Courtesy of Engine Technology International
AS THE DRIVE TO REDUCE GHGs AND INCREASE FUEL EFFICIENCY CONTINUES TO ACCELERATE, LOWER ‘HIGH TEMPERATURE HIGH SHEAR’ A measure of a fluid's resistance to flow. A fluid with a higher viscosity flows less easily. ENGINE OIL IS PLAYING AN EVER-IMPORTANT ROLE.
Reduced Mobile sources - Pollutant exhaust gases created by the combustion of fuel. Water and CO2 are not included in this category, but CO, NOx, and hydrocarbons are and are thus subject to legislative control. All three are emitted by gasoline engines, while diesel engines also emit particulates that are regulated. Stationary sources - The release of sulfur oxides and particulates from power stations that can be influenced by fuel composition. Local authorities control the sulfur content of heavy fuel oils used in such applications. and increased fuel economy continues to force changes in engine hardware design across the world. Changes in heavy-duty diesel engine technology and operating conditions have resulted in engine downsizing, downspeeding, higher oil temperatures and start/stop technology to name a few. At the same time, advances in heavy-duty diesel engine oils have played a vital role in enabling these improvements.
It is generally accepted that utilizing lower viscosity grades – moving from SAE 15W-40 to 10W-30 and 5W-30 viscosity grades – delivers increased fuel economy and reduced GHG. Meanwhile, it has been proved through stringent testing that hardware protection is not sacrificed.
A typical method of measuring the viscosity of an engine lubricant is The measurement of a fluid's resistance to flow under the force of gravity at a specific temperature, usually 40°C or 100°C. (KV) – the time taken for a fixed volume of oil to flow through a tube under the force of gravity. However, in an operating engine, oil is exposed to more than just gravity, notably where it has to run in hotter and more severe operating conditions. The lubricant is required to lubricate and protect areas such as the bearings and the camshaft, as well as the piston rings and liners, under high shear conditions at high operating temperatures.
High-temperature, high-shear (High Temperature High Shear. A measure of a fluid’s resistance to flow under conditions resembling highly-loaded journal bearings in fired internal combustion engines, typically 1 million s–1 at 150°C.) dynamic viscosity is the current industry standard that
best predicts fluid behavior in these more representative operating conditions. HTHS measures the temporary viscosity loss of an engine oil under high shear at elevated temperatures. The number measures the resistance to flow of the oil, simulating the narrow tolerances and high speeds between moving parts in a
hot engine. As the HTHS viscosity reduces, the predicted fuel efficiency increases. It is imperative to ensure that oils do not shear down at high temperatures and shear rates, ensuring the film strength remains acceptable for component longevity at all times during the oil drain interval.
Traditionally heavy-duty diesel engine oils have had minimum HTHS viscosity rates of 3.5 mPa·s – also commonly referred to as centipoise (cP). Lower HTHS viscosity is actively being pursued by an increasing number of heavy-duty OEMs, enabling efficiency improvements in engine technology as well as directly delivering the fuel-efficiency benefits that properly formulated lower viscosity oils can provide. This focus covers both factory fill applications for new and future engine designs and considers the use of low HTHS viscosity oils in specified engines dating back several years.
Industry specifications are also being rolled out to reflect the needs of engine manufacturers. The API. The primary oil and natural gas trade association in the United States. API operates a voluntary licensing and certification program that allows engine oil marketers to use the API Engine Oil Quality Marks if their products meet specific requirements. (American Petroleum Institute. The primary oil and natural gas trade association in the United States. API operates a voluntary licensing and certification program that allows engine oil marketers to use the API Engine Oil Quality Marks if their products meet specific requirements.) saw first licensing of its first split category of API CK-4 and API FA-4 in December 2016, with new API FA-4 oils offering fuel efficiency benefits through lower HTHS viscosities between 3.2 cP and 2.9 cP. The European Automobile Manufacturers’ Association (European Automobile Manufacturers Association (Association des Constructeurs Européens d'Automobiles). The primary automotive standards organization in the European Union, ACEA defines performance specifications for automotive lubricants.) is likely to follow with a new sequence at similar HTHS viscosity rates in the next upgrade following the recently updated ACEA 2016 Oil Sequences.
Keith Corkwell, global business manager for Lubrizol’s heavy-duty diesel engine additives segment, comments, “The move to low HTHS heavy-duty engine oils presents opportunities and challenges. In order to assure continued durability and protection under reduced high-temperature, high-shear environments, new additive technology is essential to enable the move to low HTHS engine lubricants. When moving to low HTHS viscosity solutions, the additive and performance polymer have a more significant role to play in the overall finished oil formulation.
“Lubrizol has many years of proven experience in developing and commercializing low HTHS technology. In heavy-duty diesel engines, this includes the North American introduction of the new low HTHS category API FA-4. With over 80,000,000 km of real world driving (and still counting), Lubrizol has developed the knowledge and know-how in moving to low HTHS solutions and is ready to engage with its partners to exploit the full benefits and opportunities low HTHS heavy-duty diesel lubricants have to offer, both today and in the years to come.”