The twelve-cylinder power unit carried over from the BMW 760i as the basis for the engine in BMW Hydrogen 7 offers further benefits highly relevant to the customer. Indeed, the engine comes with all the qualities gained by BMW from decades of experience in the production of particularly powerful and efficient engines, which also means the supreme reliability so typical of a BMW.

Compared with a fuel cell hardly offering the same kind of power, the combustion engine is far lighter right from the start. The use of a combustion engine also means lower cost of production, with the BMW Hydrogen 7 not only having gone through the BMW Group's entire process of series development, but also being fully integrated in the conventional production process as a hydrogen car: The new hydrogen model is built at BMW's Dingolfing Plant parallel to the other models in the BMW 7, 6 and 5 Series, with the drive unit in BMW Hydrogen 7 coming like all BMW twelve-cylinders from the Company's engine production plant in Munich.



Direct gasoline injection and hydrogen intake manifold supply

The hydrogen combustion engine is based on the gasoline power unit featured in the BMW 760i, offering the most advanced and sophisticated highlights in technology, including fully variable VALVETRONIC valve management and variable double-VANOS camshaft control. Further confirmation of the engineering skills of BMW's engine development specialists is borne out by the modifications required for dual-mode drive, with fuel being supplied in the gasoline mode through direct injection and with a hydrogen supply pipe integrated in the engine's intake system.

The key technology is the injection valves required to provide the appropriate fuel/air mixture, blowing exactly the right amount of hydrogen gas into the intake air within fractions of a second.

Burning up to ten times faster than conventional fuel, hydrogen offers a higher level of efficiency. To make use of this potential in full, the V12 power unit in BMW Hydrogen 7 requires particularly flexible engine management ensured ideally by VALVETRONIC and double-VANOS, where both the gas cycle and injection rhythm can be perfectly tailored to the specific features and characteristics of the hydrogen/air mixture.


Minimization of nitric oxides

Under full load the power unit in BMW Hydrogen 7 runs under stochiometric conditions, meaning a complete balance of oxygen and hydrogen (lambda = 1). This mixture ratio also provides the highest level of performance and output on low emissions in the hydrogen mode.

Unlike fossil fuels, the combustion of hydrogen generates neither hydrocarbons (HC) nor carbon monoxide (CO). If at all, minute traces of HC, CO, and CO2 emissions will be generated by the combustion of lubricant and by rinsing the activated carbon filter while running in the hydrogen mode.

The only relevant factor, therefore, is the emission of nitric oxides (NOX) generated above all at particularly high combustion temperatures. Highly flexible combustion management, however, allows an operating strategy able to largely control the formation of NOX. In practice, this means that the engine is run under part load with a high share of oxygen and, accordingly, a high lambda factor of more than 2.

In this case the temperatures in the combustion process are relatively low, keeping NOX emissions to an absolute minimum.

Such a lean burn mode can be maintained throughout a particularly wide range of operation in the engine control map. And since hydrogen offers particularly broad ignition limits and burns at a fast rate, only a small amount of fuel is required in the mixture to generate a high level of efficiency.

To boost engine output, the share of fuel in the fuel/air mixture is also increased in the hydrogen mode.

previous page | go to page 6