An Experimental Investigation on Tribological Behaviour of Tire-Derived Pyrolysis Oil Blended with Biodiesel Fuel

: The demand for alternative fuels has risen in recent years due to the economic and environmental consequences of conventional fuels. In addition to engine characteristics, i.e., performance, combustion, and emission the lubricity of the considered fuel is an important parameter for its selection. This experimental study shows the tribological performance of the tire pyrolysis oil by using the four-ball tester. Waste tire pyrolysis oil was puriﬁed by using the distillation process. The experiment was conducted over 300 s at 40, 50, 63, and 80 kg load, 1800 rpm constant speed, and 27 ◦ C temperature of all fuels on the ASTM D2266 standard. The tribological performance of the tire pyrolysis oil was compared with the BT10 (biodiesel 90%–tire pyrolysis oil 10%) and BT20 (biodiesel 80%–tire pyrolysis oil 20%) and biodiesel. The optical microscope is used to measure the wear scar diameter and then it is examined through a scanning electron microscope. In terms of greater load-carrying capacity, tire pyrolysis oil shows better anti-wear behaviour compared to biodiesel fuel. The wear scar diameter of BT10, BT20, and tire pyrolysis oil was 23.99%, 8.37%, and 32.62%, respectively, lower than the biodiesel fuel at 80 kg load. The SEM micrographs revealed that tire pyrolysis oil and BT10 displayed lower wear as compared to counterparts. Finally, it is concluded that BT10 is the most suitable fuel in terms of tribological performance. enhance lubricity is flash temperature. A higher FTP value leads to better lubricating performance and reduced risks of lubricant film breakdown [47]. The FTP value for each tested fuel rises with a reduction in the wear load. The findings show that the load increase appears to increase the worn surface’s WSD as well and FTP is inversely proportional to wear scar diameter [48]. Compared to other fuels, TPO displayed the highest FTP of 25.67 °C at 80 kg load. The better FTP results are shown by BT10 and BT20 and that is similar to biodiesel fuel. However, biodiesel fuel (14.77 °C) has been credited with the lowest FTP


Introduction
The extinction of fossil fuels, climate change, economic recession, surges in population growth, increasing demand, and declining supply of fuel have highlighted the significance of alternative fuels [1,2]. Two main forms of alternative renewable fuels are food and waste based. Food-based fuels include sunflower, palm oil, and rapeseed, etc. These could result in global issues like deforestation and food shortages worldwide and thus received a lot of criticism [3]. Waste-based fuels and microalgae biodiesel are non-food-based fuels and have very potential as an alternative fuel [4]. However, waste-based fuels are the most potent alternative fuels that can replace conventional fossil fuels [5]. On the other hand, the dumping of solid waste tires results in a plethora of environmental issues [6,7]. According to a report by the European Automotive Manufacturers Association (EAMA), there are

Tire Pyrolysis Oil Production and Purification
The pyrolysis process is used to convert the waste tires to tire pyrolysis oil (49%), solid char (44%), and pyrolytic gas (7%) respectively. The waste tires were condensed and their flow rate differed from 5.5 to 14.5 kg/h [12]. The physicochemical properties of raw tire pyrolysis oil are listed in Table 2. It is reported that the viscosity, density, flash point, and calorific value of waste TPO is similar to automotive diesel, but the amount of sulphur is substantially higher than the diesel [20]. The presence of an excess quantity of oxygen content (0.10-3.96%) in TPO [7] and 10.79% in biodiesel [43] can minimize friction and wear as compared to diesel [44]. The purification of waste TPO was completed in the research facility. Towards the beginning, waste TPO was warmed at 110 • C to eliminate its water content. At this point, 8% H 2 SO 4 was added to the waste TPO for the hydro sulfuric acid treatment at 70 • C and mixed with a magnetic stirrer for 4 h. After this cycle, the blend was left for 48 h. At last, the blend was run through a distillation unit. The biodiesel fuel was acquired from a local organization. BT10 and BT20 blends were made by utilizing the magnetic stirrer. The physical properties of biodiesel fuel, BT10, BT20, and tire pyrolysis oil (TPO) are presented in Table 3. The apparatuses utilized in this work are recorded in Table 4.

