John Smythe, global marine and large engine technical adviser at Infineum, discusses the growing use of Group II, as well as the challenges and benefits that this shift could bring to marine and gas applications.

Trends in automotive crankcase lubricant formulations, which account for over half of the base stock utilisation, are impacting the supply and demand balance of base stocks globally. As this sector looks to improve fuel economy and reduce emissions, the use of high quality Group II and III base stocks is growing quickly. The inability of Group I products to deliver the right characteristics for automotive applications has resulted in a number of capacity reductions and plant closures in Europe, which have reduced supply by more than one million tonnes.

Over the same period, there has been a significant increase in the availability of Group II base stocks as new plants and capacity additions have come on stream. This has driven down the cost, making Group II base stocks increasingly attractive. With further capacity additions scheduled over the next two to three years, a shift to these higher quality products in both gas engine and marine applications seems fairly inevitable.

Group II benefits and challenges in marine

Group II base stocks have a number of benefits over their Group I counterparts when formulating trunk piston engine oils (TPEO) for medium-speed, four-stroke engines. These include:

• Better oxidation control
• Improved NOACK stability
• Enhanced viscosity control

However, using Group II to develop TPEO also presents lubricant formulation challenges, particularly concerning asphaltene-handling capabilities.

Most of the ships that use TPEO run on heavy fuel oil, which contains large polyaromatic species known as asphaltenes. During engine operation, these species can migrate into the engine oil via fuel contamination. Here they can agglomerate to form black sludge, which leads to high levels of deposit formation and results in piston deposits, choked oil galleries and oil starvation. Deposits on the piston undercrown are of particular concern because they act as insulation, preventing the lubricant from effectively transferring heat away from the piston, which can lead to hot corrosion of the piston crown.

Oils formulated with Group I base oils with salicylate technology have demonstrated excellent performance over many years of field operation. Not only do they offer excellent asphaltene handling capabilities, but also excellent engine protection, oil life and reduced operating costs. But the picture is very different when Group II base stocks are used. Their lower solvency means conventional additives are less able to handle asphaltenes, and a new additive system is required to ensure TPEO formulated in these high quality base stocks deliver the required level of engine cleanliness.

Group II in gas engine oils

Until recently, Group I base stocks have been the basis of most stationary gas engine oil formulations. But again, the demand for higher performance lubricants from engine manufacturers means this picture is changing.

Group II base oils offer performance improvements in most aspects of lubricant testing. The improved oxidation control they can deliver is of particular interest in the latest high efficiency engines. These advantages mean that we are seeing some OEMs, including MTU, MWM Waukesha and Rolls Royce, starting to request Group II only formulations.