Mercedes-Benz is predicting that its new family of four-cylinder petrol engines, being co-developed with Renault, will equal the fuel efficiency of BMW’s new three-cylinder unit.

In fact the 1.2-litre petrol four and 1.5-litre diesel four will be so good that Mercedes has ruled out a three-cylinder version of the petrol to take on the BMW 1.5-litre triple.

“We won’t have a three-cylinder engine. Our four-cylinder will be as good as BMW’s three-cylinder,” Merc’s head of powertrain strategy Jurgen Doring told Autocar.

Merc’s new four-cylinder engines are a key part of its strategy to moves towards the EU tailpipe emissions target of 95g/km by 2020, a 45g/km reduction on the current 140g/km figure. They will be introduced into the new MFA range of Mercedes models – including the new A-class and B-class – from 2014, as well as the core of Renault’s range.

Despite this march to ever-lower carbon output, Doring says Mercedes will continue to offer large luxury cars in the range, its heartland of sales. “Even in 2020, the Mercedes customer will still be able to buy a big, powerful car,” he predicted.

The secret will be plug-in hybrids, which Doring believes could eventually push tailpipe emissions of some large Mercedes models down to as low as 60g/km. “The E300 hybrid’s 109g/km is just the start,” he said. Doring predicts around one in four future Mercedes will have a plug-in hybrid drivetrain.

Mercedes is also pursuing weight reduction, by setting tougher design targets for the modules that make up the core components in its cars. “Every time we design a new module, the weight target is a reduction of 14 per cent,” said Doring.

Mercedes must also get its engines through the next stage of EU exhaust emissions regs, EU7 due in 2020, which is likely to align NOx limits on petrol and diesel engines.

EU6 due in 2015 allows diesels to produce slightly more NOx.

Doring says that Merc’s Bluetec diesel technology, which neutralises NOx with the ad-Blue exhaust gas treatment, can easily be re-tuned to deal with EU7 standards.

‘Blue Tec is already prepared for that. We can simply adjust with the amount of ad-blue fluid we use. Manufacturers using de-NOx catalysts will need to put in more material and that will be expensive,’ he said.