Toyota Showcases Hydrogen 'Boil-Off' Capture to Improve Powertrain Efficiency

Toyota is exploring a solution to one of the main issues of fuel efficiency facing vehicles using liquid hydrogen fuel.

The automaker, which uses the fuel in its GR Corolla H2 Concept car in the Eneos Super Taikyu racing series, now addresses the problem of hydrogen "boil-off," or vaporized hydrogen, losses.

This happens when the liquefied gas, normally stored at -253 C (-423 F), begins to reach atmospheric temperature in a vehicle’s tank and is lost to the fueling process by dissipating into the atmosphere.

Now Toyota is developing a process to capture the escaping gas and recycle it into either the internal-combustion engine, as in the racing Corolla, or fuel-cell electric powertrain systems.

It is showcasing a concept GR Corolla model to develop the process. Although it is still in the concept stage, if realized, this technology is expected to improve the energy efficiency of the entire liquid hydrogen system by recovering and using boil-off gas as energy.

Toyota is trying to develop technology to produce reusable fuel by sending boil-off gas released from liquid hydrogen in the tank to a self-pressurizer – a device that increases pressure without relying on external energy.

Boil-off gas can then be converted back to usable hydrogen fuel for the engine by applying pressure. However, increasing the pressure sufficiently usually requires energy such as electricity.

Toyota’s self-pressurizer uses the pressure of the boil-off gas to increase pressure by two to four times and produce reusable fuel without using any additional energy.

The concept attempts to capture and then feed the escaping gas into the small fuel-cell package (FC stack) and the hydrogen goes through a chemical reaction to generate electricity.

The electricity generated can be used to power parts like the motor for the liquid hydrogen pump. If realized, it will be possible to supplement electricity equivalent to the amount generated by the alternator or small generator from boil-off gas, boosting energy efficiency.

Boil-off gas that is not used in the electricity-generation process is then converted into water vapor through a catalyst and safely released outside the vehicle.

Toyota says it is actively seeking to form partnerships that will help make this technology fit for commercial on-road use.