Test Setup
Four ball tribometer (TR-30L-IAS, DUCOM, Bengaluru, Karnataka, India) was utilized during the examination that aided in the research and development of tribology of new oils (shown in Figure 1). It utilized four balls to test the sample however three of those were fixed in the fuel sample bath and one ball was turning that was held by the motor spindle. The schematic diagram of the four-ball tester and the exploratory setup appears in Figure 2. The fuel/oil bath was loaded up with the tested fuel. The highlights of the fourball tester are recorded in Table 5.    The lever arm was utilized to apply loads on the balls fixed at the bottom and frictional torque was determined by the balanced arm utilizing a spring connected to a friction recording apparatus. The carbon-chromium steel balls were utilized in this investigation and the details of the balls are recorded in Table 5. Four new balls were cleaned with acetone and dried using air and tissue paper.   The lever arm was utilized to apply loads on the balls fixed at the bottom and frictional torque was determined by the balanced arm utilizing a spring connected to a friction recording apparatus. The carbon-chromium steel balls were utilized in this investigation and the details of the balls are recorded in Table 5. Four new balls were cleaned with acetone and dried using air and tissue paper.

Test Procedure
Acetone was used to clean the four steel balls and oil cups to remove the dust particles and oil before each experiment. In accordance with the recommended torque, the 03 steel balls were locked in the cup, and then test oil was poured into the oil cup until the 03 steel balls were completely covered. 01 ball clutched and then fixed within the apparatus. The oil cup was placed inside the apparatus and the controller cable was attached to it. ASTM standard D2266 was used for these experiments. The duration was 300 s at 1800 rpm constant spindle speed with 40, 50, 63, and 80 kg loads at an oil temperature of 27 • C. The software (Winducom 2010) was used to measure and evaluate the readings at the decided varying parameters. Table 6 shows the experimental requirements for four-ball experiments. The three steel balls in the oil cup were acquired at the end of the experiment to measure the wear scar's diameter using an optical microscope and for SEM study.

Friction Evaluation
The software (Winducom 2010) used in the measurement of the value of friction's mean coefficient by using the Equations (1) and (2) [38]. Frictional torque is measured by using a load cell in the apparatus.
where µ is the friction coefficient, T is the frictional torque (N.m), W is the applied load (N) and r is the distance defined to be 3.67 mm from the middle of the contact surface on the lower balls to the rotation axis.

Flash Temperature Parameter
The flash temperature parameter (FTP) of all fuels were measured using Equation (3) [38]. It is an important parameter for the lubricants to portray the critical flash temperature under the input conditions of the four-ball test.
where F is the applied load (kg) and D is the average WSD (mm).

Wear Evaluation
As per standard ASTM D4172, the optical microscope was used to measure the wear scar diameter of the steel balls at a resolution of 0.01 mm. [38]. The optical microscope used the computer's software (Scar View 2005) to capture the wear scar image. In addition, the wear scar diameter using this Scar View 2005 was measured.

Friction Behaviour
The frictional performance was unstable due to the run-in period of the testing at the start of the experiment. The balanced friction behaviour was reported after a couple of seconds and it is called the steady-state condition. The steady-state point is reached over time. This result is due to the fact that, at the start, the surface layer is scratchy. The surface of the tested balls is smoothed a few minutes later by eliminating prominent asperity. The run-in period coefficient of friction was shown in the first 10 s, and the mean steady-state coefficient of friction for the last 100 s was recorded and presented in Figure 3. the steady-state condition. The steady-state point is reached over time. This result is due to the fact that, at the start, the surface layer is scratchy. The surface of the tested balls is smoothed a few minutes later by eliminating prominent asperity. The run-in period coefficient of friction was shown in the first 10 s, and the mean steady-state coefficient of friction for the last 100 s was recorded and presented in Figure 3. Biodiesel is shown to have a relatively higher run-in period friction coefficient over a longer period of time than the other fuel samples. TPO produces better friction protection performance than biodiesel and blended fuel samples. Mello et al. reported [21] that the higher sulphur content tends to increase the lubricity. Therefore, TPO performs better lubricity performance due to higher sulphur content as compared to biodiesel fuel that is why TPO, BT10, and BT20 shown an unsteady friction coefficient of 41, 49.66, and 28.63% respectively, lower than biodiesel fuel. In contrast to biodiesel TPO, BT10 and BT20 displayed a smooth mechanism of the steady-state coefficient of friction that confirms a fluctuating pattern.
Wain et al. [44] stated that biodiesel containing more oxygen can minimize friction and wear. The coefficient of friction performance of BT10 and BT20 is relatively similar to biodiesel fuel in the Biodiesel is shown to have a relatively higher run-in period friction coefficient over a longer period of time than the other fuel samples. TPO produces better friction protection performance than biodiesel and blended fuel samples. Mello et al. reported [21] that the higher sulphur content tends to increase the lubricity. Therefore, TPO performs better lubricity performance due to higher sulphur content as compared to biodiesel fuel that is why TPO, BT10, and BT20 shown an unsteady friction coefficient of 41, 49.66, and 28.63% respectively, lower than biodiesel fuel. In contrast to biodiesel TPO, BT10 and BT20 displayed a smooth mechanism of the steady-state coefficient of friction that confirms a fluctuating pattern.
Wain et al. [44] stated that biodiesel containing more oxygen can minimize friction and wear. The coefficient of friction performance of BT10 and BT20 is relatively similar to biodiesel fuel in the case of a steady-state condition. According to the test conditions adopted at the boundary, the viscosity of lubricating oils is the key parameter that affects the film thickness separating the surfaces and therefore determines the friction behaviour [45]. In view of the importance of the viscosity of the lubricating oil considered, higher temperatures were observed in the fourball contact geometry, resulting in a reduction in the viscosity of the oil and a higher average coefficient of friction. The comparison of friction profiles therefore showed poor TPO friction activity.

