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BMW's dual-fuel liquid hydrogen car is way beyond cool

There is nothing unusual about automakers building experimental cars that run on hydrogen. Hundreds are in operation and almost exclusively they are powered by fuel cells that electrochemically combine hydrogen and oxygen to produce electricity and power an electric motor.

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There is nothing unusual about automakers building experimental cars that run on hydrogen. Hundreds are in operation and almost exclusively they are powered by fuel cells that electrochemically combine hydrogen and oxygen to produce electricity and power an electric motor.

But that is not the only way hydrogen can be used as an automotive fuel. While there are some challenges to doing so, it can also be burned directly in an internal combustion engine – with the same near-zero exhaust emissions, apart from water vapour.

That is the route BMW has been pursuing since 1979, and based on the performance of the BMW Hydrogen 7 I drove in Toronto last week, they have the technology just about perfected. So much so that the company is building a series of Hydrogen 7s in limited production for distribution to high-profile, environmentally minded drivers around the world.

They are dual-fuel vehicles capable of running on either hydrogen or gasoline, a necessity because there is as yet a very limited infrastructure for the distribution of hydrogen. It is especially limited for liquid hydrogen, which is the route BMW has chosen to follow.

Most fuel-cell vehicles under development use gaseous hydrogen, which is stored in high-pressure tanks at pressures up to 70 MPa (10,000 psi).

Liquid hydrogen is cryogenic, which means it doesn’t require high pressures for storage, but it does have to be cooled to -253C to remain liquid.

It’s the best way to pack a lot of hydrogen into a small space, for both storage and transportation, explained Jason Perron, one of the BMW engineers working on the project.

The rig for refuelling the Hydrogen 7 looks similar to those used for Indy or Formula 1 cars. About 12 cm in diameter, it fits tightly onto the car’s filler neck, located in its right C-pillar, via a positive coupling, just like on the race cars.

The centre part of the filling tube transfers liquid hydrogen in, while a surrounding chamber vents hydrogen gas out. In a commercial application, that gas, which builds up in the tank as the fuel gradually warms up, would be recovered and cooled down to a liquid state again for subsequent use.

For touring purposes (BMW is touring North America with a fleet of Hydrogen 7s to publicize the technology), the Linde gas company has constructed a mobile refuelling rig to both store and dispense the fuel.

The 160-litre tank in the car is double-walled stainless steel with an aluminum-foil reflective layer and a vacuum between the two walls to minimize heat transfer. BMW says it would take a snowball 13 years to melt inside the tank.

While the hydrogen is stored in liquid form, it is delivered to the engine as a gas, so the tank is never filled more than 80 per cent with liquid. That way, there is always a low-pressure, gaseous component from which fuel is drawn for the engine.

The hydrogen is mixed with incoming air via port-type injectors atop the inlet manifold, which tend to clatter a bit, like a diesel, especially on startup. But that noise cannot be heard from inside the car with the hood closed.

From behind the wheel, the Hydrogen 7’s noise level and performance when running on hydrogen is indistinguishable from that when running on gasoline. A button on the steering wheel lets the driver switch seamlessly between the two fuels, imperceptibly to other passengers in the car.

Because the engine has to be tuned to accommodate both fuels, the performance on either is not quite as strong as with a gasoline-only 7 Series V12; but with a peak output of 260 hp from the big 6.0-litre engine, it is still more than adequate.

According to Alvaro Sousa, another BMW engineer assigned to the Hydrogen 7 project, the next-generation engine currently under development will include direct injection and be optimized to operate exclusively on hydrogen.

But developing such a car creates a chicken-and-egg scenario. It won’t be practical until there is an established hydrogen supply infrastructure to refuel it.

That is one of the reasons for this tour – to demonstrate the clean-air advantages of the technology and encourage those in a position to do so to accelerate the development of a supporting infrastructure.

mgmalloy@aol.com

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