Academic Press. doi: 10.1201/9780429322228.DOI
12. Ying, W., Longbao, Z. and Hewu, W., 2006. Diesel emission improvements by the use of oxygenated DME/diesel blend fuels. Atmospheric Environment, 40(13), pp. 2313-2320. doi: 10.1016/j.atmosenv.2005.12.016.DOI
13. Song, J., Cheenkachorn, K., Wang, J., Perez, J., Boehman, A.L., Young, P.J. and Waller, F.J., 2002. Effect of oxygenated fuel on combustion and emissions in a light-duty turbo diesel engine. Energy &amp; fuels, 16(2), pp.294-301. doi: 10.1021/ef010167t.DOI
14. Hosseinzadeh-Bandbafha, H., Tabatabaei, M., Aghbashlo, M., Khanali, M. and Demirbas, A., 2018. A comprehensive review on the environmental impacts of diesel/biodiesel additives. Energy Conversion and Management, 174, pp. 579-614. doi: 10.1016/j.enconman.2018.08.050.DOI
15. Shah, P.R. and Ganesh, A., 2016. A comparative study on influence of fuel additives with edible and non-edible vegetable oil based on fuel characterization and engine characteristics of diesel engine. Applied thermal engineering, 102, pp. 800-812. doi: 10.1016/j.applthermaleng.2016.03.128.DOI
16. Saxena, V., Kumar, N. and Saxena, V.K., 2017. A comprehensive review on combustion and stability aspects of metal nanoparticles and its additive effect on diesel and biodiesel fuelled CI engine. Renewable and Sustainable Energy Reviews, 70, pp.563-588. doi: 10.1016/j.rser.2016.11.067.DOI
17. Kumar, S., Dinesha, P. and Bran, I., 2019. Experimental investigation of the effects of nanoparticles as an additive in diesel and biodiesel fuelled engines: a review. Biofuels, 10(5), pp. 615-622. doi: 10.1080/17597269.2017.1332294.DOI
18. Fuskele, V. and Sarviya, R.M., 2017. Recent developments in nanoparticles synthesis, preparation and stability of nanofluids. Materials Today: Proceedings, 4(2), pp. 4049-4060. doi: 10.1016/j.matpr.2017.02.307.DOI
19. Paramashivaiah, B.M. and Rajashekhar, C.R., 2016, September. Studies on effect of various surfactants on stable dispersion of graphene nano particles in simarouba biodiesel. In IOP conference series: materials science and engineering (Vol. 149, No. 1, p. 012083). IOP Publishing.
20. [Soukht Saraee, H., Jafarmadar, S., Taghavifar, H. and Ashrafi, S.J., 2015. Reduction of emissions and fuel consumption in a compression ignition engine using nanoparticles. International journal of environmental science and technology, 12, pp. 2245-2252. doi: 10.1007/s13762-015-0759-4.DOI
21. Soni, G.S., Rathod, P.P. and Goswami, J.J., 2015. Performance and emission characteristics of CI engine using diesel and biodiesel blends with nanoparticles as additive-A review study. International Journal of Engineering Development and Research, 3(4), pp. 879-884..
22. Gupta, H.K., Agrawal, G.D. and Mathur, J., 2012. An overview of Nanofluids: A new media towards green environment. International Journal of environmental sciences, 3(1), pp.433-440. doi: 10.6088/ijes.2012030131042.DOI
23. Senthilraja, S., Karthikeyan, M. and Gangadevi, R., 2010. Nanofluid applications in future automobiles: comprehensive review of existing data. Nano-Micro Letters, 2, pp. 306-310. doi: 10.1007/BF03353859.DOI
24. Zhu, D., Li, X., Wang, N., Wang, X., Gao, J. and Li, H., 2009. Dispersion behavior and thermal conductivity characteristics of Al2O3–H2O nanofluids. Current Applied Physics, 9(1), pp. 131-139. doi: 10.1016/j.cap.2007.12.008.DOI
