Mercedes hybrid chief pans BMW hydrogen

MERCEDES-BENZ has poured cold water over BMW’s emphasis on vehicles using hydrogen-powered conventional engines as an alternative to fuel cells.

BMW released details last week of the world’s first series production hydrogen-burning vehicle, which is based on the 7 Series luxury sedan and uses a 191kW/390Nm 6.0-litre V12 engine that runs on both liquid hydrogen and premium-unleaded petrol.

Comparing it to fuel cell power, BMW said the hydrogen combustion engine – which the company claims can send the vehicle from 0-100km/h in 9.5 seconds, on its way to an electronically limited 230km/h top speed – developed "much more engine power” and combined “dynamic performance, superior comfort and the enhanced safety in a manner typical of all BMWs".

But the executive director of hybrid powertrain programs for DaimlerChrysler, Dr Andreas Truckenbrodt, has told GoAuto that he did not believe a hydrogen-powered conventional engine was a better alternative to fuel cells as the primary source of propulsion.

"We do not believe so for a couple of reasons," he said. "One reason is the big benefit of the fuel cell is the double – twice as high – efficiency as a combustion engine.

"It requires a little bit more energy to produce the hydrogen, so if you then burn it with the same lousy – well, not lousy, but the same – efficiency as the combustion engine you’re not gaining too much. So that’s why we think if you are using hydrogen, then please use it in the better-efficiency propulsion unit, which is the fuel cell.

"The other thing is, if you burn hydrogen you’re not emissions-free. That’s where we think the big benefit of fuel cell is – being emissions-free." Mercedes-Benz and BMW are alliance partners (with General Motors) on hybrid technology, however the issue over automotive fuel cells has split the two German luxury-car marques.

BMW said last week that it considered fuel cells as a means for providing auxiliary power – that is, electric power for the onboard network of a petrol or hydrogen car – but it remained one of the few major car manufacturers (Mazda is another) touting the hydrogen-fuelled internal combustion engine as a significant powertrain of the future.

BMW said that when running in hydrogen mode the new Hydrogen 7 car "basically emits nothing but vapour" although it did admit that "if at all, minute HC (hydrocarbon), CO (carbon monoxide) and CO2 (carbon dioxide) emissions will be generated by the combustion of lubricant and by rinsing the activated carbon filter while running in the hydrogen mode".

"The only relevant factor … is the emission of nitric oxides (NOX) generated, above all, at particularly high combustion temperatures," BMW said in a statement.

"Highly flexible combustion management, however, allows an operating strategy able to largely control the formation of NOX. In practice, this means that the engine is run under part load with a high share of oxygen and, accordingly, a high lambda factor of more than two. In this case the temperatures in the combustion process are relatively low, keeping NOX emissions to an absolute minimum." Dr Truckenbrodt acknowledged that it was a mistake to think fuel-cell vehicles would overtake all other systems any time soon. However, he remained committed to the technology.

"I personally am very much convinced that fuel cells are a realistic option. The only point which maybe 10 years ago was totally over-estimated was how fast we’ll get there, how fast we’ll get the technology advancement and the costs down – but it will be." BMW’s Hydrogen 7 car will enter production next year, and although pricing is still to be announced the company has said the car will be leased to selected customers rather than sold.

It intends to build only a few hundred examples and its market appeal will be limited considering there are only about 10 hydrogen refuelling stations worldwide, none of which are located in Australia.

The Hydrogen 7 has a cruising range in hydrogen mode of around 200km, with another 500km in petrol mode.