BMW Hydrogen 7 review (prototype)

It’s easy to be sceptical about the concept of a hydrogen powered combustion engine. Spark plugs and pistons aren’t exactly science fiction, are they? Hydrogen is usually associated with fuel cells, which sounds far more futuristically exciting, even compared to a 6.0-litre V12 – and that’s before anyone starts talking about electrodes and chemical reactions. Somehow, using hydrogen for combustion almost seems like…cheating. Even if it’s virtually emission free, and potentially limitless.

However, that V12 provides BMW with a solution to one of hydrogen’s biggest handicap: infrastructure. If there’s nowhere to fill up the tank, what’s the point in building the car in the first place – and if there are no cars that use it, what’s the point of having the infrastructure to supply them? Chickens and eggs, in other words. What’s clever about BMW’s current internal combustion ploy is that the engine is still able to slurp petrol whenever hydrogen isn’t available. It gives the infrastructure the beginnings of a reason to exist without disabling its use in everyday motoring.

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The practical upshot of this is the Hydrogen 7. Looks like a 7 series because it is a 7 series. Based on the long wheelbase 760iL, it’s the spiritual successor to the H2R, BMW’s record breaking hydrogen concept car. Since you can’t physically see the gargantuan development budget, spotting one on the road is best done by the ‘Hydrogen’ badges; from the outside the only differences are the ‘power dome’ bonnet covering the engine modifications, an additional fuel filler cap, and a pair of slender silver-trimmed vents in the rear bumper. If you’re close enough you might also notice the swollen parcel shelf taking a chunk out of rearwards visibility.

But hey, who needs to see behind them when they’re travelling into the future? This bulge, accompanied by a 4.5-inch loss of rear legroom and boot space reduction to 225-litres occurs because BMW had to find somewhere to stash the 170-litre liquid hydrogen fuel tank. This boosts the car’s range to 435 miles – even if only 125 of them are on hydrogen, that’s still more than the exclusively petrol version. Over the rear axle was apparently the safest place the engineers could think of, although once you’re seen the size of the thing you can’t help concluding it was also the only place it would fit.

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The ultimate thermos flask

The tank’s so big because hydrogen takes up lots of space despite weighing very little. It’s 250kg heavy because making hydrogen liquid means cryogenically cooling it to –253 degrees Celsius, and it takes some pretty special design to keep it that way. 75 alternate layers of aluminium foil and fibreglass, vacuum-sealed between stainless steel – equivalent insulation to 17metres of Styrofoam, apparently. Enough to keep boiling coffee undrinkably hot for 80 days. The position of this extra weight forces suspension changes, and a reduction in top speed to 143mph – electronically governed, of course.

Despite using trick carbon fibre reinforced plastic for body panels and additional strengthening, the Hydrogen 7 still weighs 2,460kg. That’s roughly twice as much as a Renault Clio, and more than BMW’s new X5. It’s no rocket ship, either, as the V12 makes only 256bhp whether it’s running on petrol or hydrogen – compared to 439bhp for the standard version. Acceleration is on par with a warm hatchback: 0-62mph in 9.5 seconds. Such petty criticism is rather missing the point, however, when the worst thing coming out of the exhaust is usually water vapour.

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You can’t yet walk into a dealership and say I’d like that one, with the alloy wheel upgrade and a hydrogen tank. But nor is this a one-off prototype, destined for motorshows and then mothballs. The Hydrogen 7 is going through the same development programme as every BMW production car. 100 are being built alongside regular models at the Dingolfing Plant, ready to go on six-month lease in March. Roughly six are heading for the UK, with the others spread out between Europe, the USA, and parts of Asia. BMW isn’t saying who’ll be using them, but expect high-powered movers and shakers, plus the odd cultural icon or two.

Driving on hydrogen: more gargle, less hum

Having spent about three hours driving one, the only significant difference between petrol and hydrogen modes is the engine note. You get more of a gargle than a hum when running on hydrogen. Because the engine management is doing clever things with emissions – nitric oxides, which spike between full and partial throttle load – there’s an occasional kerfuffle when backing off at speed. But you only really feel this through the accelerator pedal, and it’s no worse than a mildly clumsy automatic swapping cogs. Switching between fuels is similarly notable but not dramatic, and performance is otherwise identical. The technology simply works.

Since hydrogen conjures up images of exploding airships and such like, safety is understandably paramount. The car is chock full of active and redundant safety features. There are three batteries, for example, making sure the electronic sensors and controls are never off-line, and even a vent in the roof should the fuel tank pressure go critical – though anyone looking forward to seeing flames shooting out the top of a BMW will be disappointed to learn that hydrogen is not only colourless and odourless, it also burns invisibly, too.

Driving the standard 7-Series

The vents in the rear bumper take care of less extreme pressure release – necessary because heat soak into the tank causes it to built up whenever the car is parked for over 17 hours. This situation means a half-filled tank empties itself in just nine days – one of the limitations of the current design. Refuelling is straightforward, however, as you simply clip what looks like an enlarged vacuum cleaner attachment to the car and let the pump get on with it. There are already three filling stations in Germany, plus a few others around the world, and even some mobile units.

Back to the present

BMW is championing liquid hydrogen over gas because it’s easier to transport and 75% more energy efficient in use. There remains an issue of supply, but once that’s cracked – and hydrogen is the most abundant element on Earth – if you think we’ve done well out of oil you’re in for a pleasant surprise. With vehicles like the Hydrogen 7 providing the impetus, it’s becoming increasingly possible to visualise this potential. With real-world functionality that fuel cells can currently only imagine, internal combustion might seem old fashioned, but BMW seems to be onto something.

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