The four-stroke engine has powered cars for more than a century. Intake, compression, power, exhaust. It is simple, steady, and everywhere.
Mazda, however, now wants to change that. The company has filed a U.S. patent for a six-stroke engine. It not only burns gasoline. It breaks the fuel apart, makes hydrogen, and burns that as part of the cycle. The aim is massive yet straightforward: reduce carbon emissions.
The New Strokes
The six-stroke engine begins the same way as any other. Air is pulled into the chamber — the intake stroke. Next comes compression. Then the power stroke. Three strokes the world has long run on.
The change comes with stroke four. This is the re-compression stroke. The exhaust is not pushed out. It is forced through a third valve into a chamber Mazda calls a decomposer. The decomposer works like a catalytic converter but without the costly metals. Just before it, a fuel injector sprays a shot of gasoline into the hot exhaust.
Inside, the heat and the catalyst split the fuel. Carbon clings to the catalyst. Hydrogen is freed. The hydrogen is sent to a small tank. The carbon is trapped in the recovery unit.
Stroke five is re-expansion. The gases are pulled back into the cylinder. Then comes stroke six, the final exhaust. What was once the fourth stroke in every other engine becomes the last in Mazda’s six.
The Hard Part
Thermal cracking is not easy. It requires a temperature between 400 and 800 degrees Celsius (752 and 1,472 degrees Fahrenheit). It needs a catalyst that can survive it. Mazda does not say which one.
Carbon is another problem. A gallon of gasoline carries about five pounds of carbon. Store fifteen gallons, and you have eighty pounds of solid waste. Mazda’s patent allows for a purge system but does not say how often it must be emptied.
One may wonder what happens to the carbon. The patent shows a purge line to clear the decomposer when buildup occurs. Mazda does not say how often it must be emptied. In theory, the carbon is pure and could be used in steel, pigments, or other industries. But that is not part of the plan.
The engine also loses power in six-stroke mode. The patent suggests pairing it with an electric motor to make up the difference. That adds weight, cost, and parts.
The Claims
Mazda claims the system can operate with “no carbon oxides” in the exhaust. That is unproven. Hydrogen burns cleanly, but at high temperatures, it can still produce nitrogen oxides. The patent is silent on this.
No data is given on efficiency. It is unclear whether the energy lost in breaking down gasoline is compensated for by the cleaner burn. The total system, with all its moving parts and heat, may be less efficient than a simple gasoline engine.
The Odds
In 2023, battery electric vehicles accounted for approximately 18 per cent of global sales, according to the International Energy Agency. Gasoline cars still held around 70 per cent. Billions of them remain on the road.
Mazda’s idea is a bridge: use the pumps we have, trap the carbon before it leaves, and burn the hydrogen made inside the car.
The promise is wide. The doubts are wider. No one knows yet if this six-stroke engine can produce enough hydrogen quickly enough, or run strong enough, to matter. What will it cost to build? How will it rate in power? Can it run clean over time, or only in the lab? A patent is not a car. It is an idea drawn on paper, waiting to prove itself in steel. Mazda may have sketched the future, but the road to it is long.
Mazda has a history of odd engines. It kept the rotary alive for decades. It developed Skyactiv-X, a gasoline engine that operates like a diesel, firing on compression.
Now it offers a six-stroke. At a time when the world is building batteries and chasing range, Mazda still plays with pistons and heat.
It may never leave the patent office. It may fail due to heat, weight, or cost. But it shows something else. Mazda is not done with the engine.
And maybe the engine is not done with us.
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