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 the 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 virtually nothing but vapor in the process.



Development in record time: BMW H2R

The power, performance and the reliability of the engine concept were all impressively proven during the development phase, with the BMW H2R World Speed Record Hydrogen Car showcasing the exceptional potential of this technology. In September 2004, when raced on the high speed track in the French town of Miramas, the BMW H2R broke no less than nine international records for hydrogen drive cars with a combustion engine. The car, powered by a 6.0-litre V12 hydrogen combustion engine, achieved a top speed of more than 300 km/h or 186 mph, setting up new records inter alia for the distance of one kilometre with a flying start and the quarter-mile with a standing start. Acceleration from 0-100 km/h came in just 6 seconds.



Hydrogen tank: compact instead of all-round insulation

The dual-mode drive concept of BMW Hydrogen 7 requires not only a suitable engine management and fuel supply, but also proper integration of two separate fuel tanks: To offer the longest conceivable cruising range, the BMW Hydrogen 7 comes with both a conventional 74-litre (16.3 Imp gal) gasoline tank and an additional fuel tank taking up approximately 8 kilos or 17.6 lb of liquid hydrogen.

This hydrogen tank is a key component of the hydrogen car, with the BMW Group being supported in the implementation of hydrogen technology in the automobile by Magna Steyr as an important partner in development.

The hydrogen tank is made up of a double-wall tank structure consisting of two-millimetre-thick stainless steel plates and featuring a 30-millimetre-thick vacuum super-insulation layer between the inner and outer tank.

This configuration reduces heat transfer to a minimum, the interim layer offering the same insulating effect as approximately 17 metres or 56 feet of styropor. The connection pieces between the inner and outer tanks are made of carbon-fibre bands minimizing the conduction of heat.

The insulation technology developed for the hydrogen tank in the BMW Hydrogen 7 ensures a standard of temperature consistency never seen before in practice. Following a simple analogy to explain the concept - if a tank of this kind were filled, say, with boiling coffee, the coffee would remain hot for more than 80 days before cooling down to a temperature suitable for drinking.

A consistently cold temperature is maintained in exactly the same way with the same supreme effect: Highly effective insulation serves to keep liquid hydrogen at a pressure of 3-5 bar and at a consistent temperature of approximately - 250 degrees Celsius over a long period. The infusion of heat causing hydrogen to evaporate is very small indeed, and any loss of hydrogen resulting from the increase in pressure caused by higher temperatures is controlled with maximum efficiency by boil-off management limiting the inner pressure within the tank and ensuring controlled purge of hydrogen already evaporated.

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