Thermal Behavior Characteristics of Vegetable Oil under Various Rotational Speeds

Younus FA, Jabal MH and Ismael SA

Published on: 2023-10-23


Not long ago, research and studies tended towards the possibility of using vegetable and plant oils in engineering and industrial applications and using them as cooling oils because they are a renewable, natural resource and have a high biodegradability compared to commercial mineral oils. In this paper, vegetable oil (sunflower seed oil) is presented as a renewable cooling fluid by assessing the thermal performance of sunflower oil under different conditions. The rotary ball-on-disk machine was used for the 60-minute test, conducted at rotational speeds of 1000, 1200, and 1400 rpm with a fixed average load of 100 N and an ambient temperature of 27 °C. All tests in this work were done according to the American Society for Testing and Materials standard (ASTM-G99). The results exhibited that sunflower seed oil has a lower value of the coefficient of friction, friction force, and flash temperature parameters (0.0122, 1.233, and 32.62, respectively) compared to 0.1381, 1.3935, and 33.2125, respectively, for the commercial mineral oil. It has a high value for the wear scar diameter (438.93 µm compared with 433.6µm for the mineral oil sample). In conclusion, the vegetable sample oil (sunflower seed oil) performs adequately compared to a commercial mineral fluid sample.


Thermal performance; Sunflower oil; Flash temperature; Ball on disk; Mineral oil


In recent years, there has been a notable surge in interest regarding the potential use of vegetable oils as a substitute for mineral oils in diverse industrial applications. This is primarily due to the high costs of oil extraction, the depletion of reserves, and growing environmental apprehensions. Scholars have investigated substitute alternatives that facilitate utilizing sustainable, organic resources in producing lubricants with similar characteristics. This study explores the viability of utilizing sunflower seed oil as an eco-friendly coolant by evaluating its thermal stability and tribological characteristics across varying circumstances. [1]. There exist notable variations in the composition of pyrolytic oil among various vegetable oils, including but not limited to sunflower, coconut, jatropha, rapeseed, and palm. [2]. Vegetable oils offer numerous advantages, such as eco-friendliness, widespread accessibility, and renewable nature [3]. The ball tribometer assessed the tribological characteristics of refined, bleached, and deodorized palm olein (RBD). Studies have demonstrated that RBD palm oil exhibits reduced friction coefficients compared to mineral oil. The study found that the wear diameter of the spherical bearing lubricated with vegetable oil exhibited a greater value than the sample lubricated with mineral lubricant [4]. Additionally, it has been noted in reference [5]. At elevated temperatures, the coconut oil's diameter may experience an increase, concomitant with a decrease in the coefficient of friction. The outcome above can be attributed to the fatty acids in coconut oil. The inspection of mustard seed oil, blends, and mineral oils has been conducted following the ASTM D4172-B standard. The study's findings indicate that incorporating mineral oil into mustard seed oil decreased the friction coefficient and wear diameter and reduced the flash temperature coefficient [6]. The quest for plant-based working fluids as potential alternatives to petroleum oils can be categorized into four primary series. The initial set of experiments centered on uncontaminated vegetable oil samples [7–8], whereas the next set centered on vegetable oil emulsions [9]. The efficacy of plant oil supplemented with additives has been subjected to three rounds of testing. [10] The fourth instalment of the series centered on the advantages of incorporating vegetable oil as a constituent. [11–12]. The temperature coefficient measures the rate of change of physical property for temperature.                                               

The quest for plant-derived functional fluids as viable replacements for petroleum-based oils has been classified into four main categories: pure extracts of vegetable oil, vegetable oil emulsions, plant oil with incorporated additives, and vegetable oil as an ingredient.

The current research aims to empirically examine sunflower seed oil's tribological characteristics and thermal stability as a potential substitute for mineral oils. The utilization of sunflower seed oil as a potential substitute for mineral oils has garnered significant attention due to its favourable attributes, including its cost-effectiveness, sustainability, and efficacy as an active energy source. This alternative energy source shows excellent potential, particularly in regions with high temperatures. This study aims to gain insights into the potential advantages of utilizing sunflower seed oil as a sustainable cooling fluid by evaluating its tribological properties across various conditions.                                                    

The present study presents a comprehensive survey of the existing literature regarding using vegetable oils to replace mineral oils in diverse industrial contexts. The primary emphasis is on these oils' tribological characteristics and thermal stability. The research aims to experimentally examine the characteristics of sunflower seed oil as a renewable cooling fluid. This is due to its potential as a viable, eco-friendly, and cost-effective mineral oil substitute. The results obtained from this investigation have the potential to facilitate the advancement of vegetal-derived functional fluids for industrial purposes, offering a substitute for non-renewable and ecologically detrimental petroleum-based oils.

