“The mono-fuel Hydrogen 7 is the (result) of more than 25 years of hydrogen development by BMW,” noted Tom Baloga, vice president of engineering for BMW in the United States. “It demonstrates BMW’s support for a hydrogen infrastructure by producing an internal combustion engine that produces truly near-zero emissions and simultaneously cleans the air of certain pollutants.”
The previous version of the BMW Hydrogen 7 did have one key advantage: If the lightweight gas wasn’t available, a motorist could switch to gasoline and keep running. But the downside is that the car’s big V-12 powertrain had to be compromised to handle both fuels. And that impacted performance, mileage, and emissions, according to BMW officials.
The tiniest amount of NOx does come out of the tailpipe, the natural result of the compression-ignition cycle in an internal combustion engine. But "The BMW Hydrogen 7's emissions were only a fraction of SULEV level, making it one of the lowest emitting combustion engine vehicles that have been manufactured," contended Thomas Wallner, a mechanical engineer who leads Argonne's hydrogen vehicle testing activities. "Moreover, the car's engine actively cleans the air. Argonne's testing shows that the Hydrogen 7's 12-cylinder engine actually shows emissions levels that, for certain components, such as Non Methane Organic Gases (NMOG’s) and Carbon Monoxides (CO’s), are cleaner than the ambient air that comes into the car's engine."
BMW’s approach to hydrogen is unusual, though not entirely unique. Most manufacturers working with this “green” fuel are using it to run fuel cell stacks. At their most basic, fuel cells combine hydrogen with oxygen from the atmosphere, producing water vapor and electricity. That current can be used to run a vehicle’s electric motors.
Burning hydrogen in an IC engine is generally considered less efficient, but it also makes it easier to switch to the fuel without completely rebuilding the automotive infrastructure. Other makers, including Ford and Mazda, have also been experimenting with this approach, the Japanese maker, for example, field-testing hydrogen-powered versions of the rotary-powered RX-8 sports car.