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Mercedes 'future-proofs' diesel power

Topsy-turvy: Mercedes has reversed the trend of diesel engines with a new four-pot that has steel pistons and an aluminium block.

New diesel family safeguards compression ignition for Mercedes-Benz


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17 Feb 2016

MERCEDES-BENZ has simultaneously returned fire at Jaguar's Ingenium engines while rubbing salt into Volkswagen's wounds, with a new diesel engine family it says sets a new standard in efficiency and emissions.

The all-new OM 654 2.0-litre four-cylinder is the German car-maker's first all-aluminium diesel, and will debut under the bonnet of the next-generation E-Class, reducing its diesel appetite by around 13 per cent.

If it manages the increase in efficiency, when it launches later this year, the new E-Class could use just 4.3 litres of fuel per 100km on the combined cycle, matching the current luxury large economy king – Jaguar's freshly launched XF Prestige 20d.

At the new E220d's debut at the Detroit show in January, Mercedes said the new model's fuel consumption would slip under 4.0L/100km, but final Australian specification is yet to be confirmed.

Despite the reduction in fuel use and a smaller displacement than the outgoing 2.2-litre unit, the new engine has found more grunt per drop, with power rising 18kW to 143kW, and thanks to lightweight construction, has shed 34kg. Torque is unchanged at 400Nm.

In the wake of the unfolding Volkswagen diesel emissions scandal, Mercedes is spruiking the cleanliness of its OM 654 engine claiming the new engine is “future proof” and that the family of modular engines that follow it will “meet all future global emissions standards.”

While VW's 2.0-litre and 3.0-litre diesel engines used a 'defeat device' to cheat the NEDC measurement cycle, Mercedes' new engine has been designed to conform to new more accurately simulated Real Driving Emissions (RDE) testing.

The various benefits to weight, efficiency and emissions are thanks to a significant rethink on how a diesel operates, with innovations in exhaust gas recirculation (EGR) catalytic pollutant conversion and materials technology.

Unlike many compression ignition engines that use a cast iron cylinder block and alloy pistons, the new Mercedes four cylinder reverses that trend, with an aluminium block and highly unusual steel pistons.

The unorthodox pistons stroke what Mercedes calls Nanoslide-coated cylinders, which is a process that sprays molten iron/carbon alloy onto the iron cylinder liner, producing an extremely smooth, low-friction finish.

With more conventional emission-reductions systems, a single catalyst is located at a point downstream from the engine in the exhaust system, but Mercedes has installed two catalysts directly on the OM 654 engine.

With such a close proximity to the hot exhaust gasses, Mercedes says the critical cat light-off temperature is reached immediately after the engine is started, unlike other approaches, which require a warm-up period.

Multiway EGR returns a small quantity of exhaust gasses to the combustion chamber to reduce oxides of nitrogen (NOX) and other pollutants before catalytic treatment.

After the gasses emerge from the turbocharger turbine they first enter an oxidation cat, then go into a downdraught AdBlue mixer which doses the gas with urea, for further NOX reduction in a second Selective Catalytic Reduction system (SCR).

Before entering the exhaust silencers, the gas passes through a final particulate filter to remove solid particles that produce the black smoke and soot which is associated with older diesel engine technology.

Daimler board member with responsibility for group research and head of Mercedes-Benz Cars development Thomas Weber said the new family of engines secured the future of diesel power for Mercedes light and heavy vehicles.

“In our opinion, the diesel engine is indispensable in trucks and cars if we want to further reduce the CO2 emissions from traffic,” he said.

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