All of these changes have created big challenges for the oils that lubricate these engines, and meeting them has required a multi-pronged attack. Thomas Hickl, of German automaker Adam Opel AG, recounted how far engines have come during a presentation at UNITIs Mineral Oil Technology Congress in April and recounted the resulting developments of passenger car engine oil specifications. Todays engine oils provide the protection needed to ensure long-term engine durability, long oil change intervals, compliance with emissions regulations and improved fuel economy, while at the same time meeting the challenges posed by a proliferation of fuel types and qualities.

But these accomplishments have not been easy, Hickl said, and the lubricants industry will face more challenges at least into the near future as the trends in engine evolution look likely to continue.

Smaller and More Powerful

The most important developments affecting engine oils have been the simultaneous increase in engine power and reduction of engine size. Hickl cited some examples which he said have been typical of the industry. The Volkswagen Golf had a maximum output of 66 horsepower in 1996, he said, and that number rose 79 percent to 118 hp by 2010. Over the same time span, however, the size of the oil sump decreased from 3.8 liters to 3.6 liters.

The predecessor of Opels Astra, the Kadett, was capable of 55 hp in 1991, Hickl said, compared to 132 hp for the 2010 Astra – an increase of 140 percent. The Astras oil volume did increase, but by a much smaller proportion – from 3.5 liters to 4.5 liters.

Increasing power output while reducing engine size creates a double whammy on power density.

Power density has increased remarkably over time, Hickl said, which stresses the oil by increasing temperatures.

The Golfs power density more than doubled from 1996 to 2010, rising from 37 kilowatts per liter to 85 kW/l. The Kadett/Astra underwent a similar change, as its power density rose 140 percent from 1991 to 2010. Higher power density increases the internal mechanical pressure on engine components, raising the challenge for oils tasked with lubricating them. Increased density also raises the peak temperatures to which oils are exposed, something that tends to speed oxidation and formation of deposits.

By themselves, these changes would require oils to have better resistance to oxidation and better deposit control. But the challenge has been compounded, Hickl noted, by a push to make oils last longer. From 1996 to 2010, Volkswagen doubled the recommended drain interval for the Golf, from 15,000 kilometers or one year to 30,000 km or two years. The interval for the Kadett/Astra increased even more – from 5,000 km or six months in 1991 to 30,000 km or 12 months in 2010.

As Hickl noted, automakers have been adding engine components meant to boost power output and improve fuel economy. Modern gasoline engines increasingly use direct injection, variable cam shaft phasing, and optimized turbocharger and compressor arrangements. Diesel engines use similar technologies, including two-stage turbochargers. Modern diesel engines also rely on complex after-treatment systems, including catalysts and particulate filters, to comply with the latest regulations.

All of these added components affect the life and durability of engine oils.

For example, direct injection creates more hydrocarbon particles in the blow-by gas, and this must be neutralized and suspended by the oil. Supercharging increases the temperature at the piston rings, creates high bearing loads and increases peak oil temperature, oil consumption and blow-by gas volume.

The design of the combustion chamber and pistons can also increase peak temperatures, oil consumption and blow-by gas volume. Exhaust gas recirculation systems create carbon particles, aldehydes and radicals – all of which must be neutralized by the oil.

A final factor affecting oil formulation in Europe is the proliferation of fuel types. Among those now on the market in Europe are compressed natural gas, liquefied petroleum gas and diesel with bio fuels. The latter is conventional diesel supplemented with biofuels that may come from a number of different plant oils. Moreover, the proportion of bio content can range from 7 percent up to 100 percent.

In 1991, Hickl said, OEMs had to design engines to be compatible with only four types of fuels. Today, they must contend with the potential use of gasoline, various grades of ethanol, compressed natural gas, liquefied petroleum gas and conventional diesel. The latter currently contains 7 percent bio-fuel, although the European Union is considering raising the minimum portion of reusable content to 10 percent. But diesel fuels containing varying percentages of fatty acid methyl esters – up to 100 percent – can also be found on the market. Each fuel influences engine combustion behavior and oil aging and degradation in different ways, Hickl said.

