Liquid hydrogen as a transportation fuel

With ever-rising petrol prices and global warming issues, alternative fuels for transportation are high up on the priority list. Hydrogen is already used for this purpose in fuel cell vehicles, but liquid-hydrogen-automobile technology is gradually coming into existence, as BMW is about to launch two liquid-hydrogen-powered cars and cryogenic-hydrogen refuelling technology is being launched. Pros and cons Hydrogen has a density of 0.07 g/cm3, stores 2.6 times more energy per unit mass than petrol but it needs 4 times the volume for a given amount of energy, which is a strong argument in favour of using it in liquid form. Hydrogen is liquefied at cryogenic temperatures and then needs to be isolated in tanks that can add weight and size to a vehicle tank. Hydrogen is also explosive when released in confined spaces such as a garage. Its combustion releases water vapour, which makes it very environmentally friendly, but hydrogen still requires a lot of energy to produce. New liquid hydrogen fuelled cars Contrary to fuel cell conversion, which turns hydrogen into electricity, hydrogen combustion engines require liquefied hydrogen. Refuelling problems make it necessary to devise hybrid engines that can also operate on petrol. Within the framework of its Clean Energy System, BMW is launching two models of liquid-hydrogen-powered cars: - The BWM 750 hl has a hybrid, 12-cylinder combustion engine that can run indefinitely on petrol or hydrogen. Linde is providing the necessary technology to store the fuel at -253°C. The vehicle can achieve a top speed of 190 km/h. The petrol tank has a 600 km range, to which the 900 km range of the hydrogen tank can be added. - The 7 Series, also has a hybrid engine. The 170 l hydrogen tank can keep the hydrogen cold for 70 hours before it vents away. Even though these vehicles are fully-fledged and operational, BMW is only loaning them to selected owners. Both vehicles get electricity from fuel-cell-powered batteries that can operate independently from the engine, thanks to direct hydrogen feed from the tank, enabling accessories such as air-conditioning to operate independently from the engine, at low fuel cost. The refuelling issue For now, one of the drawbacks is the insufficient refuelling network. In order to respond to this need, Linde is launching a self-contained mobile hydrogen refuelling unit in the form of a trailer. The trail H2TM can supply fuel-cell or liquid-hydrogen-combustion cars and carries up to 1000 l of cryogenic liquid. The first mobile hydrogen filling station was put into service in Munich during the football World Cup in 2006. www.bmwworld.com/hydrogen