BMW Sets Speed Records with Hydrogen fuelled V12

The VALVETRONIC variable valve timing on the 12 cylinder offered an ideal tool for controlling this demanding gas charge cycle. VALVETRONIC controls not only the duration of valve movement, but also the actual valve lift.

This effect is provided by an intermediate lever between the camshaft and the two intake valves on each cylinder infinitely modified in its position relative to the camshaft by an additional eccentric shaft operated by an electric motor.

Depending on the position of this eccentric shaft, the lever transforms the "hump" on the cams into a larger or smaller valve movement.

VALVETRONIC is based consistently on BMW's infinite camshaft adjustment process. Already well-known under its trade name VANOS, this system is an integral part of the VALVETRONIC concept. Incorporating a hydraulically controlled adjuster unit in the camshaft drive, VANOS modifies the beginning and end of the valve opening period, fully variable valve management serving to adjust the gas charge cycle in the 12 cylinder power unit perfectly to the requirements and characteristics of hydrogen drive.

With hydrogen being injected into the intake manifold as late as possible, the injection valves have to meet very demanding requirements. Hence, the valves are a trendsetting new development for BMW. And since gaseous hydrogen takes up a larger volume per unit of energy than liquid gasoline, the hydrogen injection valves are larger than conventional injection valve units.

A further point is that the valves have to cover a far wider range of different features and requirements, operating under all kinds of system pressure levels and with injection periods ranging from very short to relatively long. One of the main objectives in developing the valves was to inject exactly the right amount of hydrogen required into the intake manifold within a very short time-frame at very high engine speeds and under full load.

Under full load the 12 cylinder power unit runs on a fuel/air mixture of lambda = 1. This is exactly the same mixture we also find on a state-of-the-art gasoline engine, the mixture which, in principle, offers the highest and most efficient power output in a combustion engine. Under part load - again a significant benefit offered by hydrogen - the engine runs efficiently in the lean burn mode with surplus air.

Under specific conditions, that is with a specific fuel/air mixture, the combustion of hydrogen leads to the generation of nitric oxides. This mixture "slot" starts slightly above lambda = 1 and extends to the range of lambda > 2.

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