Hydrogen

On the face of it, hydrogen is an ideal fuel for an internal combustion engine. The combustion products contain no carbon dioxide or carbon monoxide – indeed the product of complete combustion should be water. It is alternatively presented as a panacea for road transportation by those who point to emissions, and as being a non-starter by those who point out that the production of hydrogen takes much more energy than can be liberated by its combustion, and the difficulties in producing the infrastructure to make it available to the masses.

The car-makers and various governments are taking hydrogen seriously as a fuel, with some manufacturers supplying limited production cars for road use. One of these, the BMW Hydrogen 7, has a dual-fuel capability that allows it to burn hydrogen and gasoline. Many other car-makers are intent on supplying vehicles with hydrogen fuel cells.

Such developments have not gone unnoticed by those involved in motor racing, and recently an Aston Martin Rapide raced in a 24 Hour GT race at Germany’s famous Nurburgring circuit with a dual-fuel system, allowing the V12 internal combustion engine to burn either gasoline, hydrogen or a mixture of the two. The car in question had a hydrogen storage capacity of 3.2 kg, stored in multiple specially constructed tanks comprising a 15 mm thick aluminium tank with what is described as a composite outer ‘wrapping’, but which is likely to be a filament-wound structure which is typical of many high-pressure vessels used in motorsport.

In terms of energy density, hydrogen’s is high; usually this property is known as the ‘lower heating value’. Where each kilo of gasoline contains around 44 MJ of energy, hydrogen contains almost three times this amount at 120 MJ. However, owing to its low density, hydrogen suffers relative to gasoline on account of its very low ‘volumetric energy density’ – a litre of hydrogen compressed to 700 atmospheres contains around 5.6 MJ of energy, whereas gasoline contains about 36 MJ. Also, the storage pressure being worked to as a provisional standard for automotive applications is 700 bar.

Consequently, to produce a comparable performance, hydrogen needs to be burned at a prodigious rate. The Aston Martin racer stores its hydrogen at 350 bar – about half the usual automotive storage pressure – so its 3.2 kg of hydrogen takes up more volume than it would in a passenger car application. This 3.2 kg contains the same energy as 8.7 kg of gasoline, and so appears quite attractive. However, owing to the very low density of hydrogen, the volume of charge required to enter the cylinders of the race engine required the use of twin turbochargers when using hydrogen alone. The weight penalty of the additional hardware required for the hydrogen-powered racer was about 100 kg, which would present a serious deficit in terms of lap time.

To compete with gasoline, cars will need much more specialised technology if we are to get the vehicle performance we have become accustomed to, even in a passenger car. If hydrogen is to compete with gasoline – even on a dual-fuel basis in racing – it is clear that much needs to be done to decrease the weight penalty of the hydrogen storage, and engines may well need to be boosted, as is the case with the GT Aston.

It is clear then that to replace gasoline, even on a limited scale, there is much that needs to happen, not only in terms of engine technology and on-car storage, but also in terms of fuel production and storage infrastructure. The fact that motorsport is helping to develop the vehicle side of the technology will hopefully advance our learning about how to use hydrogen at a faster rate than the mainstream automotive world can achieve alone.

Fig. 1 - The 3.2 kg of hydrogen stored on the Aston GT car is in four special tanks (Courtesy of Alset Global)

Fig. 2 - The hydrogen-powered Aston GT car in action at the famous Nurburgring circuit (Courtesy of Alset Global)

Written by Wayne Ward