In a surprising twist on performance and sustainability, Mazda has officially patented a radical six-stroke internal combustion engine that transforms gasoline into hydrogen mid-cycle—offering an intriguing path toward near-zero carbon emissions.
At first glance, the process seems upside-down: after the usual intake-compression-combustion strokes, the fourth stroke does not expel exhaust. Instead, exhaust gases are routed to a specialized “decomposer” where additional fuel is injected.
The decomposer, a catalytic unit built into the engine’s head, separates hydrogen from the hydrocarbons—trapping carbon deposits onboard and storing the liberated hydrogen in a dedicated supply section for reinjection as fuel in later strokes.
This extra pair of strokes—the fifth and sixth—complete the cycle by pulling re-expansion air and finally expelling combustion products. Mazda’s design allows operation in either four-stroke mode (using standard fuel) or six-stroke mode (with hydrogen)—depending on engine conditions. When hydrogen is available, the engine switches into the six-stroke cycle for cleaner operation.
Theoretically, this concept promises near-zero tailpipe carbon emissions, offering a tantalizing hybrid of fossil fuel convenience with hydrogen’s clean-burn properties. Yet, the idea carries inherent complexity: adding a decomposer unit, extra injectors, hydrogen storage, and sophisticated valve control into an already crowded cylinder head adds substantial mechanical and packaging challenges.
Perhaps the most problematic detail is the carbon collection. Since gasoline is primarily carbon, each full tank could generate roughly 82 pounds of carbon that needs to be regularly removed and disposed of during service—a major practical headache.
Although highly innovative, Mazda’s six-stroke concept remains purely theoretical. Without prototypes or performance data, its real-world feasibility—to balance emissions reductions against complexity, cost, and practicality—remains uncertain.
Still, in an era pushing cleaner alternatives, Mazda’s patent reflects the company's willingness to explore bold, unconventional engineering solutions.