25. Moravej, M., Noghrehabadi, A., Esmaeilinasab, A.L.I. and Khajehpour, E., 2020. The effect of SiO2 nanoparticle on the performance of photovoltaic thermal system: Experimental and Theoretical approach. Journal of Heat and Mass Transfer Research, 7(1), pp. 11-24. doi: 10.22075/JHMTR.2020.18904.1254.DOI
26. Parvar, M., Saedodin, S. and Rostamian, S.H., 2020. Experimental study on the thermal conductivity and viscosity of transformer oil-based nanofluid containing ZnO nanoparticles. Journal of Heat and Mass Transfer Research, 7(1), pp. 77-84. doi: 10.22075/JHMTR.2020.19303.1267.DOI
27. Aminian, M.R., Miroliaei, A.R. and Mirzaei Ziapour, B., 2019. Numerical study of flow and heat transfer characteristics of CuO/H2O nanofluid within a mini tube. Journal of Heat and Mass Transfer Research, 6(1), pp. 11-20. doi: 10.22075/JHMTR.2018.14156.1205.DOI
28. Barik, A.K. and Nayak, B., 2017. Fluid flow and heat transfer characteristics in a curved rectangular duct using Al2O3-water nanofluid. Journal of Heat and Mass Transfer Research, 4(2), pp.103-115. doi: 10.22075/JHMTR.2017.1689.1115.DOI
29. Mollamahdi, M., Abbaszadeh, M. and Sheikhzadeh, G.A., 2016. Flow field and heat transfer in a channel with a permeable wall filled with Al2O3-Cu/water micropolar hybrid nanofluid, effects of chemical reaction and magnetic field. Journal of Heat and Mass Transfer Research, 3(2), pp.101-114. doi: 10.22075/JHMTR.2016.447.DOI
30. Nath, G., 2018. Physico-Acoustic Study on Thermal Conductivity of Silver Nanofluid. Journal of Heat and Mass Transfer Research, 5(2), pp. 105-110. doi: 10.22075/JHMTR.2018.12036.1175.DOI
31. Raei, B., 2021. Statistical analysis of nanofluid heat transfer in a heat exchanger using Taguchi method. Journal of heat and mass transfer research, 8(1), pp. 29-38. doi: 10.22075/JHMTR.2020.20678.1287.DOI
32. Basu, S.and Miglani, A., 2016. Combustion and heat transfer characteristics of nanofluid fuel droplets: A short review. International Journal of Heat and Mass Transfer, 96, pp. 482-503 doi: 10.1016/j.ijheatmasstransfer.2016.01.053.DOI
33. Nanthagopal, K., Ashok, B., Tamilarasu, A., Johny, A. and Mohan, A., 2017. Influence on the effect of zinc oxide and titanium dioxide nanoparticles as an additive with Calophyllum inophyllum methyl ester in a CI engine. Energy Conversion and Management, 146, pp. 8-19. doi: 10.1016/j.enconman.2017.05.021.DOI
34. Ganesh, D. and Gowrishankar, G., 2011, September. Effect of nano-fuel additive on emission reduction in a biodiesel fuelled CI engine. In 2011 International conference on electrical and control engineering (pp. 3453-3459). IEEE..
35. Hosseini, S.H., Taghizadeh-Alisaraei, A., Ghobadian, B. and Abbaszadeh-Mayvan, A., 2017. Performance and emission characteristics of a CI engine fuelled with carbon nanotubes and diesel-biodiesel blends. Renewable energy, 111, pp.201-213. doi: 10.1016/j.renene.2017.04.013.DOI
36. Hoseini, S.S., Najafi, G., Ghobadian, B., Ebadi, M.T., Mamat, R. and Yusaf, T.J.R.E., 2020. Performance and emission characteristics of a CI engine using graphene oxide (GO) nano-particles additives in biodiesel-diesel blends. Renewable Energy, 145, pp.458-465. doi: 10.1016/j.renene.2019.06.006.DOI
37. Ghanbari, M., Najafi, G., Ghobadian, B., Yusaf, T., Carlucci, A.P. and Kiani, M.K.D., 2017. Performance and emission characteristics of a CI engine using nano particles additives in biodiesel-diesel blends and modeling with GP approach. Fuel, 202, pp. 699-716. doi: 10.1016/j.fuel.2017.04.117.DOI