Experimental Work Systematics

Rotary Ball on Disk Machine

Understanding the behavior of oils, transmission fluids, and other fluids in various experimental settings has become increasingly important. The emergence of new technologies and applications, including advanced lubricants, composites, and automotive systems, has rendered traditional tribometers and measurement systems obsolete. To address this need, a modular testing system, the rotary ball on disk machine, was developed to enable fluid tests for tribological evaluation under diverse test conditions. The capabilities of this adaptable meter surpass current requirements, and it is equipped with a rotary drive that regulates disk rotation. The counter specimen is securely held in a friction or loading arm and can take any custom shape, such as a ball. A known load is applied to the counter specimen to generate the required contact stress. The Ball-on-Disk machine is an entirely computer-controlled testing apparatus. The Acquire Control and Data Acquisition System allows users to select and establish the desired test parameters, such as oil type, load, temperature, and speed. It presents the test results along with the test settings. For this study, we evaluated two types of fluids: sunflower seed oil (SFO) and commercial mineral fluid (CMF).

Figure1: Rotary Ball-On-Disk Machine.

Frictional Force and Coefficient of Friction

Using a particular data-gathering technique, the friction force from the ball-on-disk tribometer was measured over an hour. At the start of the test, the friction force for all test oils rose quickly to 300 sec. After 300 seconds, the data on the friction force reached a stable and steady-state condition. Equation (1) shows the friction coefficient calculated following IP-239 using the average friction force measured at steady-state conditions.

μ=F/N                         (1)

Where denotes the coefficients of friction (μ), F is the frictional force in Newton’s, and N denotes the applied loads in Newton’s. The identical calculating procedure was employed by [14, 15].

Flash Temperature Parameter

The critical temperature that oil must reach before failing is described by this dimensionless parameter. The FTP can be used to calculate the equation [2].

Results And Discussions

The study aimed to examine the thermal behavior properties of sunflower seed oil, a sustainable bio-oil, and commercial mineral oil. A viscometer machine was utilized to evaluate the relationship between viscosity and temperature. Furthermore, a ball-on-disk apparatus assessed the frictional force, wear scar diameter, friction coefficient, and temperature flash parameters under varying rotational velocities (1000, 1200, and 1400 rpm). The findings were illustrated in Figures 2-6 and analyzed thoroughly. According to the results, both oils demonstrate conventional Newtonian characteristics, wherein the viscosity decreases with a temperature rise. Sunflower seed oil exhibits consistently better viscosity than commercial mineral oil. The findings obtained from the ball-on-disk apparatus indicate that sunflower seed oil exhibits a more significant coefficient of friction and wear than commercially available mineral oil.

By comparison, the temperature flash measurements obtained for sunflower seed oil exceeded those recorded for commercial mineral oil. In addition, elevating the angular velocity of the ball on the disk apparatus resulted in a decrease in the friction coefficient and the diameter of the wear scar for both lubricants. The decline observed was comparatively more substantial for sunflower seed oil than commercial mineral oil. The results generally suggest sunflower seed oil displays unique thermal properties compared to conventional mineral oils. The findings of this study could potentially have significant ramifications for using sunflower seed oil as a sustainable bio-oil in diverse industrial contexts. Additional investigation is required to ascertain the appropriateness of substituting sunflower seed oil for conventional mineral oil in particular industrial contexts.

Viscosity - Temperature Relationship

The viscosity of oils is a significant feature that affects the performance of machines and engines, directly or indirectly. This work investigated the kinetic viscosity of the oil samples using a rotational viscometer and a range of temperatures. Figure 2 shows the test's findings about the relationship between viscosity and temperature.

Figure 2: Viscosity - Temperature Relationship.

One can see from this graph that the temperature and viscosity for both oil samples have an inverse connection (plant and mineral oil). From the same picture, it was also possible to see that the viscosity values for both types of oils—sunflower and mineral oil—converge at high temperatures. Indirectly depicted in Figure 2 is that vegetable oil (sunflower oil) has a higher viscosity index value than mineral oil [16].

This result indicates the possibility of substituting vegetable oil for mineral oil as engine oil because it is complicated to start a cold engine with high-viscosity oil, i.e., more work is required to pump it and shear it between moving parts—more excellent friction work results from this, which speeds up fuel consumption. However, fluid viscosity increases are necessary for maintaining and improving engine performance at higher operating temperatures. Mineral-based fluid is frequently used for systems because it offers many valuable qualities, such as lubricating, anti-wear, and friction capabilities. Petroleum fluid is thoroughly refined for these uses to eliminate other compounds, such as additives, which were added to the oil to improve performance while undesired substances were removed. One of these performance measures is viscosity and its associated index. Because it fluctuates with temperature, oil viscosity is always given at a reference temperature, usually 100°C or 25°C.

