No water-injection for Mercedes-Benz

Mercedes-Benz is in no rush to follow arch-rival BMW down the water-injection path to lower real-world emissions.

BMW will show its water-injected version of the M4 coupe this summer , and has confirmed that it is working on advancing to direct water-injection systems to cool cylinder temperatures and improve emissions in the real world.

But Mercedes-Benz’s board member in charge of development, Dr Thomas Weber, compared water injection to engines with variable compression ratios, prototypes of which were built and publicised by Peugeot, Saab, Dutch engineering firm Gomecsys and the Finnish researchers, Waulis Motors.

“It’s a little comparable to variable-compression ratios for engines,” Dr Weber said.

“The investment-to-result ratio to put that into production is the key question and that ratio doesn’t work.”

But while Mercedes-Benz continues to keep its eye on water-injection developments, it sees the immediate problems as too difficult to put into production.

“The biggest problem is where the water comes from. So far what we found is that we can cool it (cylinder temperatures) down with combustion but from the efficiency point of view, it’s not the optimal way to do that.”

“We always looked at it at and at each powertrain conference the topic keeps coming up. So far it was only prototypes.”

BMW plans to move water-injection beyond the prototype stage this year, though, and has been running a very public development schedule with its water-injected M4 acting as the MotoGP safety car.

Its board member for development, and the direct counterpart to Dr Weber, is Klaus Fröhlich, who insists the direct-injection version of the water-injection system will deliver more power and far fewer emissions.

“The topic of water-injection directly into the cylinder is very important to me,” Fröhlich said.

“We are going to continue with this in all variants in different drive systems, just as variable valve timing came in all variants.”