Engine development has progressed from the long stroke, low revolution engines of the 1920s to the high revving short stroke Formula One machines of today. This evolution has pressured manufacturers into providing components that can survive in this increasingly harsh operating environment. Part of this progress is down to more durable and lightweight materials, reducing component stress, but an increasingly important contribution is being made by revolutionary surface treatment resulting in reduced friction and improved lubrication characteristics.
Why the need for greater efficiency?
Recently, however, the motor industry has been prompted to develop new and innovative ways of making engines more efficient, quieter and a lot more eco friendly. For as long as we can remember, motor manufacturers have been telling us how much more fuel efficient each successive vehicle model is, over its predecessor. Now, EU regulations dictate how efficient cars need to be and manufacturers have to meet certain emission targets, or face the wrath of the authorities and possible loss in sales.
Biofuels have become the hot topic recently, prompting a flurry of research activity on the part of the manufacturers to explore the use of renewable fuels, thereby approaching a CO2 neutral emissions state. Biofuels are greener and importantly, they are renewable because they use food oils which can be produced locally in most countries. This production opportunity has obvious benefits for the farming communities locally, as well as reducing the importation of foreign oil and promoting local energy production.
The effect of biodiesel on the engine in detail
The purpose in using biofuels is to eliminate engine emissions and this can be achieved in two ways. Firstly, the use of biofuel reduces emissions through its ultra low sulphur content, while the fact that biofuels are derived from a renewable source also contributes to lower emissions.
However, the use of a different fuel, or changing the mixtures of biofuel and regular fuel, will alter the lubricating characteristics of that fuel. But questions have arisen over the tribological behaviour of systems such as the valve train, fuel injection, and the piston assembly when introducing the new oils and fuels.
Biofuels are known to be responsible for increased corrosion and component wear within the engine as a result of the change in the lubricity of the fuel. Attention in the motor industry is now focused on how harsh these new fuels can be on engine components, but especially in the injection system and the fuel pump, as these components are in immediate and direct contact with the biofuel.
As the proportion of the renewable element in the biofuel is increased, so the effects of corrosion and component wear will also increase. At present, the bio-element is still quite small, and as Mark Boghe, Product Market Manager Automotive & Racing at Bekaert, says, “Everybody is looking to see where this whole bio-thing goes, whether it will stop at E85 [only 15% mixture] and how soon that will come. So they continue researching for now, albeit hesitantly,
because if the mixture proportion remains relatively low, then you don’t need to pour a lot more investment into it”.
The trickle down of racing solutions to automotive applications
As we have seen, the use of biofuel changes the tribological behaviour of several components in the engine, leading to increased wear of different components. There is, however, an almost off-the-shelf solution which can be adapted from the high tech world of motorsport that can reduce the corrosive and wear characteristics of biofuels.
As modern engines move into the high revving, high compression regions producing greater performance, they need to borrow the technology so successfully used in racing engines. By coating those surfaces that wear most rapidly, from fuel injection to valve train components, the engine builder can provide a more reliable power plant to their buyers.
One can justifiably ask, therefore, what relevance does motorsport have to an energy efficient automotive platform, and the automatic response is usually ‘none’. Contrary to popular belief, however, motorsport has at its heart an inherent driving force to be efficient, economical and cost effective.
As Chris Aylett, CEO of the Motorsport Industry Association points out, “At the heart of motorsport, since its early days, is the efficient use of a given amount of energy which, in most cases, is a fuel tank of gasoline. This focus on gaining maximum efficiency from that energy allocation is the absolute opposite of the general perception. As the weight penalty associated with carrying fuel/energy is so high, race engineers have become expert at delivering maximum power and efficiency from the engine using minimum fuel/weight.”
In racing terms, increased performance translates into greater power and speed with improved efficiency. The purpose of using coatings in Formula 1 is not so much to reduce fuel consumption but to produce additional power, although they are also considering fuel consumption and they might be pushed more in this direction in the near future. Those same techniques that keep an Audi running at record speeds for 24 hours are now finding applications in the consumer and business markets.
The emissions outlets suffer because the natural by-product of combustion are carbon deposits. As small, super hard particulates flow through the filters, they come in contact with the moving parts and gouge them in a significant manner. If those parts are harder than the particulates, simple physics dictate that they are crushed and absorbed; DLC coatings are usually stronger than whatever goes into the engine. Bekaert have found that under scrutiny, the trickle-down effect of this high efficiency technology in motorsport can benefit the manufacturer of everyday production cars.
DLC coatings – the industry’s response
DLC coatings are a combination of the graphite and diamond structures of carbon. This blend leads to a range of coatings that combine exceptional hardness and wear-resistance, with low friction. DLC coatings are also inherently self-lubricating.
For Bekaert, the development of DLC coatings started in their racing applications, where engineers were looking for solutions to high wear problems as a result of increasing contact pressure on engine components. Because they could not harden the components any further, they began looking for other solutions to make the component’s contact surfaces harder, and DLC coatings provided a significant solution to this problem. DLC coatings have the advantage of adding not only a high hardness element but at the same time also low friction characteristics.