Wear Scars Diameter

In Fig. 3, the diameter of the wear scar was calculated and plotted graphically. Scar diameter increases with increasing rotational speed for both oil samples (sunflower and mineral oil) and sunflower and mineral oils behave similarly for most values of velocities (438.933 μm and 433.6 μm for sunflower oil and mineral oil, respectively, below 1200 rpm; and 483.56 µm and 442.566 µm for sunflower and liquid metal, respectively, below 1400 rpm). It was also observed that the values of the diameter of the scar in the vegetable oil were close to the values of the diameter of the mineral oil.

Figure 3: Relationship of the Wear Scar Diameter Values at Different Rotational Speeds.

Frictional Force and Coefficient of Friction

The present study investigated the relationship between friction force and friction coefficient concerning the velocity of two liquid samples, sunflower oil and mineral oil. The results reveal that friction force and friction coefficient positively correlate with velocity for each liquid sample. Furthermore, it was observed that sunflowers and mineral oil exhibit similar behaviour for most velocity values. Figure 4 depicts an increase in friction force with increasing speed, as indicated by values of 1.23666 N and 1.37345 N for sunflower and mineral oil, respectively, below 1000 rpm; 1.23334 N and 1.39352 N for sunflower and mineral oil, respectively, below 1200 rpm; and 1.51194 N and 1.62339 N for sunflower and mineral oil, respectively, below 1400 rpm. Similarly, Figure 5 demonstrates an increase in friction coefficient with speed, with values of 0.01227 and 0.01357 for sunflower and mineral oil, respectively, below 1000 rpm; 0.01223 and 0.01382 for sunflower and mineral oil, respectively, below 1200 rpm; and 0.01496 and 0.01605 for sunflower and mineral oil, respectively, below 1400 rpm. Additionally, it was noted that the friction force and friction coefficient values for sunflower oil were consistently lower than those for mineral oil across all speeds examined.

Figure 4: Frictional Force Values under Different Rotational Speeds.

Figure 5: Coefficient of Friction Values under Different Rotational Speeds.

Flash Temperature Parameter

The flash temperature, commonly referred to as the "temperature parameters for flash" (FTP), is a critical property that needs to be determined for oils. This property indicates the oil's ability to withstand testing or operational conditions before breaking down [17]. In particular working environments, a high flash temperature is perceived as a desirable characteristic of the fluid's effectiveness.

To compute the temperature parameters for flash (FTP) for the fluid samples, sunflower oil, and mineral oil, the diameters of the worn area were measured at different rotating speeds, and Equation 2 was used. The FTP values were graphically represented in Figure 6. The results demonstrate that both sunflower oil and mineral oil exhibit a decrease in their FTP values as the rotational speed increases. For most of the speed values, the performance of the vegetable and mineral oils was similar. Specifically, the FTP values for sunflower oil and mineral oil were 37.208 and 38.1635, respectively, under 1000 rpm, while the FTP values for vegetable oil and mineral oil were 28.4268 and 32.1794, respectively, under 1400 rpm. It was also noted that the FTP values for vegetable oil were close to those of mineral oil.

Figure 6: Flash Temperature Parameter for the Fluid Samples.


Based on the results, it can be concluded that:

  1. An inverse correlation was observed between the temperature and viscosity of the two oils (sunflower and mineral oils) that were subjected to testing. Furthermore, it has been noted that the viscosity measurements of both oil variants tend to approach each other as the temperature increases.
  2. The oil samples underwent testing at varying rotational speeds, revealing a direct correlation between the speed values and the wear scar, friction force, and coefficient of friction values.
  3. Based on the results, it can be observed that the flash temperature parameter exhibits a negative correlation with the velocity variable. Mineral oils exhibit lower wear-scar values in comparison to sunflower oil. Sunflower oil exhibits lower frictional force, flash temperature parameters, and coefficient of friction values than mineral oil.
  4. In general, the sunflower seed oil sample's thermal performance is deemed satisfactory compared to that of commercial mineral oil, thus rendering it a viable alternative to the latter



    coefficients of friction




    loads are applied by friction (N)


    applied weights (kg)


    scar diameter of wear (mm)


    Temperature Parameters for  Flash


    Pure Commercial Mineral Fluid


    Pure Sunflower Oil


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