38. Gumus, S., Ozcan, H., Ozbey, M. and Topaloglu, B., 2016. Aluminum oxide and copper oxide nanodiesel fuel properties and usage in a compression ignition engine. Fuel, 163, pp. 80-87. doi: 10.1016/j.fuel.2015.09.048.DOI
39. Mehta, R.N., Chakraborty, M. and Parikh, P.A., 2014. Nanofuels: Combustion, engine performance and emissions. Fuel, 120, pp. 91-97. doi: 10.1016/j.fuel.2013.12.008.DOI
40. Kannan, G.R., Karvembu, R. and Anand, R.J.A.E., 2011. Effect of metal based additive on performance emission and combustion characteristics of diesel engine fuelled with biodiesel. Applied energy, 88(11), pp.3694-3703. doi: 10.1016/j.apenergy.2011.04.043.DOI
41. Ağbulut, Ü., 2022. Understanding the role of nanoparticle size on energy, exergy, thermoeconomic, exergoeconomic, and sustainability analyses of an IC engine: A thermodynamic approach. Fuel Processing Technology, 225, p. 107060. doi: 10.1016/j.fuproc.2021.107060.DOI
42. Ağbulut, Ü., Sarıdemir, S., Rajak, U., Polat, F., Afzal, A. and Verma, T.N., 2021. Effects of high-dosage copper oxide nanoparticles addition in diesel fuel on engine characteristics. Energy, 229, p.120611. doi: 10.1016/j.energy.2021.120611.DOI
43. Ağbulut, Ü., Karagöz, M., Sarıdemir, S. and Öztürk, A., 2020. Impact of various metal-oxide based nanoparticles and biodiesel blends on the combustion, performance, emission, vibration and noise characteristics of a CI engine. Fuel, 270, p.117521. doi: 10.1016/j.fuel.2020.117521.DOI
44. Roy, R.G., Ağbulut, Ü., Koshy, C.P., Alex, Y., Sailesh, K.S., Khan, S.A., Jilte, R., Linul, E. and Asif, M., 2024. Impact of synthesizing surfactant-modified catalytic ceria nanoparticles on the performance and environmental behaviors of coconut oil/diesel-fueled CI engine: An optimization attempt. Energy, 295, p.130825. doi: 10.1016/j.energy.2024.130825.DOI
45. Karagoz, M., Uysal, C., Agbulut, U. and Saridemir, S., 2021. Exergetic and exergoeconomic analyses of a CI engine fueled with diesel-biodiesel blends containing various metal-oxide nanoparticles. Energy, 214, p.118830. doi: 10.1016/j.energy.2020.118830.DOI
46. Siddartha, G.N.V., Ramakrishna, C.S., Kujur, P.K., Rao, Y.A., Dalela, N., Yadav, A.S. and Sharma, A., 2022. Effect of fuel additives on internal combustion engine performance and emissions. Materials Today: Proceedings, 63, pp.A9-A14. doi: 10.1016/j.matpr.2022.06.307.DOI
47. Hoang, A.T., Le, M.X., Nižetić, S., Huang, Z., Ağbulut, Ü., Veza, I., Said, Z., Le, A.T., Tran, V.D. and Nguyen, X.P., 2022. Understanding behaviors of compression ignition engine running on metal nanoparticle additives-included fuels: a control comparison between biodiesel and diesel fuel. Fuel, 326, p.124981. doi: 10.1016/j.fuel.2022.124981.DOI
48. Spikes, H., 2015. Friction modifier additives. Tribology Letters, 60, pp.1-26. doi: 10.1007/s11249-015-0589-z.DOI
49. Youssef, A. and Ibrahim, A., 2024. An experimental evaluation for the performance of a single cylinder CI engine fueled by a Diesel-Biodiesel blend with alcohols and Zinc-Aluminate nanoparticles as additives. Materials Today: Proceedings. doi: 10.1016/j.matpr.2024.04.015.DOI
50. Yuvarajan, D., Babu, M.D., BeemKumar, N. and Kishore, P.A., 2018. Experimental investigation on the influence of titanium dioxide nanofluid on emission pattern of biodiesel in a diesel engine. Atmospheric Pollution Research, 9(1), pp.47-52..
