Afton found that by optimizing automatic transmission fluids, engine lubricants and fuels, formulators have succeeded in increasing fuel economy by 6.8 percent. Globally, the impact of only 1 percent reduction in energy use saves 48 million barrels of fuel. Also, it can cut 17 billion metric tons of global carbon dioxide greenhouse gas emissions, Corless said.

He added, The theoretical limit of 7 to 10 percent fuel economy is massive, but 3 to 4 percent fuel economy increase can be achieved. These numbers have a real impact on the world from an economic and environmental perspective.

The additive maker found additional positive effects of a 1 percent fuel economy improvement on a global scale, including fuel savings of 47.6 billion barrels, 16.9 million metric ton reduction in greenhouse gas emissions, 1.7 billion saved in European carbon dioxide levies by 2020 and 29 billion annual direct consumer benefit. The Afton estimates are based on published car park mileage, fuel consumption and tailpipe emission data.

Multiple Challenges, Multiple Solutions

Vehicle design has evolved significantly in the last 15 years, Corless said. While vehicle weight and engine power have increased, fuel consumption and carbon dioxide emissions have been drastically decreasing. He noted that the average fuel consumption in passenger cars has dropped from 10 liters per 100 kilometers in 1985, to 5 L/100 km today.

These numbers are approaching the target of 56 miles per gallon by 2025 set by the United States Environment Protection Agency, according to Boris Zhmud of Applied Nano Surfaces. These results are achieved by [a multifaceted approach, including] powertrain optimization, curb weight reduction, as well as the use of low-viscosity oils and new [metal and mineral] surface coatings, he told the ACI meeting.

Applied Nano Surfaces, based in Uppsala, Sweden, develops friction and wear reduction solutions. Zhmud explained that an effective approach to improving fuel economy involves using lower viscosity oils to minimize hydrodynamic losses and lubricity additives to control wear and boundary friction.

Research by Applied Nano identified a number of approaches to reducing boundary friction and wear. However, while these techniques reduce friction, they present new challenges that must be addressed. For example, Zhmud said that highly polished or superfinished surfaces on engine components reduce operating friction; however, these operations increase manufacturing costs. In addition, superfinished surfaces exhibit poorer oil film retention and require better oil filtration to prevent damage.

Antifriction additives, while effective, can also increase formulation costs, reduce oil service interval and potentially cause yellow metal corrosion. Hard coatings, such as diamond-like carbon coating and Nikasil, protect components but increase costs. They also have poorer oil film retention, poorer thermal conductivity, are not compatible with molybdenum disulfide and can erode in service.

Finally, said Zhmud, porous coatings such as plasma transferred wire arc thermal spraying, twin wire arc spraying and Alusil can be costly. However, they provide high thermal conductivity and, therefore, efficient cooling and thicker lubricant films. They also maintain full-film lubrication.

He concluded, Triboconditioning allows users to switch to lower viscosity lubricants to improve energy efficiency without the risk of wear-related failures. Engine tests at Applied Nano showed that these coatings reduced friction mean effective pressure by up to 20 percent, which translates to 0.5 to 1.5 percent improvement in fuel efficiency.

The maximum effect is achieved in combination with low-viscosity motor oils, Zhmud explained. He contended that the use of such coatings minimizes dependence on the additive package to reduce friction, an important consideration in formulating low-SAPS (sulfated ash, phosphorus, sulfur) oils to meet ACEA C sequences.

Lubricant Solutions

Providing a historical perspective, Corless said there have been four focus areas for fuel economy over the last three decades. In the 1980s, the focus was on viscosity; namely, the use of lower viscosity oils to improve fuel efficiency. Later, we used chemistry to reduce friction during the ILSAC GF-2 and GF-3 oil specification period. Friction modifiers still have significant impact even today, he explained.

Next came ILSAC GF-5, and, according to Afton, oil formulators embarked on a quest to update old formulations to meet its requirements. This effort addressed the need to replace the chemistry that controlled high-temperature deposits because it conflicted with the chemistry needed to meet enhanced fuel economy requirements. The industry solved these problems and found a solution with the development of lubricants that both protect the engine and enhance fuel economy, Corless observed.

