Mercedes-Benz B-Class F-Cell 2011 Review

Mercedes-Benz B-Class F-Cell

In preparing to put a hydrogen fuel cell-powered B-Class to market in 2015, Mercedes-Benz has sent a small fleet of the cars on a four-month circumnavigation of the globe. By its completion mid-year, the trip will have taken in 14 countries, four continents and all manner of climatic and road conditions. Its aim is to prove the technology is fast approaching the maturity it needs for arrival in mainstream showrooms.

The car that goes to market then will be some way removed from the prototypes we have here today. For a start, it won't have the hallmark A/B-Class sandwich floor. Benz is dispensing with that in a major makeover to the platform due late this year.

And by virtue of rapid improvements in each element of the technology, the company also expects the market-ready F-Cell to be considerably lighter than this one which, at just over 1700kg, carries a 300kg premium over its conventionally powered donor vehicle.

Nevertheless, a drive around the back streets Pyrmont and Sydney's Darling Harbour precinct provided a useful pointer to what to expect.

It starts with the turn of a key, just like a normal car. In place of the normal engine noise there's a whirr. But in its accelerative and decelerative behaviour the powertrain feels surprisingly similar to an IC one. That's no coincidence. To help garner mainstream acceptance, Benz has put considerable work into making sure of it. For example, they've calibrated the electric motor's management system to emulate engine braking when you bring your foot up.

"Engine braking isn't natural to electric motors, but it would just feel too weird to drivers without it," explained Arwed Niestroj, senior manager of Daimler's fuel cell fleet operations, accompanying Carsales Network on our ride.

Niestroj says the feel of this car is the result of a conscious effort to feel 'normal'. "But it retains the operating efficiency of an electric car. The overall energy efficiency of a normal IC powertrain comes to about 10-15 per cent, depending on how you set it up. With a hybrid it can get a bit better, but the thermodynamic processes of [converting thermal into kinetic energy using internal combustion] just aren't very efficient.

In the early part of my run, the system calculated I was using 1.44kg/100km. That, says Niestroj, is "pretty bad – about what you get when you go, maybe, 140km/h all the time." The trip computer agreed: that figure panned out by its calculations to a range of about 230km on a near-full tank of hydrogen.

The key is to drive off the output gauge rather than the speedo. Like an IC engine, the system has a fuel-efficiency sweet spot, somewhere around the 20kW output mark. Keeping it around there felt about right to keep pace with inner Sydney traffic. Take your foot off and the needle drops below zero into the ultra-green dotted area, indicating the car has gone into regenerative mode, replenishing the battery.

With a little care, in no time I had the fuel consumption well below the 1kg/100km mark – down around 0.8, and that was with the air running.

"Without the air conditioning, you're going to notice it's better," Niestroj said.

At the other end of the scale, foot to the floor, it feels surprisingly muscular. This will undoubtedly increase as they work on paring off the 300kg premium the F-Cell carries over its IC counterpart.

Niestroj says the real no-no – the primary indicator of inefficient driving – is braking. Hit the anchors and you're washing off pace you ideally wouldn't have extracted from the system in the first place. Ideally, the driver will only brake to hold the car still at a complete stop. "When I drive this car, I don't brake at all. I let the car do the decelerating."

It's not hard to get your efficiency levels up. The key is heightened anticipation – to watch ahead and take your foot off the throttle well in advance of corners and other reasons to slow. It only took a few minutes to nail it, using the engine braking alone to slow.

Driven efficiently, the F-Cell uses less 1kg of hydrogen per 100km. That equates to about 3.3L/100km of diesel. And that's a well-to-wheels figure, taking into account the carbon emitted during the processes of manufacturing the vehicle and extracting the hydrogen. It will go closer to genuine zero emissions using fuel extracted by solar or other green means.

Unlike other electric vehicles, the F-Cell has an exhaust outlet. In emptying a 4kg tank of hydrogen, it will produce vapour corresponding to around 36 litres of water.

The F-Cell's handling benefits from its low centre of gravity, with all that extra weight mounted in the floor.

Past that, the F-Cell is every bit B Class, with no compromise to interior or cargo space and no exterior evidence of what lies beneath save for the livery.

Asked how conscious the world trip drivers are about their behaviour at the wheel, Niestroj says they're careful without skimping and scrimping.

"On highways we might get up to 30 or 40kW, but we're not always accelerating and braking. It's stable. But we didn't plan for 400km per tank, however. Certainly not for Australia, where we knew we'd use the air conditioning."

What does he consider a realistic hydrogen consumption figure for the unthinking commuter? "On highways in Australian conditions, I think 250 is safe. In urban areas with more stop-start, it's easy to get to 350. But it's not hard to make 400 if you're careful.

"That's the good thing about the car," he adds. "Pay attention and you get very efficient mobility. But you also have the option to drive dynamically, to not pay attention, even though it costs in fuel and therefore range."

"And industrial gas companies like Linde have been separating and storing it for years. It's no big deal for them. The only big deal is setting up the channel – the service station network. (Industrial gas multinational Linde and its local subsidiary, BOC, are providing hydrogen for the World Drive.)

Niestroj says the next generation F-Cell will benefit from Benz's modular approach to powertrain diversity.

The components will be compact enough to fit beneath the bonnet. Helped by advances in safety technology, it's this that has allowed the company to do away with the sandwich floor. "We've learnt enough to come up with a powertrain solution that gives us most of its benefits but which allows us to revert to a conventional powertrain layout."

The primary advantages lie in the cost efficiency of using externally sourced components made for use in what he calls a "classical" front-end layout. But the new platform won't be restricted to that. It's designed to accommodate a huge diversity of powertrains, from all-electric and fuel cell systems through conventionally fuelled IC engines to the natural gas used in its BlueEfficiency systems.
 

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