Now a European automaker contends that the industry needs to update how it defines and dif-ferentiates between base stocks. According to PSA Peugeot Citroen, meeting future emissions regula-tions will require that base oil marketers and lube formulators have information on a number of ad-ditional parameters – such as temporary viscos-ity loss, bio-fuel retention and friction properties under different conditions. Speaking at a February conference, officials said that having such informa-tion will help formulators choose base stocks that will help meet performance demands.

Powertrain oils are facing great challenges, Technical Manager for Automotive Lubricants Sebastien Vautier told the ICIS World Base Oils and Lubricants Conference in London. Breakthroughs are needed not only on [fin-ished lubricant] formulations; base oils must contribute.

Existing definitions for API base oil catego-ries are relatively simple. Group I oils are those that contain less than 90 percent saturates and/ or more than 0.03 percent sulfur and which have viscosity index of at least 80 but less than 120. Group II and III both have more than 90 percent saturates and less than 0.03 percent sulfur. The difference is that Group II oils have viscosity indices between 80 and 119, while Group IIIs have VI of at least 120. Group IV is devoted to polyalphaolefins, and Group V is a catch-all for all other base stocks.

The definitions for Groups I, II and III have been useful in helping define base oil perfor-mance in automotive engine oils and transmis-sion fluids. Saturates aid oxidative stability, so formulators needed high levels to help meet expectations for longer drain intervals. They also wanted oils that were not as thick at low temperatures, in order to reduce friction and improve fuel economy, but in order to protect components from wear they needed the oil to not thin too much at higher temperatures. Vis-cosity index – the ability of an oil to maintain viscosity as temperature changes – addressed these concerns. Finally, sulfur levels were very relevant for reducing sulfur oxide emissions and later to protect vehicle emissions control devices.

Demands on engine oils continue to rise, however, placing more exacting requirements on base oils, additives and formulation, said Vautier and Cyril Bastian, a PSA technical liaison for lubricants, who co-presented with Vautier. They noted that the main concern go-ing forward will be the focus on improving fuel economy as a means of reducing both operat-ing costs and carbon dioxide emissions.

Bastian said the CO2 emissions mandates lying ahead are ambitious.

Generally speaking, the CO2 race is speed-ing up for PSA, he said. The steps [between sequential emissions targets] are getting smaller and smaller but the costs higher and the constraints tougher.

One cost, he said, will be that Group II oils and many Group III oils will no longer provide the low levels of volatility demanded in oils of low viscosity. Volatility is already limiting the use of conventional oils and, if we want to continue decreasing oil viscosity, we have for the moment no other choice than switching to Group III+, IV or V base oils.

Base stock marketers already have sev-eral ways of measuring the viscosity of their products – kinematic viscosity, cold-cranking viscosity, pumping viscosity and high-tempera-ture high-shear viscosity. Peugeot believes it is becoming important to have additional infor-mation about viscosity – specifically the degree to which viscosity changes during engine op-eration. Vautier said that while both temporary and permanent viscosity loss occurs, higher levels of temporary loss appear to improve fuel economy. Components such as viscosity index improvers and certain chemical additives affect temporary viscosity loss, but base oils are also a factor, and the effect can vary from oil to oil, Vautier said.

We anticipate the evaluation criteria of an oil to be moving from kinematic viscosity and high-temperature high-shear to the full rheological behavior, he said, going on to cite results of tests conducted with Total on engine oil samples that were identical except for their base stock. One of the finished oils had a higher temporary loss of viscosity during the test. The oil which is giving the best full economy … is not the one with higher permanent viscosity loss, but the one with higher temporary viscosity loss.

Peugeot also wants information about the tribological behavior of different base oils, that is, the friction experienced by lubricated compo-nents under certain conditions. Vau-tier cited tests that Peugeot conduct-ed with a Cameron-Plint tribometer on five engine oil samples, the only difference being the base stock con-tained in each. Researchers recorded the coefficient of friction of each oil at three different temperatures. At the lowest temperature, results for all oils were practically identical. At the middle temperature, three of the oils recorded significantly better results than the other two. At the higest tem-perature, one of the three attained significantly better results than the other four, which were close to the same as each other.

Vautier said friction is becoming a bigger concern as the auto industry trends toward lighter engine oils in its effort to improve fuel economy. He predicted that base oil market-ers will start providing information about frictional properties based on tests conducted with new apparatus-es such as a High Frequency Recip-rocating Rig and a Mini-Traction-Machine.

Its well known that decreasing viscosity is increasing the risks of unacceptable wear or seizure, he said. We now have a lot of wonder-ful tools to evaluate at early steps the influence of such changes and understand mechanisms of sliding/ rolling conditions. They need to be used extensively as screeners for future technologies.

Base oil suppliers should also begin to measure the effects that their prod-ucts have on bio-fuel retention of a finished engine oil in the oil sump, Vautier said. Bio-fuels have become a big concern the past couple years due to the discovery that they tend to accumulate in oil sumps, unlike con-ventional fuel. Working once again with Total, Peugeot found that differ-ent base oils have different effects on the rate at which bio-fuels evaporate in the sump.

Engine oils are subject to fuel di-lution and dilution rates will increase in the future for many reasons, Vau-tier said. Fuel evaporation patterns of different base oils can be different with time, with temperature, and de-pending on the fuel type. We believe that, in the near future, formulators will need such information in the basic data package for base oils.

Vautier and Bastian said formulators also need more information about base stock compatibility with engine materials. In some cases this results from changes in the base stocks that are used.

With the increasing use of unconventional oils – polyalphaolefin and Group V fluids – we are facing new issues, Vautier said. One of them is the compatibility of polyacrylic materials, which are the major elastomer type being used on engines and gearboxes for static and dynamic sealing applications. Base oil marketers also need to keep up with new materials introduced as en-gines evolve, he stressed.

Oil formulations are changing, but automotive com-ponents are also changing, and the interactions between base oils and recent innovations – like diamond-like coatings or polymer coatings – need to be evaluated, he said.

Vautier and Bastian expect that at least some of the parameters on their list will be added to the product in-formation that base oil marketers provide. But they also urged industry to revise its base oil definitions in order to make them more precise. The differences in some qualities have become too great for the categories to remain meaningful, Vautier said. He expressed particular concern about the implications for base oil interchange guidelines – the industrys rules about when lubricant blenders may substitute base stocks without resubmitting to expensive specification qualification programs.

The range of qualities is especially large for Group III oils, he said. To illustrate the problem, he noted that switching among Group IIIs in some formulations can cause huge swings in an engine oils kinematic viscosity – even if the Group III constitutes just 10 percent of the base stock.

Do Groups III, IV and V need to be redefined? he asked. The industry is continually moving to higher quality base oils, and we think we will need the catego-ries to be very precisely defined in order to allow base oil interchange and to help reduce development costs.

The Peugeot representatives acknowledged that so far they have noticed no efforts in the industry to undertake the things they are advocating.

Not really, but if the Group III+ subgroup has been unofficially created within the industry, its because it has superior properties that Group III doesnt define clearly enough, Vautier said.

Still, he expressed optimism that change can occur. Everyone is going to have to start monitoring these properties, he said. If there can be some cooperation on defining categories it will help all of us.