51. Prabakaran, B. and Udhoji, A., 2016. Experimental investigation into effects of addition of zinc oxide on performance, combustion and emission characteristics of diesel-biodiesel-ethanol blends in CI engine. Alexandria Engineering Journal, 55(4), pp.3355-3362. doi: 10.1016/j.aej.2016.08.022.DOI
52. Prabu, A., 2018. Nanoparticles as additive in biodiesel on the working characteristics of a DI diesel engine. Ain shams Engineering journal, 9(4), pp.2343-2349. doi: 10.1016/j.asej.2017.04.004.DOI
53. Sajith, V., Sobhan, C.B. and Peterson, G.P., 2010. Experimental investigations on the effects of cerium oxide nanoparticle fuel additives on biodiesel. Advances in Mechanical Engineering, 2, p.581407. doi: 10.1155/2010/581407.DOI
54. Chandrasekaran, V., Arthanarisamy, M., Nachiappan, P., Dhanakotti, S. and Moorthy, B., 2016. The role of nano additives for biodiesel and diesel blended transportation fuels. Transportation Research Part D: Transport and Environment, 46, pp.145-156. doi: 10.1016/j.trd.2016.03.015.DOI
55. Jayanthi, P. and Rao, M.S., 2016. Effects of nanoparticles additives on performance and emissions characteristics of a DI diesel engine fuelled with biodiesel. International Journal of Advances in Engineering &amp; Technology, 9(6), p.689. doi: 10.7323/ijaet/v9_iss6.DOI
56. Annamalai, M., Dhinesh, B., Nanthagopal, K., SivaramaKrishnan, P., Lalvani, J.I.J., Parthasarathy, M. and Annamalai, K., 2016. An assessment on performance, combustion and emission behavior of a diesel engine powered by ceria nanoparticle blended emulsified biofuel. Energy conversion and management, 123, pp.372-380. doi: 10.1016/j.enconman.2016.06.062.DOI
57. Devarajan, Y., Munuswamy, D.B. and Mahalingam, A., 2017. Performance, combustion and emission analysis on the effect of ferrofluid on neat biodiesel. Process Safety and Environmental Protection, 111, pp.283-291. doi: 10.1016/j.psep.2017.07.021.DOI
58. Shaafi, T. and Velraj, R.J.R.E., 2015. Influence of alumina nanoparticles, ethanol and isopropanol blend as additive with diesel–soybean biodiesel blend fuel: Combustion, engine performance and emissions. Renewable Energy, 80, pp.655-663. doi: 10.1016/j.renene.2015.02.042.DOI
59. Özgür, T., Özcanli, M. and Aydin, K., 2015. Investigation of nanoparticle additives to biodiesel for improvement of the performance and exhaust emissions in a compression ignition engine. International journal of green energy, 12(1), pp.51-56. doi: 10.1080/15435075.2014.889011.DOI
60. Aalam, C.S., Saravanan, C.G. and Kannan, M., 2015. Experimental investigations on a CRDI system assisted diesel engine fuelled with aluminium oxide nanoparticles blended biodiesel. Alexandria engineering journal, 54(3), pp.351-358. doi: 10.1016/j.aej.2015.04.009.DOI
61. Sadhik Basha, J. and Anand, R.B., 2013. The influence of nano additive blended biodiesel fuels on the working characteristics of a diesel engine. Journal of the Brazilian Society of Mechanical Sciences and Engineering, 35, pp.257-264. doi: 10.1007/s40430-013-0023-0.DOI
62. Gürü, M., Karakaya, U., Altıparmak, D. and Alıcılar, A., 2002. Improvement of diesel fuel properties by using additives. Energy conversion and Management, 43(8), pp.1021-1025. doi: 10.1016/S0196-8904(01)00094-2.DOI
63. Vellaiyan, S. and Partheeban, C.A., 2020. Combined effect of water emulsion and ZnO nanoparticle on emissions pattern of soybean biodiesel fuelled diesel engine. Renewable Energy, 149, pp.1157-1166. doi: 10.1016/j.renene.2019.10.101.DOI
64. Choi, Y., Lee, C., Hwang, Y., Park, M., Lee, J., Choi, C. and Jung, M., 2009. Tribological behavior of copper nanoparticles as additives in oil. Current Applied Physics, 9(2), pp. e124-e127. doi: 10.1016/j.cap.2008.12.050.DOI
65. Mortier, R.M., Orszulik, S.T. and Fox, M.F., 2010. Chemistry and technology of lubricants. Vol. 107115. Springer. doi: 10.1007/978-1-4020-8662-5.DOI
66. Barnes, A.M., Bartle, K.D. and Thibon, V.R., 2001. A review of zinc dialkyldithiophosphates (ZDDPS): characterisation and role in the lubricating oil. Tribology international, 34(6), pp.389-395. doi: 10.1016/S0301-679X(01)00028-7.DOI
