Gaseous hydrogen able to escape in this way is diluted in a venturi pipe and oxidated in a catalyst to form vapour. The period in which a half-full hydrogen tank will be emptied completely in a controlled process is about 9 days, and even then the car is still able to cover approximately 20 kilometres or 12 miles in the hydrogen mode with the fuel remaining in the tank.

Defined conversion of liquid into gaseous hydrogen forms a permanent, ongoing process whilst driving: hydrogen is removed from the tank in gaseous condition and fed to the fuel mixing and supply system. For this reason liquid hydrogen is evaporated in a specific, controlled process within the tank, building up a gas "cushion" under defined pressure.

Gaseous hydrogen extracted from the tank uses heat from the engine's coolant circuit to be warmed up for the subsequent fuel mixing process. This heat is generated by a system of two interacting heat exchangers. The heat exchanger in the so-called secondary system capsule (SSC) receives its heat from the engine's cooling circuit and delivers this heat, first, via the second heat exchanger to the hydrogen tank and, second, to the hydrogen itself warmed up for the subsequent fuel mixing process.



Filling the tank in a process standardized worldwide

After manually connecting the tank pump coupling, the hydrogen tank is filled up automatically without any intervention on the part of the driver. So all the driver has to do is open the tank filler flap by pressing a button in the cockpit. Then he connects the tank filling coupling to the fuel tank cap simply by interlinking the two components with one another, the subsequent process of filling up the tank being completed automatically in about eight minutes.

BMW's engineers have developed a standardized tank coupling for all liquid hydrogen filling stations worldwide. This tank filler has been engineered in close cooperation between car makers, fuel supply companies, and the German company Linde with the technical know-how required for the generation, distribution and use of hydrogen.

The European automotive industry was represented in this joint development by the BMW Group, ensuring a worldwide technical standard for liquid hydrogen filling systems.

The driver can check the fuel level and the remaining range on both fuel systems simply by pressing a button in the direction indicator lever, the levels measured then being shown in the cockpit display beneath the speedometer.

The driver is able to switch from hydrogen to gasoline manually by way of a separate button in the multifunction steering wheel - and with both engine power and torque remaining exactly the same regardless of the mode of operation. Switching over from one mode to another has no effect on the driving behaviour and performance of the BMW Hydrogen 7.

While driving in the hydrogen mode, the display presents not the outside temperature and the time of day, but rather the chemical symbol for molecular hydrogen: H2, thus showing the driver quite clearly that the car is currently running on hydrogen fuel.

The operation control system in the BMW Hydrogen 7 gives priority to the use of hydrogen, with the engine always starting in the hydrogen mode in order to minimise CO and HC emissions during the warm-up phase until the catalyst has reached its normal operating temperature.

This configuration serves to further improve exhaust emissions to an even higher standard. And should one of the two types of fuel be fully consumed, the system will automatically switch over to the other type of fuel in the interest of securing an ongoing supply.

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