SCHOLARSHIP RESEARCH

The Effect of High Viscosity Index on Fuel Economy with Bio-Derived Hydraulic Oils

Chris Jaudon*, Robert Jackson* and Tom Gallagher+*Department of Mechanical Engineering and +Department of Forestry and Wildlife Sciences

Auburn University, Auburn, Ala.

Editor’s Note: This month TLT profiles the 2015 recipient of The E. Richard Booser Scholarship Award, Chris Jaudon (Auburn University). The Booser scholarship is awarded annually to undergraduate students who have an interest in pursuing a career in tribology. As a requirement for receiving an STLE scholarship, students are given the opportunity to participate in a tribology research project and to submit a report summarizing their research. For more information about the Booser scholarship, visit www.stle.org.

Chris Jaudon is a junior at Auburn University in chemical engineering also pursuing a tribology minor. The Booser scholarship has allowed him to conduct his research in Dr. Robert Jackson’s Mechanical Engi-neering Tribology Lab. Jaudon is president of Auburn’s Tribology and Lubrication Sciences student organization. He also enjoys volunteering his time coaching youth sports in the Auburn community. Jaudon plans to graduate in May 2017. You can reach him at ctj0008@auburn.edu.

INTRODUCTIONRenewable, biodegradable fluids that can keep up with the increasing de-mands of friction efficiency and wear protection that are required in the lu-bricants industry are becoming more highly sought after. Marine and for-estry applications help drive this de-mand because they can be particularly sensitive to the dangers of mineral oil lubricant spills. This study aims to compare new high viscosity index bio-derived hydraulic fluids to more traditional hydraulic oils on the basis of lubricity and wear protection. Fluids that have lower viscosity at cool start up temperatures, but can maintain that viscosity to achieve volumetric efficiency and wear protection at high temperatures improve efficiency in hy-draulic systems.1 High viscosity index (VI) fluids are beneficial in lubricating hydraulic systems because they are able to maintain their viscosity at high op-erating temperatures. Recent studies have shown that very high VI fluids can improve film formation and friction characteristics.2 To investigate these

benefits this study utilizes ball-on-disk friction tests as well as a fuel economy field study using the most recent model of a popular industry skidder. The skid-der is used in the forestry and logging industry to transport freshly cut logs to a central location. The combination of lab and field measurements allows for an accurate evaluation of the possi-bilities of fully formulated bio-derived lubricants.

MATERIALS AND METHODSThe hydraulic fluids studied were bio-derived ISO 46 base oils with viscosity indexes of 223, 204 and 147. These were tested against the manufacturer’s recommended petroleum based oil, an SAE 10 oil with a VI of 114. A Bruk-er-UMT friction testing machine was utilized to perform a ball-on-disk test (see Figure 1). A steel ball was on an E52100 steel disk. For Stribeck curve testing, coefficient of friction data was collected for a constant load of 30 N and rotational speeds ranging from 1-400 rpm. The disc was unloaded and then reloaded with a constant force of

80 N and a rotational speed of 0.1 m/s for two hours. In order to check re-peatability, each test case was repeated three times.

This test was also repeated twice at 100°C, but with new fluid and ball and disk samples. A heat lamp that operat-ed on a temperature control maintained the temperature. A Bruker Dektak150 stylus profilometer was used to mea-

Figure 1 | Bruker UMT used to perform ball-on-disk test.

20 The color of molten sulfur is: yellow, red, blue or silvery white. A.

sure the wear on the surface of each disk (see Figure 2).

The field test portion was performed using a forestry skidder that featured the most recent technology in that area. Each hydraulic fluid was tested eight times with each run consisting of 10 approximately half mile laps. The runs alternated loaded and unloaded laps to simulate typical logging operation. The logs were used consistently throughout each test and to ensure repeatability even though weight was lost from bark and water, the standard was tested at the beginning and end of the runs. Af-ter each of the eight tests the fuel con-sumption was recorded.

RESULTS AND DISCUSSIONThe results of the friction test shown in Figure 3 indicate the bio-derived fluids are able to outperform or match the friction performance of the tradi-tionally engineered product at room temperature. When the temperature is increased to 100°C the friction slightly increases in the standard oil while the high VI fluids are able to improve fric-tion performance. At high temperatures the bio fluids maintain more of their viscosity while it is possible the stan-dard oil viscosity falls below its optimal operating range.

Figures 4 and 5 show the wear widths and depths that were measured

Figure 2 | Bruker Dektak 150 stylus used to measure disk surfaces.

Figure 3 | Average coefficient of friction at 80 N load and 0.1 m/s.

Figure 4 | Average wear track width in micrometers.

Figure 5 | Average wear track depth in micrometers.

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after the ball-on-disk test. Bio fluids 1 and 3 fail to achieve the same wear protection as the standard oil in the room tem-perature test, but bio fluid 3 in particular is able to provide superior wear protection when the temperature rises to 100°C (see Figure 6). One possible mechanism for this is the extreme pressure additives inside the bio fluid are only activated at the high temperatures sometimes encountered in the operating ranges for hydraulic systems.

Figure 7 shows the average fuel consumption, while Fig-ure 8 presents GPS data that shows the course on which the skidder pulled the logs (see Figures 9 and 10). The results of the fuel consumption study are very consistent. Little or no change in fuel economy occurred when switching between the different hydraulic oils. There are two possible conclusions to be drawn from these results. The first is that the viscosity in-dex of hydraulic oils does not have an effect on fuel economy. This conclusion is most likely premature and a more accurate

Figure 6 | Plotted wear scar data measured by the profilometer for Bio 1.

Figure 7 | Fuel economy average consumption in gallons per minute.

Figure 8 | Aerial view of skidder course.

Figure 9 | Skidder lowering logs after loaded lap.

Figure 10 | Skidder pulling logs.

22 The color that white phosphorus glows when oxidizing is: purple, blue, white or green. A.

conclusion would be that fuel economy is not affected by viscosity index in the skidder specifically. The majority of the skidder’s hydraulic system engage-ment occurs from the operation of the grapple during the raising and lower-ing of the logs, which accounts for a small portion of the fuel consumption (see Figure 11). Other equipment that is more hydraulically driven than the skidder could still see a difference.

CONCLUSIONOverall, this study shows that bio-derived lubricant technology is on par with and has the potential to surpass their traditional counterparts. High VI fluids appear equipped to achieve low friction and wear at operating temper-atures. While long-term wear perfor-mance needs to be further investigated, from a fuel economy perspective the bio-derived hydraulic oils can be used interchangeably with the petroleum

product. The key is that these new fluids simultaneously provide a more environmentally responsible option. The combination of environmental and tribological benefits warrants more use and investigation of these bio-derived fluids.

Figure 11 | Chris Jaudon operating the skidder.

REFERENCES

1. Herzog, S., Placek, D., Simko, R. and Neveu, C. (2002), “Predicting the pump efficiency of hydraulic fluids to maximize system per-formance,” SAE Technical Paper 2002-01-1430, DOI:10.4271/2002-01-1430.

2. Dardin, A., Hedrich, K., Mül-ler, M., Topolovec-Miklozic, K. et al. (2003), “Influence of polyal-kylmethacrylate viscosity index improvers on the efficiency of lubricants,” SAE Technical Paper 2003-01-1967, DOI:10.4271/2003-01-1967.

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