Around 400 meters from the buzz of the paddock during this year’s 24 Hours of Le Mans stood a tent with two racing cars and a mobile fueling station. Every now and then, people wearing blue T-shirts bearing the logo of “Mission H24” would walk by the cars to attend meetings in a motor home sitting next to the tent.

One of those people was François Granet of the Franco-Swiss company GreenGT. He appeared particularly thrilled because, on the eve of the start of this year’s race, the ACO (Automobile Club de l’Ouest), which organizes the 24 Hours of Le Mans, announced a new category of race cars at the Le Mans event for 2025: hydrogen-electric prototypes. The company’s forerunners were stationed in that tent.

Creating a category

GreenGT is developing the hydrogen fuel cell powertrain for these cars, which will be designed around a chassis built by Oreca and Red Bull Technologies. “In partnership with ACO, we are helping define the sporting and technical regulations for the new category,” Granet said.

The H24 car, the latest of the two prototypes, is being tested at different circuits across Europe. It ran some tests at Le Mans on the days leading up to this year’s race and did a demonstration lap of the 13.6 km (8.5 mile) circuit just before the start on Saturday afternoon. “The data from these tests help us to understand and improve the car’s performance, which forms the basis of creating the regulations for the new category,” he said.

One of the drivers who tested the H24 during the weekend was Stéphane Richelmi, a past winner at Le Mans. Richelmi, who won the 24-hour race in the LMP2 class in 2016, said he was most impressed with the hydrogen engine’s power. “Since it’s a new technology and doesn’t use either petrol or diesel, I was expecting the car to have low torque and a low top speed,” he said. “But it delivered more torque than a petrol engine, and even without pushing too hard, the car easily reached 280 km/hr [174 mph] on the straights.”

The 32-year-old from Monaco said driving the car for the first time felt a bit strange. “It reminded me of my karting days,” he said. “There is the engine, brakes, acceleration pedal, and steering wheel—but no gearbox, which normally is a big part of a racing car.”

The H24 is powered purely by electricity. The fuel cell stacks use hydrogen and oxygen to produce electricity, most of which is directly fed into the motor. But a part is fed into the battery, which is used for faster acceleration, such as when a car is exiting a corner.

Test runs

According to Richelmi, his role is to “feel” the car on the track and give this information to the engineers. “The engineers see many things with data and simulation,” he said. But as a driver, you get a real feel of the car. My role is to tell engineers that, in certain cases, while things may look good on the computers, it may not be good on the track.”

The powertrain makes a high-pitched buzz, and Richelmi said drivers can hear more of the car. During the tests, the car was filled with high-pressure hydrogen at a fueling station developed by TotalEnergies. “While we kept the pressure at 400 bars for the tests, the tanks can hold hydrogen up to 700 bars. The higher pressure means there is more hydrogen volume, which means more autonomy,” Granet explained. For a single lap of the Le Mans circuit, the car used 800 g of hydrogen.

Although the tests have been encouraging, there are many hurdles to clear before the car becomes ready for racing in terms of speed and endurance. The first of these challenges is weight reduction. “At 1,400 kg, the H24 still weighs 450 kg more than a LMP3 car and 155 kg more than a GT3 car. But since it’s a raw prototype, we can work on every single part to try to reduce weight,” Granet said.

For GreenGT, the H24 project has a symbiotic relationship with the hydrogen trucks the company has developed for heavy industry. The 44-tonne (48.5 ton) trucks will be able to travel 450 km (280 miles) on a single fill-up. “We bring technologies from trucks to the racing car and vice versa,” Granet said. “Though the objectives of a racing car and a truck are different, there are many similarities, starting with the powertrain technology. Interestingly, the power output of the engines for H24 and our trucks is somewhat similar.”

According to Granet, optimizing power and consuming less hydrogen are key, and they might benefit from things like optimizing the humidification of air when oxygen enters the fuel cell. This sort of adjustment is common to both the projects.

Granet also argued for the benefits of using hydrogen powertrains. “An electric engine is far more efficient than a normal aspirated four-stroke engine. More importantly, it is clean energy, as it emits just water vapor. Moreover, we are also targeting the use of only green hydrogen that is produced from nonpolluting sources,” he said.

Dhananjay Khadilkar is a journalist based in Paris.

https://arstechnica.com/?p=1795573