Designing Oil for Small Hot Engines


Small and powerful, new turbocharged gasoline direct-injection engines improve fuel economy and lower CO2 emissions, but they present significant challenges for lubrication.

TGDI engines currently account for 15 to 20 percent of new engine production, and in three to four years, their share will double in Europe, Keith Howard, technical manager with Lubrizols Engine Oils Group, told the ICIS Asian Base Oils & Lubricants Conference in Singapore in June.

TGDI penetration is moving very fast, Howard said, and automakers are increasingly protecting their technologies with in-house engine oil specification tests.

Gasoline direct injection involves injection of the gasoline directly into the combustion chamber, rather than into the intake port, providing power and efficiency benefits, Howard explained. Adding a turbocharger further increases power and efficiency, but also puts significant stress on the engine oil.

Tests show the TGDI engine providing a 24 percent reduction in fuel consumption, 30 percent reduction in engine capacity and 25 percent improvement in CO2 emissions, compared to a port fuel injection engine, the Derbyshire, U.K., based manager said. The TGDI engine is enabling European automakers to meet Europes strict CO2 limits and avoid punishing penalties.

In addition, TGDI engines offer performance and drivability benefits, providing the responsiveness of a bigger engine. Virtually every automaker in Europe and North America, Howard said, has embraced or at least introduced the TDGI engine. Domestic Chinese automakers are following fast with their own TGDI technologies.

The key challenges for engine oil in the turbocharged gasoline direct-injection engine are:

– Oil oxidation leading to thickening, sludge and deposits;
– Increased particulates;
– Increased bearing loads; and
– Low speed pre-ignition.

Poor quality fuels and stop-start driving conditions increase the severity of operation.

Lubrizols research on TGDI engines has focused on oxidation, thickening and sludge deposits, Howard continued. The company has developed a TGDI engine oxidation and sludge test at its Hazelwood, U.K. laboratory, and conducted field tests in China to confirm the lab results.

Lubrizol found the TGDI engine was much more severe on the engine oil compared to a port fuel injection engine of equivalent power. Using the same fuel and oil, the oil in the TGDI engine tests failed at 160 hours, compared to 240 hours in the port fuel injection engine.

Consistently, Lubrizol found that with low tier oil (API SG level) in the TGDI engine, high temperature oxidation caused viscosity increases and sludge deposits, filter blockage and turbocharger deposits. By contrast, high tier oil (ACEA A3/B4 level plus added performance chemistry for use in developing markets where fuel quality is low) protected the engine.

A 10,000 kilometer field trial in China confirmed that issues seen on the engine dynamometer occurred in the real world, and allowed Lubrizol to assess the effects of local, poor quality fuel. The results correlated, and the low tier oil couldnt go 10,000 km, Howard said. The engine test demonstrated that oil quality is critical with the TGDI engine.

More and more, he continued, OEMs are seeing the need to have specific requirements in the form of their own [engine oil] specifications. Technologies are diverse, and each needs its own specs.

Good quality base oil is the foundation. There is much focus on [API] Group III base oils, as they combine very good oxidation stability with other properties and are very cost effective compared to Group IV PAOs.

Howard highlighted the additive solutions for some of the TGDI challenges. For sludge and deposit protection, you need antioxidants, detergents and dispersants. For fuel dilution, you need the right viscosity, antioxidants, and detergents. For lower quality gasoline, you need antioxidants and detergents. For higher soot levels, you need antiwear additives and dispersants.

OEMs are protecting their TGDI engines by bringing these engine types into industry-wide specification tests, bringing their specific TGDI engines into in-house specification tests, and developing higher performance specs for developing markets, Howard concluded.

And, he added, no OEM will reduce drain intervals with these engines.

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