Wear Behaviour
The metal to metal contact contributes to the battering of the collaborating tribo-pair under minimal grease conditions. Figure 4 demonstrates the wearing actions of all of the tested fuel considered. The investigation clearly shows that a bad anti-wear mechanism has been demonstrated by TPO at low loads such as 40, 50, and 63 kg. However, better wear prevention is noticed by TPO at a higher load of 80 kg. This pattern has shown the high load carrying limit of TPO. The potential rises in contact temperatures at higher loads resulted in low viscous oils that enhanced the chances of tribo-pair surface contact. As compared with BD, TPO, and BT20 at both low and high loads, BT10 demonstrated a better anti-wear mechanism. The WSD of BT10, BT20, and TPO was 23.99, 8.37, and 32.62% respectively that was lower than the biodiesel fuel at the 80 kg load. High sulphur content in TPO reduces the wear behaviour and their blend with biodiesel helps to increase the lubricating properties [46]. Biodiesel has no sulphur content that caused the problems in the lubricity, but Mello et al. also reported [21] that the higher sulphur content tends to increase the lubricity.
in contact temperatures at higher loads resulted in low viscous oils that enhanced the chances of tribo-pair surface contact. As compared with BD, TPO, and BT20 at both low and high loads, BT10 demonstrated a better anti-wear mechanism. The WSD of BT10, BT20, and TPO was 23.99, 8.37, and 32.62% respectively that was lower than the biodiesel fuel at the 80 kg load. High sulphur content in TPO reduces the wear behaviour and their blend with biodiesel helps to increase the lubricating properties [46]. Biodiesel has no sulphur content that caused the problems in the lubricity, but Mello et al. also reported [21] that the higher sulphur content tends to increase the lubricity.

Flash Temperature Parameter
The result of tested fuels on the flash temperature parameter (FTP) is presented in Figure 5. Strong lubricating efficiency and a low chance of lubricant layer breakdown lead to a high FTP value. The temperature at which a lubricating layer can be formed to enhance lubricity is flash temperature. A higher FTP value leads to better lubricating performance and reduced risks of lubricant film breakdown [47]. The FTP value for each tested fuel rises with a reduction in the wear load. The findings show that the load increase appears to increase the worn surface's WSD as well and FTP is inversely proportional to wear scar diameter [48]. Compared to other fuels, TPO displayed the highest FTP of 25.67 °C at 80 kg load. The better FTP results are shown by BT10 and BT20 and that is similar to biodiesel fuel. However, biodiesel fuel (14.77 °C) has been credited with the lowest FTP

Flash Temperature Parameter
The result of tested fuels on the flash temperature parameter (FTP) is presented in Figure 5. Strong lubricating efficiency and a low chance of lubricant layer breakdown lead to a high FTP value. The temperature at which a lubricating layer can be formed to enhance lubricity is flash temperature. A higher FTP value leads to better lubricating performance and reduced risks of lubricant film breakdown [47]. The FTP value for each tested fuel rises with a reduction in the wear load. The findings show that the load increase appears to increase the worn surface's WSD as well and FTP is inversely proportional to wear scar diameter [48]. Compared to other fuels, TPO displayed the highest FTP of 25.67 • C at 80 kg load. The better FTP results are shown by BT10 and BT20 and that is similar to biodiesel fuel. However, biodiesel fuel (14.77 • C) has been credited with the lowest FTP rating at 80 kg, because of the biodiesel deterioration. Hence, the contact surfaces surround each other and enhance the surface of the contact [49].

