Road test: Mercedes-Benz B Class F-Cell
April 20, 2011
What's it like to drive a hydrogen powered car? It depends on which one. In the case of BMW's Hydrogen 7, essentially a 760i with its 6.0 liter V12 tweaked to burn hydrogen instead of petrol, one might suspect it's pretty much like the donor vehicle. In the case of Mercedes-Benz's B Class-based F Cell, powered by electricity from a lithium-ion battery pack fed by an on-board fuel cell, you might think different.
Surprisingly, it's not. Mercedes-Benz is currently taking a small fleet of hydrogen fuel cell-powered vehicles (with a rather large entourage of management and refuel vehicles in attendance) on a round-the-world trek through 14 countries. We caught up with the fleet during the recent Australian visit where Benz gave local media a drive through the inner suburbs of Sydney.
What struck most inductees, including your correspondent, was how similar the car is in feel to a conventional IC engine. This is no fluke: Daimler's engineers have put considerable effort into making it thus, to minimize the shock of the new.
At the turn of the key, it comes to life with a whirr straight out of Dr Who's props department. But whatever space-ageness there might be in this is countered by the cockpit. It's surprisingly conventional, meaning there's very little effort required to adapting from a normal car.
If you've ever driven an existing B Class, such is the physical similarity indoors that you might need to take a second look at the instruments to tell the difference. But there are differences. In place of the tacho is a power output gauge, while the center console houses a screen with a bar-graph arrangement showing instantaneous and average hydrogen consumption.
But it's in the driving dynamics that the F Cell delivers the biggest surprise – which is to say, not that much surprise at all. Left to its own devices, an electric motor delivers very little engine braking on its equivalent of a trailing throttle – that is, when your foot comes off the accelerator.
More so in today's early EVs, most of which carry a fair bit more weight than their IC engined donor vehicles. In the case of the 1700kg F Cell, that extra burden amounts to about 300kg. That would normally require plenty of brakework to slow. But no – thanks to some conscious tweaking of the powertrain management unit, it feels just like the cars we're used to.
Not that it doesn't require some relearning to get the best out of the motor and the most out of the F Cell's 4kg of hydrogen. Benz says this is enough for up to 400km (249 miles) of driving range. But to get anything like that out of it, we quickly learned, takes a bit of care and a light right foot. Not just on the go-pedal, but on the brake as well. The reason: when you hit the brake you're destroying momentum artificially. That's momentum you've spent valuable fuel building up, only to flush it away at the drop of an anchor.
In the first couple of kays, the F Cell's trip computer calculated I was using 1.44kg/100km. That, I learned, isn't good. It's a sort of zero-emissions answer to the way those fully sik boyz with funny hairdos get around in their Supras and Godzilla-lites on Friday night, without the histrionics. According to the trip computer, driving like that I'd get about 230km on a near-full tank of hydrogen. Emptying a 4kg tank of hydrogen, incidentally, pumps enough water vapour out the exhaust to turn into about 36 liters of water.
This powertrain works at roughly double the energy efficiency of an IC engine. Benz officials estimate the fuel cell itself works at levels of about 60-70 per cent. With progress through the rest of the powertrain, this ends up diluted down to about 30-40 per cent. Most petrol burners are down round 10 per cent; diesels a little more and hybrids a little more again (anything using IC loses much in waste heat).
Under instruction from Arwed Niestroj, senior manager of Daimler's fuel cell fleet operations, we learned that the key is mindfulness. It's all about looking ahead in anticipation of where you're going to have to slow. First up, that means not building up speed you're going to waste.
Like an IC engine, the F Cell has a fuel efficiency sweet spot that's easy to find using the power output gauge. In urban traffic, according to Niestroj, it's normally around the 20kW mark. We found that's fine for speeds of 40-60km/h, to keep you going with the flow around you. When you know you're going into a corner ahead, it's best to lift your foot early, letting the motor wash off the speed rather than powering up to the corner and hitting the brakes. You don't have to brake to activate the car's energy regeneration system. That happens even during passive deceleration – lift your foot and the power output gauge plunges below zero to confirm it.
It wasn't long before my fuel consumption average dropped to around 0.8kg/100km. And that was with the air on. Turning that off yields palpable improvement almost immediately, Niestroj said.
Once you're used to it, it's not hard to get around on less 1.0kg/100km. In well-to-wheels terms, that works out at the energy consumption equivalent of about 3.3L/100km of diesel. But while the diesel driver is stuck there, a fuel cell car can get much closer to genuine zero emissions if the hydrogen is extracted by renewable means. This is already being done, with much research going into finding commercially viable interpretations.
Not, incidentally, that the F Cell can't come good with a snappy answer when you ask it the question. Putting your foot to the floor produces a surprising surge of acceleration – worthy of a decent petrol four – although the lack of commensurate drama from under the bonnet takes a little getting used to. It's not bad round corners, either, thanks to a low centre of gravity with the fuel cell stack and battery pack
The F-Cell's handling benefits from its low center of gravity, with all that extra weight nestling between the two layers of the B Class's signature sandwich floor.
Which brings us to the question of how similar this vehicle is to the one Benz will be rolling into showrooms in 2015. The answer is: not that similar at all. For a start, the company is dispensing with that sandwich floor in the next generation A/B Class, due out later this year. This we can sheet home partly to leaps forward in secondary safety since the A Class debuted in 1997.
But mainly, it's to take advantage of the vast array of new components coming onto the wholesale market from manufacturers like Bosch, Siemens, big Koreans like Samsung or LG and, of course, the Chinese. Most are forging ahead with technologies made to go under bonnets – to keep the sandwich floor is to risk being overtaken by competitors taking advantage of the economies of scale on offer.
So the sample Benz is serving up on the World Drive probably bears little in common with the final product of 2015. But it's only going to get lighter and more efficient.
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