2008 BMW Hydrogen 7 Review

Specifications

With the exception of its second fuel filler flap and the ostensible metallic stickers that decree its ability to run on clean energy, the BMW Hydrogen 7 looks nearly identical to a long wheelbase 7-Series. Behind the wheel, it also drives like a 7-Series. That pretty much sums up the purpose of the Hydrogen 7 - to make a car currently available for purchase operate on a super-clean fuel of tomorrow.

Where most hydrogen-fueled vehicles use a fuel cell, the process in which hydrogen is burned to produce electricity, the Hydrogen 7 burns liquid hydrogen in an internal combustion engine. Besides BMW, in recent years only Ford entertained the idea; it developed a fleet of several hydrogen-burning Foci, but has since put priority on developing its HySeries fuel cell vehicle. Though it stands alone in the hydrogen crowd, this route has a number of advantages, from a cost and developmental standpoint.

By converting an existing gasoline engine, in this case the six-litre V12 from the 760Li, BMW was able to focus its efforts of the engine itself, as opposed to reengineering the structure of the car to accommodate electric motors, the fuel cell stack and other specific components. Unlike previous hydrogen-powered BMWs, the E66-generation Hydrogen 7 was designed as if it were a production car, meaning it went through the same processes as would a conventional 750i or 760Li. It meets all the safety tests that enable it to be road legal and though BMW only opted to build 100 of them (many of which can be spotted with celebrities and high-power business people and politicians behind the wheel), each and every one was built at the Dingolfing assembly plant on the same line as the standard 7-Series.

The Hydrogen 7’s bivalent (dual fuel) engine might seem like a complicated entity given its ability to burn both hydrogen and gasoline, but the modifications are far less drastic than what one might imagine. The V12 retains its direct injection fuel injectors for when it runs on gasoline, where the fuel is finely injected directly into the combustion chamber, with air entering via a pair of intake valves. In the case of hydrogen, the fuel is premixed with air then delivered to the combustion chamber via a separate aluminum induction pipe, a method called port injection. Once in the cylinder, the spark plugs initiate combustion to generating power, and the exhaust gases - either a mixture of CO₂, NO_x and other harmful waste gasses, or when running on hydrogen water vapor - leave via the standard valves and through the stainless steel exhaust system.

Facilitating the Hydrogen 7’s internal combustion method required a few other changes to the design of the car, most of which center around accommodating its rather large 43.5-gallon hydrogen storage tank. Despite being a long wheelbase model, the Hydrogen 7’s back seat has been shifted forward considerably, reducing legroom by about four inches. Likewise, trunk space shrinks dramatically, though there’s still enough space to fit a set or two of golf clubs or a couple of small suitcases.

Peel back the trunk’s trim, and you’ll catch a glimpse of the stainless steel tank which holds 17.6 lbs worth of hydrogen at temperatures cold enough to keep John Wayne cryogenically frozen (-418 degree Fahrenheit). Developed by Magna Steyr, the tank shares a lot in common with a thermos; it features an outer layer (stainless), 1.2 inches of vacuum sealed space and 75 layers of aluminum and fiberglass foil, which altogether has the insulation properties of 55.8 feet of styrofoam - more than three times the length of the car. To put this in perspective, if the tank was filled to the brim with ice, it would take 13 years to completely melt. But, because hydrogen evaporates at a much lower temperature than gasoline, it makes the transition into a gaseous state from a liquid by itself, building pressure in the tank. To prevent an explosion, the tank will automatically vent excess gas from a valve in the roof and one underneath the rear of the car. The unfortunate bit is that a full tank of hydrogen has the potential to vanish by itself over the course of ten or so days - another good reason for having a backup of gasoline.

And for those that have thoughts of a four-wheeled Hindenburg, they need not worry. BMW crash tested the Hydrogen 7 in every conceivable way including speeding 18-wheelers, puncture tests against ballistics and even torched the release vent with a blowtorch, and none of these produced leakage or explosion. In the event of a leak, hydrogen dissipates into air faster than gasoline and doesn’t collect in a pool on the ground.

