Assessing Energy Efficiency Benefits of Synthetics—Part 1

 10th Apr 2015

Synthetic lubricants can be used to help improve energy efficiency in operations, but do you understand why? Did you realize that not all synthetic lubricants can deliver the same benefits?  In controlled testing, both in the lab and in the field, assessed the energy efficiency benefits of three synthetic oils, formulated from varied base oils.

Tests determined that Polyalphaolefin (PAO, API Group IV)- synthetic based gear oils delivered superior efficiency benefits, showing an average of 6 percent efficiency over API Group III/polyisobutylene (PIB)-based gear oil.  Further testing showed gear oils containing PIB resulted in significant shear loss, as compared to PAO-only based gear oil, which resulted in high rates of wear and diminished equipment life.

To illustrate the potential efficiency benefits that can be achieved by converting to a synthetic product, a number of controlled tests were carried out, in which the energy efficiency benefits of synthetic lubricants as compared to those of mineral based lubricants were assessed.

As background, conducting an experiment to measure the energy efficiency benefits of finished lubricants is inherently challenging.  In one experiment, a Mini Traction machine (MTM) was used to measure and compare the traction forces transmitted across a lubricant film under varied amounts of sliding, while controlling load, speed and temperature.

Lubs article

                                          MTM Traction Plots - Mineral vs. Synthetic

The results illustrated that traction coefficient measurement for synthetic lubricants over a range of slide to roll ratios was much lower than typical mineral oil based products, which results in a reduction in heat generation and lower overall system operating temperatures.

Reduced heat generation and lower temperature operation can translate to improved energy efficiency in system operation.

In addition the lubricants were tested using a conventional elastohydrodynamic lubrication (EHL) ball on disc rig, equipped with temperature mapping using infrared imaging to assess heat within the system. Essentially, this process creates a map of the lubricated contact area under highly loaded EHL conditions, with varying amounts of sliding¯controlling load, speed and inlet temperature.

At a given sliding speed, fluids with lower shear stress will provide lower temperature rise across the EHL contact. Tests revealed a variation in temperature as shearing of the fluid in the contact zone caused the disc surface to heat. This increase in temperature is a function of the heat generation per unit area, a product of the fluid shear stress under the contact conditions and sliding speed.

The performance of advanced synthetic lubricants was assessed against conventional mineral oil based lubricants, and determined that synthetic lubricants reduced the temperature in the contact zone by more than 4°C (39.2°F).

lubes article 2

In the next phase of testing, a Modular Small Worm Gear (MSWG) test rig was used to assess torque.  Torque was investigated, rather than current, as current/voltage measurements have much higher associated error.  The MSWG in this test employed two torque meters to measure torque into and out of the gearbox and, to assess percent efficiency, output torque was divided by input torque.

lubes article 3

As the image above illustrates, the gearbox operating with synthetic fluid - which ran at full speed (1800 rpm input), at 100 percent rated load at 20/1 reduction ration -  indicated a statistically validated energy efficiency improvement of 3 percent, as compared to the conventional gear oil.

So, as you can see from these lab tests, choosing an advanced synthetic lubricant can have a dramatic impact on the efficiency of gearbox operations. 

"Assessing Energy Efficiency Benefits of Synthetics¯Part 1" by Angela Galiano-Roth used with permission of the Mobil SHCTM Club (all rights reserved.)

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