Unfortunately, things are complicated. An initial idea was to race electric cars with zero emissions and high horsepower. They'd have it all...except for the noise of internal combustion engines fans love.

Also, the evolution of batteries remains insufficient, with two major flaws: too heavy and still take much too long to recharge. All attempts to change those features have failed so far. Formula E (the FIA World Championship for 100% electric single-seaters) rounds are never longer than one hour, so a solution for a 24-hour race remained elusive.

An alternative had to be found, and engineers turned to hydrogen.

The fuel cell

A fuel cell draws in hydrogen as fuel and oxygen from the air as an oxidizer, producing electricity through a chemical reaction with water as the only residue! The electricity produced by the heat pump is then used to power one or even several electric motors. During acceleration, the flow of hydrogen and therefore air are increased accordingly via a turbo pump and reduced by slowing down. But, due to a fairly long response time, a buffer battery is used to provide electricity more quickly and store it during braking (energy regeneration by the electric motor). Hydrogen then provides the electric car with the recharging speed it needs as this happens in about the time it takes to refuel.

However, there are two problems. Firstly, hydrogen gas does not exist naturally and must be produced by chemical reaction or electrolysis, then stored. Secondly, its volume. It has to be stored in tanks sized compatibly with the cars, but that requires compressing the gas up to 700 times the atmospheric pressure in cylindrical tanks in order to withstand said pressure. Only a few kilos of hydrogen can be introduced into the tanks, allowing about an hour of driving time…

To examine the necessary requirements for a prototype capable of competing in the 24 Hours, Green GT, TotalEnergies and the ACO built a car. The prototype executed multiple test sessions, numerous demonstrations and even participated in a few European Le Mans Series races with performances similar to an LMP2. They realised they needed to optimise the dimensions and weight of the heat pump and buffer batteries, the size and position of the tanks, the response times of the power supply assembly produced by the turbopumps, and more.

Hydrogen for the thermal engine?

Fuel cells are not the only option. Other engineers have been working on substituting petrol for hydrogen to power internal combustion engines. The engine must be adapted to take into account the characteristics of hydrogen, i.e. large intake volumes, different cylinder heads, adapted compression systems, etc. This type of combustion engine produces no CO2 unlike traditional petrol engines. Other emissions, like fine particles (-80%) and NOX (-50%), are also at their lowest levels. ORECA, renowned for its LMP2 prototypes, has developed a testing bench for this type of engine, and Ligier recently announced it will produce the JS2 R competition GT equipped with the current V6 engine adapted for the transition to hydrogen. Called the JS2RH2, the car will be at the circuit on 8 June ahead of the 24 Hours Centenary.

In any case, all of these hydrogen techniques will have the opportunity to compete at Le Mans in the future. The ACO will quickly approve these hydrogen cars to take the start, whether equipped with a fuel cell or a hydrogen combustion engine.

On 23 May, ACO President Pierre Fillon announced the creation of a Hydrogen prototype class, approving both types of engines no later than 2026.

PHOTOS (Copyright - ACO/Archives): LE MANS (SARTHE, FRANCE), CIRCUIT DES 24 HEURES, 2019-2022 24 HOURS OF LE MANS. Two generations of the ACO's hydrogen prototype (at the top), on the track in 2019 (in the middle) and in 2022 (above).