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Let Us Spray


If life was fair, the prettiest part of Mercedes-Benzs passenger car diesel engines wouldnt be hidden from sight – it would be riding out front like a hood ornament. But deep inside, nano-tribology is making these V6s more resistant to wear, markedly lighter and more fuel efficient. By focusing on eliminating friction losses where the piston moves up and down against the cylinder linings, the engine also can use lower-viscosity oils without sacrificing wear control or long drain intervals.

Its all due to an innovative MB-patented technology called Nanoslide, in which twin-wire arc spraying is used to melt iron/carbon wires and to spray the droplets by gasflow onto the cylinder surfaces of the lightweight aluminum crankcase. This results in a nano-crystalline iron coating which can be finely finished to a nearly mirror-like, smooth surface, says the German automaker.

For the past five years, Nanoslide was used exclusively in the 6.3-liter V8s that go into the pricey Mercedes-AMG. With experience now in around 75,000 AMG engines, the coating technology has been extended to all of MBs series-production V6 diesels.

The ultra-fine finish is created by a special honing process which leaves a thickness of only 0.1 to 0.15 millimeter. Thats a far cry from the heavy grey cast-iron liners – up to 5 millimeters thick – that are applied in most diesel engines. The honing process also exposes pores in the nano-material which are able to retain oil, and thereby ensure optimal lubrication of the piston assembly, Mercedes-Benz explains.

Daimler AG, Mercedes-Benz parent, is leaning on Nanoslide to help it meet Euro 6 emissions targets for 2014. With it, the diesel-powered Mercedes-Benz ML 350 SUV can achieve a combined consumption of 6.8 liters of diesel per 100 kilometers – 24 percent better than its predecessor – and its CO2 emissions have dropped from 235 to 179 grams per kilometer. Neither figure would have been realized without the new Nanoslide technology, the company says.

Nanoslide also cuts the engines weight by 4.3 kilograms, for another 3 percent of fuel savings. In addition to cutting mechanical friction losses by up to 50 percent, versus gray cast-iron cylinder liners, the deposited coating is highly resistant to wear, Mercedes-Benz spokesperson Jens Schaefer in Stuttgart told LubesnGreases.

The overall fuel economy improvement was measured on two kinds of test rigs: Friction comparisons were made between the standard configuration and new Nanoslide technology using tear-down measurements of motored engines, combined with fuel consumption calculations, Schaefer explained. And also New European Driving Cycle tests of fuel consumption in fired engines on dynamic engine test-benches. Both test methods showed consistent results.

The company would not disclose how much it has invested in creating Nanoslide, but said it was developed internally through Daimlers research and advanced engineering, series development and production engineering staffs working very closely together. The iron/carbon wire is not produced by Mercedes-Benz itself, but is an available material that is supplied according to its very strict specifications.

The coating has very good wear resistance, pointed out Schaefer. We detect almost no wear at the cylinder surface during engine lifetime. As for its lubrication needs, theyre simple, she added: Nanoslide technology is an iron-based coating, there is no need to change oil additives or use special oils. Nor is there any plan to change the oil drain intervals for Nanoslide engines.

At the factory, the diesels get Mercedes standard top-tier engine oil meeting the proprietary MB 229.51 specification. This oil is made with API Group IV polyalphaolefin base oils, and can achieve drain intervals of up to 30,000 kilometers (18,000 miles) or two years.

The current factory fill is an SAE 5W-30 viscosity grade, but Nanoslide will allow the use of even lower-viscosity lubricants, which could contribute more fuel efficiency. Due to reduced mixed friction in the cylinder liner/piston ring contact, the reduced hydrodynamic friction of lower-viscosity oils will lead to a real fuel economy benefit, Schaefer remarked. Lighter 0W multigrades already are approved for service fill, but Daimler engineers have been itching to use them for factory fill as well.

Expanding the use of Nanoslide brought another accolade recently: In late October, Mercedes-Benz received Europes prestigious Materialica Design + Technology Award 2011, for outstanding innovation in the Surface & Technology category.

What next? The coatings next horizon may be gasoline fueled engines, not just diesels, revealed Schaefer. The technology is applicable and will be used for both engine types.

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