Pure hydrogen is highly flammable and produces a great deal of energy when it reacts with oxygen, so safety is of primary importance in the design of any hydrogen-powered vehicle. The H2R's fuel tank is vacuum-insulated and double-walled, and it's equipped with three active safety valves.
To prevent possible leaks in the jacket around the fuel tank, which helps maintain the liquid hydrogen at a sufficiently low temperature (hydrogen takes its liquid form at -423F/-253C), the H2R features a double-redundant safety system: If the pressure within the tank ever exceeds 5 bar, two additional safety valves open up immediately. As an additional safety precaution, the combustion chambers are cooled by air before the hydrogen/air mixture flows into the cylinders to ensure that it won't ignite in an uncontrolled manner.
Refueling the H2R
Aside from the notable scarcity of hydrogen filling stations, refueling a hydrogen-powered vehicle requires no more effort than refueling a gasoline-powered one.
Hydrogen is added to the H2R's tank at a mobile hydrogen filling station through a manual tank coupling. Because of an interesting safety setup, it is impossible for hydrogen gas to leak into the air during the refueling process. In a liquid-hydrogen-powered BMW, the hydrogen left in the tank has returned to a gaseous state by the time the driver needs more fuel. This gaseous hydrogen exerts a higher pressure inside the tank. At the refueling station, when super-cold liquid hydrogen is pumped into the tank, the gaseous hydrogen already there condenses. The condensation of the gaseous hydrogen reduces the partial pressure inside the tank, so no hydrogen escapes while the tank is being filled.
In the next section, we'll see how the H2R engine turns hydrogen into energy.