BMW Hydrogen 7 - production-ready, hydrogen-gasoline V12 Saloon

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.

With hydrogen, contrary to fossil fuel, not containing any carbon, 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. This, in turn, means an increase in combustion temperatures under higher load. With the fuel/air mixture range creating the maximum amount of nitric oxide lying between lambda = 1 and lambda = 2, the engine management of BMW Hydrogen 7 cancels out this operating range with its negative effects on emission management without any reduction or change in torque.

NOX emissions are almost completely avoided under full load with a lambda factor of 1. To convert the minimum amounts of NOX still remaining under these operating conditions, all the engine needs is a regular three-way catalyst system, the specific composition of exhaust gases in a hydrogen combustion engine running under stochiometric conditions (lambda = 1) promoting the conversion of nitric oxides possibly contained in the exhaust emissions by way of the three-way catalyst. In practice, therefore, the drive unit featured in BMW Hydrogen 7 offers the same dynamic performance in the hydrogen mode as when running on gasoline, while emitting nothing but vapour in the process.

Development in record time: BMW H2R

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