He labeled the present phase as technology enablement. In this environment, high-temperature deposit control is a key challenge for todays smaller but more powerful engines, according to Corless. [Effective] deposit control enables original equipment manufacturers to deliver [enhanced] fuel economy in vehicles with downsized engines. Addressing wear control and protection enables us to use ultralow viscosity oils that, in turn, enhance fuel economy, he said.

He added that fuel economy improvement is a never-ending challenge and is harder and harder to meet each year. The low-hanging fruit has already been picked, said Corless, which makes it harder to find areas for improvement.

Afton employs engine tests to evaluate friction modifier technology and aging of the lubricant and its impact on fuel economy. Corliss explained that the Afton Continuous Aging Fuel Economy Test (A-CAFE) uses any real-world driving cycle and applies to any vehicle. It measures fuel economy concurrently with drivetrain fluid aging. The test is highly precise and provides quick evaluation of the impact of a formulation change on tailpipe emissions, he said.

Another key factor in the fuel economy equation is low viscosity. Corliss stated that the yet to be established SAE 0W-16 specification provides a 1.8 to 1.7 percent fuel economy benefit just from the lower viscosity. But formulators need to be careful, he said. They need to match viscosity to the hardware because while lower viscosity may improve fuel economy, other challenges such as oxidation and wear control also must be addressed.

Low-Speed Pre-Ignition

One of the major current issues for both engine designers and oil formulators is low-speed pre-ignition (LSPI). Pre-ignition is uncontrolled combustion when the fuel/air mixture ignites before the spark plug actually sparks. When this happens, you can get massive pressure points in the cylinder that the engine is not designed to tolerate, Corless pointed out, adding that it can result in a catastrophic engine failure.

According to Aftons John Philbeam, Unfortunately, the most fuel efficient area for the engine is also the area where it is most susceptible to LSPI. As a result, car manufacturers have to tune their engines to avoid LSPI in the affected area. This is typically done by injecting more fuel than necessary, with detrimental effects on fuel economy. Therefore, he added, LSPI is a limiting factor for fuel economy and carbon dioxide reduction.

Philbeam then described a number of lubricant factors that affect LSPI. He related that one group of researchers evaluated different base stocks in a prototype engine. They found that higher API Group numbers correlated with lower LSPI frequency.

In addition, higher calcium levels correlate with higher LSPI frequency, while increasing phosphorous and molybdenum levels decreased the frequency. The research found no clear correlation between either lubricant volatility or oxidative characteristics and LSPI frequency.

There is no single solution for LSPI, according to Corless. The solution should be a combination of efforts from all key stakeholders to eliminate the problem. Our company has designed a bench engine test that mimics LSPI. By measuring its relative frequency, we are trying to formulate an oil that can achieve low LSPI frequency, he observed.

The Big Picture

Corless went on to say that the oil not only improves fuel economy, but it also protects the engine and enables automakers to bring the latest engine technology to market while delivering higher performance. The question now is not about the lubricant itself, but about what the lubricant can do to enable OEMs to deploy new hardware that offers gradual changes in fuel economy.

Downsized engines, gasoline direct injection and turbocharging all present challenges for the lubricant formulator, Corless said. Lubricant formulators need to address the multiple issues caused by the pressures, geometries, fuel strategies and combustion control used in modern engines. They need to have a better understanding of what the OEMs are doing and where the engine designers want to take things, he noted.

Taking into consideration how the overall system works, fuel economy can be much higher than it is today, according to Afton. For example, optimized automatic transmission fluid gives 2.1 percent fuel economy improvement. If you add to the hardware optimized engine oil, the fuel economy improvement soars to 5.2 percent, and by adding this to hardware and optimized fuel, the fuel economy improvement peaks at 6.8 percent, Corless said.

Finally, he added, a great pass in one qualification test is almost meaningless if the same fluid cannot meet the other specification requirements. Finding the best solution requires a holistic approach. The key question is, How does the total solution add value? he said. The future development of fuel economy oils will be based on evaluations more aligned with actual use.

Corless reduced this philosophy to a simple observation. A holistic approach is characterized by the belief that the parts of something are intimately interconnected and explicable only by reference to the whole. It is the key in unlocking the true value of our task.