Starting it up, you can hear the faintest difference in sound when it’s running on hydrogen. The port injection system isn’t as well insulated as the standard direct injection system, so it sounds a little louder, but behind the wheel it is impossible to tell what fuel you’re running on. Neither will you feel much of a difference in the way the Hydrogen 7 drives, because it’s otherwise identical to a regular 7-Series. The ZF 6-speed auto shifts seamlessly and the suspension is just as well balanced as ever, keeping the 7-Series’ reputation of agility in tact. This is in spite of it weighing about a quarter ton more.

One of the compromises of having two fueling systems is limitations in power. When running on hydrogen, the six-litre engine produces 256 horsepower and 287 lb-ft of torque. That doesn’t spike to 438 and 444 lb-ft when it’s running on gasoline, the standard output of the 760Li as the outputs are electronically limited. Still, 9.5 seconds to 100 km/h and a 230 km/h top speed is more than enough for day-to-day driving, and the lack of power isn’t distinguishable in an urban setting. In addition, the fuels can be switched over at any point in time, even during acceleration. There’s a momentary hesitation, similar in feel to a gearshift, but no clunking or abruptness. Best of all, the Hydrogen 7 feels natural. It doesn’t have the eerie electric motor whir and surge-like acceleration of electric vehicles running on hydrogen, nor does it possess a spongy brake pedal found in cars with regenerative braking. Best of all, with hydraulic power steering and proper performance tires, it grips and steers just like a 7-Series should.

Even though the Hydrogen 7 represents the latest in hydrogen ICE (Internal Combustion Engine) technology, it is effectively running on technology that’s eight years old. Speaking with Alvaro Sousa, hydrogen project manager, he admits that the car’s efficiency could be further improved by running it solely on hydrogen and using newer technologies. The Hydrogen 7 uses 8.4 lbs of hydrogen per 62 mile increments, which is about 18 to 19 mpg in an average of city and highway driving, limiting its hydrogen-only range to about 125 miles with an extra 310 miles available from the gasoline tank. By comparison, the equally heavy Ford Edge HySeries with its fuel cell system uses 41 mpg in an average of city and highway driving.

But he assured me that there is much more on the horizon for hydrogen. Hydrogen, he says, reacts extremely well to turbocharging and direct injection, not to mention that hydrogen-powered internal combustion engines can be run substantially leaner than their gasoline counterparts. BMW is also investigating downsizing future hydrogen engines and increasing their specific outputs (hp/L). In the future, expect to see six-cylinder and perhaps even four-cylinder turbocharged, direct-injected mono and bivalent BMW hydrogen vehicles.

If there is a stumbling block that could ground the Hydrogen 7 project, it’s a matter of fuel, and not just from a distribution standpoint. The fastest and most cost-effective method of producing this “green” fuel isn’t very green at all. Most industrial-grade hydrogen is generated via a process called reformation that is dependent on fossil fuels, releasing emissions in the process. On its own, the Hydrogen 7 emits five grams of carbon dioxide per kilometer - virtually nothing - but with the reformation process factored in, it rivals an eighteen wheeler in terms of environmental friendliness. Nevertheless, with hydrogen as an automotive fuel still in its infancy, this sort of thing is to be expected. As investment and demand for the fuel are increased, there is the potential to produce hydrogen in a renewable manner (the electrolysis of water into hydrogen and oxygen, for instance - a method which BMW likes).

Perhaps it is a bit childish to think of the car enthusiasts’ needs with topics like global warming and a finite amount of fossil fuels to power performance vehicles, but I like to think of the Hydrogen 7 as a harbinger for car enthusiasts. It is proof that it’s still possible to keep the driving dynamics, the refinement and the mechanical feel of today’s cars, without disregarding environmental responsibility. The world might not be ready to switch to hydrogen, but BMW has proved that the internal combustion engine will live on even if it did. And that’s a good sign for all of us motorheads.