Boghe elaborates: “The benefit is great because you don’t only give the component high hardness, thereby protecting the part, but by reducing the friction, you also reduce the wear impact on the parts and their counterparts as well”.
In addition, DLC coatings are very inert which means that they do not react with the counterpart as the coating forms an amorphous carbon layer on the surface of the component. The DLC coating also has no affinity with the counterpart thereby eliminating the tendency of seizing or welding when one rubs the surfaces of two similar materials together under pressure.
For Bekaert, an important breakthrough in the application of this technology, and therefore also its effectiveness, has been in how the DLC coating is made to stick to the component surface. Mark Boghe explains: “For racing applications, we developed a coating architecture, or let us say, a stack of different layers to make a DLC coating adhere very well to the substrate”.
For high volume applications, Bekaert uses a similar structure which is basically an adhesion layer which acts as a shock absorber. This is followed by a gradient layer to which the very hard DLC coating is then applied. This technology has been borrowed from their experience in racing, where they quickly learned that it is not good enough to just apply a hard DLC layer straight onto the component surface, but that there needs to be a very careful build up of the layers.
Looking at the applications today, it is fair to say that all diesel cars that have common rail or high pressure injection use this type of technology on their diesel injection components. This technology was first used some ten years ago on the Volkswagen Tdi engine, and this DLC coating technology has been constantly fine tuned during the last decade through both motorsport and production vehicle applications.
At that time the carbon layers were not the same as they are today, but as internal engine pressures have increased, manufacturers have been forced to apply DLC coatings to more components, while the coatings themselves have become more wear resistant.
An application where this technology is focussed at present is in the area of friction reduction, mainly in the valve train assembly and components. By considering the energy that is wasted through friction, the friction reducing DLC coatings will contribute to a more efficient engine, thereby decreasing emissions. Preventing wear-related damage to biodiesel driven engine parts is currently a high profile issue in the automotive industry, along with efforts to reduce fuel consumption.
The latest test results conducted by Bekaert conclusively demonstrate how Bekaert Dylyn® Plus coatings effectively address customer needs for higher
engine output and improved fuel consumption. Uncoated fingers are the current standard reference in the market and typically show signs of wear within 8 hours, however, fingers coated with Bekaert Dylyn® Plus, easily surpassed a 300-hour wear test. Bekaert’s researchers also determined that the uncoated counterpart of the coated engine element did not start to wear as a result of the hard Bekaert Dylyn® Plus coating.
This friction reduction translates into reduced consumption of fuel, establishing Bekaert Dylyn® Plus coated components as a differentiator in the market of biodiesel-driven engines. Although DLC performance tests were conducted using coated components in a motorcycle engine running at very high revs (a typical non-biodiesel-driven engine), these results nevertheless do offer positive news for the technical challenges in increasing performance in a biodiesel-driven engine.
From racing to automotive and beyond
Products and components developed in the harsh race engine environment have helped engineers to increase engine revolutions, compression ratios, power and speed. This has been largely possible due to the longevity and hard-wearing nature of new materials and surface treatment and coatings, as well as more robust lubrication at higher temperatures.
As stated earlier, one of the best classrooms in which to test new products and applications is the race track, and Bekaert have observed an increase in demand for DLC coatings on valves in the NASCAR market, where these coatings provide a solution to the problems caused on the intake valves by unleaded fuel. There is also growing interest in DLC coatings of aluminum pistons for friction reduction, also resulting in increased performance.
Bekaert’s extensive testing of valve train components has shown that by coating the tappets, you can reduce fuel consumption and therefore CO2 emissions by between 1-2%. Although this may not sound like a substantial improvement, when multiplied by the 49.3-million passenger cars produced in 2006 alone, it would contribute significantly to a reduction in CO2 emissions globally. The US alone consumes in excess of 20.0-million barrels of oil per day, and with our finite oil reserves dwindling fast, more efficient use of this precious commodity would be prudent and advanced surface technology would be a step in the right direction.
One of the biggest advantages in the application of DLC coatings to valve train components is that this technology can be introduced without changing anything in their logistics or vehicle assembly process. Manufacturers can basically use the same engine design and install a coated component instead of an uncoated component.
With more than 10 years’ experience in this field, Bekaert is now the number one supplier to the Formula 1, Rally, DTM, Formula 3 and NASCAR industries with their high quality DLC, marketed worldwide under the trade name Cavidur®. Cavidur® provides the most reliable surface engineered solutions for highly loaded engine components.
Bekaert, now a worldwide leader in racing and automotive component coating solutions, recently announced an expansion to its production facilities in Europe and the US. This will enable Bekaert to accommodate the increase in demand for its coatings for automotive and race car engines.
The new state of the art, proprietary coating equipment has enabled Bekaert to enter high-volume automotive markets, while delivering reliable and high performance diamond-like coatings. There is little doubt that competition seeks to improve performance and the old adage of ‘win on Sunday, sell on Monday’ holds true here, because lessons learnt on the race track have enabled Bekaert to transfer this experience to normal passenger car production around the globe.
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