Q&A: Can Mercedes’ new engine save diesel?

Diesel. Bit of a sore point at the moment, what with the repercussions of that-which-shall-not-be-named still reverberating. It’s probably unwise then, to announce you’ve just spent enough money to launch your own space programme on a diesel engine that’ll power pretty much every car you build.

Mercedes disagrees. Which is just as well, as we’ve had a poke around its engine test plant in Stuttgart, to see where some of the €2.6 billion spent on its new diesel engine has been splashed.

Yes, we are fully aware that a new diesel engine doesn’t sound all that exciting, but you are going to be hearing an awful lot about it for at least the next decade. The humble, snappily titled ‘OM564’ engine is the new backbone of Mercedes. From A-class to S-class, from GLA to GLS, it’ll be everywhere.

Better be good, then?

We’ll find out just how good when we drive the new Mercedes E-class in a few weeks. That’s the first car to get the new four-cylinder turbodiesel, in 193bhp ‘E220d’ form. There’ll be an E200d with around 150bhp soon after too. And then lots more engines after that.

How so?

Like BMW, Mercedes has settled on a modular idea. Think of the engine as a family of 500cc cylinders, which can be linked together however Mercedes fancies. Four cylinders = a 2.0-litre engine, ideal for the C-class, E-class, and hybrid or entry-level CLS, S-class and SUV models. Lop a pot off and you get a 1.5-litre 3-cyl, handy for smaller cars like the A-class and CLA, you might imagine.

Or, steering six in a line for a 3.0-litre straight-six. Want more power? Bolt on another turbo – and in the future, add some hybrid e-boost…

Makes sense. Got any titbits on this new engine then?

It’s a clever bit of kit, on paper. Thanks to an aluminium block (usually diesels are steel, to cope with the immense pressure of ignition), the entire engine only weighs 168kg. It’s got steel pistons instead to cope with the force inside the engine, but they’re a unique shape to reduce soot build-up, and run in a motorsport-spec ‘nanoslide’ cylinder coating. 

Some headline stats, if you please?

The OM654 (yup, now we see why Jaguar called its new diesel ‘Ingenium’ instead) has 24 per cent less friction than the rattly 2.1-litre engine it replaces. It’s also 17kg lighter, and emits 13% less CO2 and a massive 80% less NOx. Meanwhile, power output is up by 24bhp, and the engine itself spins up 11% more quickly. Oh, and it’s 40% thermal efficient, which means Toyota’s record for the new Prius’ engine lasted about twenty minutes. 

How so clean?

Because this is not so much an engine as a sewage treatment plant on wheels. See, usually diesel engines like this run their cylinders at a 15-degree angle, but in the Benz they’re standing straight up to attention, so there’s room down the side of the engine for a massive amount of exhaust cleaning gubbins.

Once the engine has burned the fuel as cleanly as possible, what with its lower internal friction, the exhaust gases go through a sort of assault course of cleaning measures. After spooling up the turbo, the gases are mixed with AdBlue additive (it’s basically made of pig urine). You can buy this stuff from motorway service stations, or your dealer will top up the AdBlue tank at every service. It’s already common in diesel cars, but rather than getting to work as the gases are already on their way down the tailpipe, the new engine crams all the cleaning gear right into the engine architecture itself. 

This means that the AdBlue evaporates faster and more evenly, so your diesel particulate filter (which catches the microscopies particles that aren’t very kind to human lungs) doesn’t get clogged and stop working properly. Then there are two stages of nitrogen oxide filtration, and after the gases have passed that, they enter the regular exhaust system and travel down the tailpipe to the catalytic converter and out of the car itself.

It’s not the sort of sexy, heroic engineering that makes Ferrari V12s and Pagani gear linkages bedroom wall fodder, but you have to doff your cap to the chemistry going on under the surface here to give the torquey, frugal diesel engines we’ve become spoiled by a future.

What about performance cars? No electric turbocharging?

Nope, not here, and don’t hold your breath for it either. Peter Lückert, Mercedes’ Head of Diesel Engines, (Powertrain and Injection department, natch) shrugs off the idea, telling us “We don’t foresee e-turbos being big in the near future. [take that, Audi, and your RS5 TDI concept…] A two-stage regular turbo is better – an e-turbo is too complex, which will stop it being a big trend in the market. We’ll save that for our Formula One car…”

Did Mercedes have to take this stuff back to the drawing board after dieselgate broke?

Apparently not, though you can bet it caused a few sweaty evenings back at HQ. Mercedes was already in the final stages of signing off the OM654 powerplant, running engines on the company’s 72-bay testbed (which is relentlessly online 24/7, 365 days a year, and has lights powered by the dyno’ed engines) when the incredible news started to break in America that VW’s engines weren’t as green as officially stated. At this point, the engines had been on the dynos for a combined 25,000 hours.

“We didn’t have to change the engine itself”, Lückert explains. “Our biggest fear was that diesel could end up being banned, or over-taxed, if the mainstream media continued to mis-report about it.”