A concept model has been developed by Toyota that explores how hydrogen generated while driving can be used to increase the efficiency of liquid hydrogen as an engine fuel.
Liquid hydrogen has a higher density than gaseous hydrogen. Although this means a greater amount can be stored in a tank, it leads to the issue of “boil-off” – where the fuel stored in the tank evaporates due to natural heat entering from the outside. Until now, the boil-off gas has been released into the atmosphere without being used. However, the new concept model shows how the boil-off gas could be used. Although still in the nascent stage, this tech could improve the energy efficiency of the liquid hydrogen system.
Toyota is working to produce reusable fuel by sending boil-off gas to a self-pressurizer – a device that increases pressure without relying on external energy. The boil-off gas can be converted back to hydrogen fuel for the engine by applying pressure. However, increasing the pressure usually requires energy, such as electricity. The self-pressurizer featured in the concept uses the pressure of the boil-off gas to increase pressure by two to four times, sufficient to produce fuel without using additional energy.
During the pressurization process, a certain amount of surplus boil-off gas is still released. This is fed into a small Toyota fuel cell stack where it produces electricity through a chemical reaction. The electricity generated can be used to power components such as the liquid hydrogen pump. Boil-off gas that is not used in the electricity generation process is converted into water vapour through a catalyst and safely released outside the vehicle.
The Japanese company is seeking partners to take on the challenge of developing the technology together. It was showcased at the final round of the 2024 ENEOS Super Taikyu race series in Japan, where the field included a GR Corolla running on liquid hydrogen. Toyota said it will continue to use the world of motorsports to refine its cars and the skills and talents of people, together with its partners, to achieve carbon neutrality.