LUBRICANTS CHALLENGES FACED BY OUR ENGINEERS

Under constant scrutiny to improve fuel economy and emissions output, while also having to raise the performance bar, car makers are increasingly turning to lubricant suppliers to help them gain an advantage in new engine developments.

Euro 6 legislation has challenged powertrain engineers around the world to bring down emissions from passenger car engines to levels not thought possible just 20 years ago. Through the use of efficient filters, forced induction and advanced engine management systems – to name just three technologies – and a willingness to downsize displacement capacity, NO_x and PM have been reduced dramatically, but now the attention turns back to CO₂, and how best to further drive down harmful tailpipe pollutants and improve fuel economy, while continuing to set a new bar when it comes to power and performance.

Total’s lubricants department is one such R&D hub that’s working hard to realize this trio of not-so-low hanging fruits. From its research centre near by Lyon in France, the company is currently looking at new solutions for the automotive market, as well as revisiting some ideas that have, in the past, had mixed fortunes. On a heavy-duty engine, most of the friction comes from the cylinder, piston assembly and bearings; but in a passenger car, the valvetrain contributes to a much larger part of the friction. In cars, we make use of friction modifiers, which reduce friction in the valvetrain; but in heavy-duty applications these modifiers have little or no effect – the only way to improve friction levels is to lower viscosity.”

While Euro 6 – and the regulations before that – have served to make engines far more efficient, attention now needs to turn to the next wave of legislation: the drive to reduce CO₂ levels is leading to ever-thinner oils. Many OEMs are looking to 2021 when tighter CO₂ emission limits of 95g/km in Europe are set to come into force. TOTAL, a forerunner in this domain, has been focusing since many years on Fuel Economy lubricants, namely lower viscosity lubricants, which have to be developed with no impact on cleanliness or wear. Ultimately, the number one priority is protecting the engine and the challenge is giving OEMs the best lubricants to do this.

Low viscosity oils in the region of 0W20 and 5W20 will become more common in the future. In addition, courtesy of some Japanese OEMs, 0W16 and 0W4 0W8 grade automotive oils are not inconceivable.

However, the pressure to design and develop increasingly thinner oils impacts on the additives used, something that our TOTAL engineers are well aware of: We are being challenged to put materials in the additives that make the oil appear thicker in the contact zone. So, if you take a cam and tappet combination, or a piston ring’s contact in the cylinder or bearings, as the oil gets thinner there is more likelihood that there will be metal-to-metal contact, so we have to put some new polymeric technologies into the oil to maintain the separation of the metal parts.

Friction modifiers represent a huge investment for us, because when we make changes to our additive technology, it means we have to spend millions of dollars on engine tests to prove out the technology.

Our engineers try to find out exactly what happens to the lubricant as it flows around the engine, and specifically, as it travels from the sump, through the oil pump and filter, and then into the components and subsystems that it is formulated to protect. “We use this approach because of the increased technology complexity that we face in today’s engines,” explains an automotive engineer. “We need a much more engineering-focused approach, where we look at the modeling in detail and the loading within a specific engine component and the bearings in the engine system. This modeling helps us understand in detail the environment that the lubricant has to deal with in terms of pressures, temperatures and loads. By building up a viscometric profile of a lubricant, you have to look at how you define that information and use the knowledge to create a lubricant for the entire engine system.

Such an approach is going to be even more engineering-orientated in the future. “OEMs are using analysis tools to design engines with very little iteration in the development stages, and that is what we are trying to get to with lubricant design,” he explains.

“We plan to use the same tools as the OEMs do – and some that they don’t – to go into finer detail and smaller level, molecular level modeling. This will allow us to really probe the operating environment and see what properties we are trying to refine into the vehicle, and design these properties for pressures and temperatures that they encounter in the components and subsystems, rather than just based on a sump temperature, which doesn’t tell you a lot.”These systems will make a big difference to the next generation of vehicles, both in terms of emissions as well as performance. “As we look to the future, we are seeing downsizing, boosting and hybridization of the engine taken to new levels, which is changing its architecture and operation to the likes of which we have never seen before”. The key to getting the best results is working with the chemists who are at the very core of lubricant research and development: “We are looking for new ways to describe the lubricant that ultimately might not be easy for chemists or formulators to understand, because the formulation will be dictated by a simulation, and the validation of that simulation.

“In the future, we will analyze the engine and the lubricants part in fine detail, and then describe things much better; that helps the formulator define more richly the properties of the lubricant. This approach will allow our scientists to use technologies similar to CAD CAM, which our engineers have been using for the past 30 years.” It offers a lot of potential to improve lubricants and therefore engine performance and life: “We will be able to zoom into the engine and describe things at a much more molecular level, which is great for interaction with the chemists.”

We are increasingly involved with engine programs at a very early stage of the product life, which gives the OEM the best opportunity to cut friction levels in the engine. The task is trying to reduce the drag between engine components, because lubricants are designed to keep things moving, so just by being there, they cause drag. Broadly it can be done by reducing viscosity at the start of the cycle when the lubricant is cold and we can make big changes to the cold temperature viscosity temperature. We can offer big benefits to OEMs where we can optimize the viscometrics of the lubricant for a vehicle.

Driving down emissions, improving fuel economy, enhancing performance and bettering durability are four key goals that all lubricant developers share - these targets will continue to loom large for OEMs as well. However, some technologies will change in response to developments in engine applications and greater R&D efforts from the vehicle manufacturers: “What OEMs have done to combat NO_x and PM is to use exhaust after treatment devices such as DPFs and GPFs. As a consequence we’ve had to develop low sulfated ash and phosphorus sulfur oils, because the ash can cause the DPFs and GPFs to become blocked. We’ve gone through a period where NO_x and PM limits have been continuously tightened and they won’t be tightened much further. But this scenario impacts on what we started developing seven or eight years ago in response to this – namely additives that provide the protection for after treatment devices such as DPFs. We’ve had to fundamentally re-think how we formulate our additives to bring that lubricant protection.”

New materials, such as the viscosity modifiers, as well as dispersant technologies, will help the cause: “With the elemental constraints due to the after treatment device systems, and emissions legislation, we can’t put in any metallic-type elements, so we are more looking at the bigger molecules that are in our formulations. Our focus is on organic materials.”

And the final area for improvement is in the starting point for any lubricant – the base oil: as the engines are smaller and hotter, the oil is getting hotter and therefore more prone to oxidation and oxidative thickening. So we have to use an increased level of anti-oxidants to combat that. As such, this process also drives the use of higher quality base oils, to synthetic oils, in order to provide the thermal stability that is needed.