Morphological Analysis
Tested ball worn surfaces were characterized by scanning electron microscopy (SEM) to understand the anti-wear behaviour of considered fuel samples. The related worn surfaces were also analysed using SEM, TPO showed better wear prevention at higher loads (80 kg). For the fuel samples tested, Figure 6a-l displays the SEM micrographs of the worn surfaces of the tested balls under 80 kg. The micrographs of the biodiesel showing adhesive wear and rough surface area as clear in Figure  6a-c above the TPO blended samples Figure 6d-l. Similarly, the least material removal is presented in Figure 6d-f relative to Figure 6g-l. For all tested fuels, the surface wear is greater than 20 μm, thus representing adhesive wear [50]. As the TPO blend ratio increases, the wear scar diameter leads to an increase. The SEM images also demonstrate that the metal layers are separated from the surfaces in

Morphological Analysis
Tested ball worn surfaces were characterized by scanning electron microscopy (SEM) to understand the anti-wear behaviour of considered fuel samples. The related worn surfaces were also analysed using SEM, TPO showed better wear prevention at higher loads (80 kg). For the fuel samples tested,  Figure 6d-f relative to Figure 6g-l. For all tested fuels, the surface wear is greater than 20 µm, thus representing adhesive wear [50]. As the TPO blend ratio increases, the wear scar diameter leads to an increase. The SEM images also demonstrate that the metal layers are separated from the surfaces in the direction in which the spinning ball rotates. Wain et al. reported that [44] the alternative fuels that have oxygen content may contribute to lower diesel engine emissions but compared to higher sulphur fuels, they may also have lower anti-wear properties.

Conclusions
This experimental study identifies the tribological performance of the tire-derived pyrolysis oil blended with biodiesel fuel by using a fourball tester. The experiment was conducted over 300 s at 40, 50, 63, and 80 kg load, 1800 rpm constant speed, and 27 • C temperature of all fuels on the ASTM D2266 standard. The tribological performance of the TPO was compared with the BT10 (Biodiesel 90%, TPO 10%) and BT20 (Biodiesel 80%, TPO 20%) and biodiesel. Fourball tester is a basic test rig that is generally used in the lubricant industry to assist with new lubricant or grease research and growth. Therefore, it is used to study the tribological performance of the TPO blended with biodiesel fuel. The major findings of this experimental study are as follows: 1.
BT10, BT20, and TPO have 49.66%, 28.63%, and 41% lower unsteady coefficient of friction, respectively, than biodiesel. In contrast to the variable performance of biodiesel fuel, the BT10 and TPO showed a smooth behaviour of the unsteady friction coefficient.

2.
In comparison to biodiesel fuel, at low and high loads, TPO and BT10 exhibit better wear patterns. The WSD of TPO, BT10, and BT20 were as 32.62%, 23.99% and 8.37%, respectively, lower than the biodiesel fuel at 80 kg load. The higher sulphur content in the TPO shows better anti-wear behaviour. 3.
TPO demonstrates a higher load-carrying capacity that reflects its ability to be used in higher loads and extreme situations of pressure. 4.
The wear behaviour of fuel blends tested suggests that for a particular application, moderate friction behaviour, as well as higher load-carrying capacity, can be achieved.

5.
Compared to other fuels, TPO has a maximum FTP of 25.67 • C at 80 kg load. The FTP results shown by BT10 and BT20 are similar to biodiesel fuel at low loads but a better performance of BT10 and BT20 at high loads. However, biodiesel fuel (14.77 • C) was rated with the lowest FTP value. 6.
The SEM micrographs revealed that BT10 and BT20 showed lower metal extrusion compared to biodiesel fuel. Morphology showed that biodiesel fuel particles are broad and are shortened with the rise in the percentage of TPO.
The result of the study suggests that in terms of friction and wear BT10 showed favourable tribological performance. Therefore, it can be used to enhance an engine's life. In addition, tire pyrolysis oil blended with various oils (Fat oil biodiesel, jatropha biodiesel, microalgae biodiesel, and plastic oil etc.) could be used in future work to reduce engine wear. To increase the tribological efficiency, various additives and nanoparticles may be added to increase the desired properties in the TPO blended fuel.