The RENESIS rotary engine, itself a unique feature of the RX-8, is especially suited for the combustion of hydrogen. Whereas in a piston-driven motor, the same cylinder is used for both intake and combustion, a rotary engine has separate intake and combustion chambers, allowing for the elimination of backfiring that can occur when adapting a typical combustion engine to hydrogen.
The separate chamber also allows the more fragile rubber seals surrounding the hydrogen injectors to escape their higher temperatures associated with the burning of the hydrogen. These chambers are also larger than a typical cylinder, and this extra space allows for dual hydrogen injectors.
As hydrogen is less dense than gasoline, the ability to use two injectors instead of one is a significant advantage when it comes to more efficient combustion.
The RX-8 REs produces 206 horsepower when powered by gasoline. This drops to approximately 100 horsepower when hydrogen is used as a fuel. Despite the almost 50 percent power reduction, the RX-8 REs remains very drivable, due to the use of lightweight materials to keep the overall vehicle mass low.
The fact remains, however, that the REs is designed primarily with environmental impact in mind, not performance. Even with a 29 gallon tank for the liquid hydrogen, range is still limited to 62 miles – a far cry from the 341 miles to be found in the 15 gallons of gasoline when running in standard fuel mode.
But as an environmental statement, the RX-8 REs makes a lot of sense.
In addition to producing almost no carbon emissions, many of the interior materials of this sports coupe derived from plant based products. The versatility of being able to easily move from gasoline to hydrogen power and back again is an important design decision, as the infrastructure for hydrogen refueling is still in its infancy around the world.
The REs represents a stepping stone from fossil fuel powered vehicles into the experimental alternative fuel future, and as such, it is a compromise in some ways, but a breakthrough in others.