ACEA Faces the Challenge

Ensuring that engine oils address all of these issues has been a difficult task and has involved a long list of organizations and companies. In Europe, the European Automobile Manufacturers Association (ACEA) develops specifications in cooperation with the oil and additive industries. Across the Atlantic, U.S. automakers acting as the International Lubricant Standardization and Approval Committee (ILSAC) follow a similar model to develop specifications used in that region and other parts of the world. ACEA maintains light-duty test standards with requirements for passenger cars powered by both gasoline and diesel. ACEA Sequences A and B allow higher levels of sulphated ash, phosphorus and sulphur, while Sequence C sets stricter limits on SAPS in order to prevent damage to emissions control components.

ACEAs specs are overseen by a fuels and lubes subgroup that meets four times per year and holds monthly teleconferences to discuss issues. In addition to developing standards to cover the needs of current and future engines and, it also works to ensure backward compatibility with older engines. The subgroup also considers environmental and regulatory requirements, Hickl said, always searching to develop sequences to cover the needs in Europe as well as other regions.

The sequences consist of tests that focus on various performance needs such as high-temperature deposits, sludge, wear and fuel economy. In addition, diesel engine oil sequences include tests for medium-temperature dispersivity, piston cleanliness, ring sticking and wear and oil consumption.

OEMs Up the Ante

As Hickl explained, the oil quality specified by ACEA sequences forms the basis of requirements set by individual automakers for their own engines. To these requirements, OEMs are increasingly adding other, more demanding operating characteristics that define in-house specifications. Examples include:

Daimler Benz MB 229.x, a low-ash specification

based on ACEA C sequences;

Volkswagen 501 0x to 507 0x specifications that include three different quality levels: a basic oil level based on ACEA A3/B3; a medium standard based on ACEA A3/B4; and a high standard based on ACEA C3 for long drain intervals and low ash to protect diesel particulate filters; GMs Dexos1 and Dexos2, based on selected ACEA, API and ILSAC tests with partially increased limits.

OEMs formulate additional specifications beyond ACEA, API, and ILSAC for a number of reasons. First, they may need to meet specific maintenance requirements such as extended drain intervals. Also, specific engine designs such as direct injection and turbocharging can lead to requirements exceeding those provided by ACEA approved oils. OEM specific fuel adaptations such as LNG, CNG, and biofuels may require special oil characteristics. Lastly, brand specific strategic alliances such as a need for global oil availability can lead to OEM-specific requirements.

ACEA Prepares for the Future

Today, Hickl said, ACEA is facing a number of challenges beyond those posed by keeping abreast of the needs of modern engines. For example, the M111 sludge test has expired because the engine on which it runs is no longer available and has been replaced on an interim basis by the M271 sludge test. A permanent replacement has yet to be identified.

ACEAs 2010 sequences include so-called distinction features to separate the A and B sequences from the C sequences by adding a minimum sulphated ash requirement for A3/B3 and A4/B4. It also increases the fresh oil total base number limit as well as the after-test TBN for the turbocharged direct injection test, making the base Sequence A and B oils more robust to accommodate high-sulphur fuels in non-European markets. This makes the A/B oils a clear product choice in these markets rather than C sequence oils. The 2010 sequences also drop the phosphorus limit of ACEA C3.

The major concern in developing new and successor tests is ensuring the engines chosen have sufficient life expectancy to make it worth investing time and money in test development, Hickl said. Another problem is that newer engines are equipped with sophisticated control units and antitheft devices that inhibit the ability of test labs to fully understand and characterize engine behavior, further delaying test development.

The most important effort for ACEA today is the development of several new tests to determine the effects of biodiesel and cold start pumpability, and a successor to the Daimler Benz 4 dispersivity test. The organization is also developing a registration system for ACEA claims. Most recently, ACEA began discussions with API and ILSAC on the joint development of engine tests. This will help reduce test development costs and help each organization achieve common goals.