67. Rudnick, L.R., 2009. Lubricant additives: chemistry and applications. CRC press. doi: 10.1201/9781420059656.DOI
68. Bakunin, V.N., Suslov, A.Y., Kuzmina, G.N., Parenago, O.P. and Topchiev, A.V., 2004. Synthesis and application of inorganic nanoparticles as lubricant components–a review. Journal of Nanoparticle Research, 6, pp.273-284. doi: 10.1023/B:NANO.0000034720.79452.e3.DOI
69. Li, X., Cao, Z., Zhang, Z. and Dang, H., 2006. Surface-modification in situ of nano-SiO2 and its structure and tribological properties. Applied surface science, 252(22), pp.7856-7861. doi: 10.1016/j.apsusc.2005.09.068.DOI
70. Battez, A.H., González, R., Viesca, J.L., Fernández, J.E., Fernández, J.D., Machado, A., Chou, R. and Riba, J., 2008. CuO, ZrO2 and ZnO nanoparticles as antiwear additive in oil lubricants. Wear, 265(3-4), pp.422-428. doi: 10.1016/j.wear.2007.11.013.DOI
71. Cellard, A., Garnier, V., Fantozzi, G., Baret, G. and Fort, P., 2009. Wear resistance of chromium oxide nanostructured coatings. Ceramics International, 35(2), pp.913-916. doi: 10.1016/j.ceramint.2008.02.022.DOI
72. Hwang, Y., Lee, C., Choi, Y., Cheong, S., Kim, D., Lee, K., Lee, J. and Kim, S.H., 2011. Effect of the size and morphology of particles dispersed in nano-oil on friction performance between rotating discs. Journal of Mechanical Science and Technology, 25, pp.2853-2857. doi: 10.1007/s12206-011-0724-1.DOI
73. Ali, Z.A.A.A., Takhakh, A.M. and Al-Waily, M., 2022. A review of use of nanoparticle additives in lubricants to improve its tribological properties. Materials Today: Proceedings, 52, pp.1442-1450. doi: 10.1016/j.matpr.2021.11.193.DOI
74. Waqas, M., Zahid, R., Bhutta, M.U., Khan, Z.A. and Saeed, A., 2021. A review of friction performance of lubricants with nano additives. Materials, 14(21), p.6310. doi: 10.3390/ma14216310.DOI
75. Shahnazar, S., Bagheri, S. and Abd Hamid, S.B., 2016. Enhancing lubricant properties by nanoparticle additives. International journal of hydrogen energy, 41(4), pp.3153-3170. doi: 10.1016/j.ijhydene.2015.12.040.DOI
76. Srivyas, P.D. and Charoo, M.S., 2018. A Review on Tribological Characterization of Lubricants with Nano Additives for Automotive Applications. Tribology in Industry, 40(4). doi: 10.24874/ti.2018.40.04.08.DOI
77. Wu, Y.Y., Tsui, W.C. and Liu, T.C., 2007. Experimental analysis of tribological properties of lubricating oils with nanoparticle additives. Wear, 262(7-8), pp. 819-825. doi: 10.1016/j.wear.2006.08.021.DOI
78. Mangam, V., Bhattacharya, S., Das, K. and Das, S., 2010. Friction and wear behavior of Cu–CeO2 nanocomposite coatings synthesized by pulsed electrodeposition. Surface and Coatings Technology, 205(3), pp.801-805. doi: 10.1016/j.surfcoat.2010.07.119.DOI
79. Jiao, D., Zheng, S., Wang, Y., Guan, R. and Cao, B., 2011. The tribology properties of alumina/silica composite nanoparticles as lubricant additives. Applied Surface Science, 257(13), pp.5720-5725. doi: 10.1016/j.apsusc.2011.01.084.DOI
80. Battez, A.H., Viesca, J.L., González, R., Blanco, D., Asedegbega, E. and Osorio, A., 2010. Friction reduction properties of a CuO nanolubricant used as lubricant for a NiCrBSi coating. Wear, 268(1-2), pp.325-328. doi: 10.1016/j.wear.2009.08.018.DOI
81. Song, X., Zheng, S., Zhang, J., Li, W., Chen, Q. and Cao, B., 2012. Synthesis of monodispersed ZnAl2O4 nanoparticles and their tribology properties as lubricant additives. Materials Research Bulletin, 47(12), pp.4305-4310. doi: 10.1016/j.materresbull.2012.09.013.DOI
82. Shi, G., Zhang, M.Q., Rong, M.Z., Wetzel, B. and Friedrich, K., 2004. Sliding wear behavior of epoxy containing nano-Al2O3 particles with different pretreatments. Wear, 256(11-12), pp.1072-1081. doi: 10.1016/S0043-1648(03)00533-7.DOI
83. Kirloskar Oil Engines Limited. 2024, [05-05-2024], Available from:Publisher Full Text
84. Castrol GTX Diesel 15W-40. October 2023 [05-05-2024]; Available from:Publisher Full Text
85. BANDELIN electronic GmbH &amp; Co. KG Germany. [cited 2024 17th May]; Available from:Publisher Full Text
86. ASTM, D 446 : Standard Speci®cations and Operating Instructions for Glass Capillary Kinematic Viscometers, 1999. ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States..