A Radical New Engine Shows Why Internal Combustion Still Matters

Reports of the death of the internal combustion engine have been exaggerated.

Electric vehicles were once poised to diminish the ubiquity of traditional engines, but automakers are booking huge losses and killing off one new model after another.

Sales of new electric vehicles in the US this past quarter were only half what they were at their peak in the third quarter of 2025, according to industry service provider Cox Automotive.

While there’s still an overall trend toward electrification of the world’s light-duty vehicles, gas power is now likely to remain the choice of most consumers for a while—especially in the US where gasoline remains cheaper than in the rest of the world. In defence and aviation, experts say, full electrification may never be an option.

That’s prompted more companies to take a fresh look at old combustion tech, including the rotary engine. They’re also figuring out new ways for gas power and battery power to work together.

A century-old engine, reinvented

Alexander Shkolnik is founder of LiquidPiston, a company attempting a nearly impossible feat: developing a liquid-fuel-powered alternative to the traditional piston engine. 

He says his company has cracked the problem, at least for limited applications.

The key is the rotary engine. Unlike a traditional gasoline or diesel engine, it has no pistons. 

Instead, it has an oddly shaped chunk of metal at its heart, spinning inside an oblong chamber in which the usual cycle of compression, combustion and exhaust takes place. 

LiquidPiston’s engine can run on everything from diesel to jet fuel, while being a fraction of the size of a comparable diesel engine, and up to 30% more efficient than a comparable gasoline one.

Shkolnik and his team didn’t invent this. The first rotary engines were pioneered in the late 1800s by French and American inventors, and made their way into early motorcycles and airplanes. In the 1950s, German engineer Felix Wankel updated the concept to include the spinning triangular rotor. LiquidPiston calls its engine an “inside-out Wankel” to acknowledge the commonalities.

The U.S. Army and Air Force are both watching. Over the past decade, the Defense Department, including its cutting-edge research-funding body Darpa, has pumped tens of millions of dollars into the company. 

Whether LiquidPiston’s engine is up to snuff as a portable power station for front-line troops will become evident by sometime next year. 

That’s when the Army should have results from tests of the latest prototype, says Matthew Willis, director of Fuze, the Army’s new venture-capital-style funding body.

LiquidPiston’s rotary engine is also suited to powering long-range hybrid drones, says Shkolnik. 

The company built and flew a prototype of one such drone, in which batteries power the vertical takeoff and the rotary engine takes over for long-range horizontal flight. 

The company is now working on a second, updated version for the Air Force. The hope is that eventually such a drone could fly farther and run quieter than one powered by a piston engine.

The automaker that won’t give up

Wankel’s engine is legendary among engineers and gearheads, on account of its simplicity and elegance: It has far fewer parts than a typical piston engine. 

While General Motors spent years working fruitlessly to develop rotary engines, Mazda’s efforts made it to the showroom floor. 

In 1967 the company released the Cosmo Sport 110S, a car legendary for its styling if not its reliability. Others, including France’s Citroën, dabbled in rotary.

The rotary engine’s last U.S. appearance was in the 2012 Mazda RX-8 sports car. The vehicle was beloved for the sound of its race-car-like engine, but its dirty emissions ultimately doomed it—a chronic Wankel problem.

Mazda never gave up completely. In 2024, the company reconstituted its rotary engine research group. 

In 2025, the company unveiled a truly odd duck: the 510-horsepower plug-in hybrid Vision X-Coupe concept car with 100 miles of electric-only range, and up to 500 miles total with the car’s rotary gas engine engaged.

In the X-Coupe, the vehicle’s shaft is directly driven by a Wankel. “This direct propulsion delivers an evolved ‘joy of driving’ with significant range,” says a company spokeswoman.

Translation: This is no Prius, but part of a new breed of plug-in hybrid supercars. (See also: Ferrari)

A strange new hybrid

A new kind of hybrid could be a bridge technology to EVs, says James Turner, a professor of mechanical engineering at King Abdullah University of Science and Technology in Saudi Arabia.

Instead of battery-powered electric motors working to support the gas powertrain, as in many contemporary hybrids, the gas motor serves as a generator to charge the electric powertrain’s battery. 

That’s why they’re called extended-range electric vehicles, aka EREVs. Nissan has said it would release an EREV version of its bestselling Rogue next year.

LiquidPiston’s Shkolnik says that someday, his company’s novel rotary engine could be ideal for providing range extension.

For the foreseeable future, the right answer will be the current style of hybrid with a traditional engine, says James Heywood, who literally wrote the textbook on modern internal combustion engines. 

If every new car was a hybrid, the U.S. could increase gas vehicle efficiency by 30% while raising the sticker price by a single digit percentage, he says.

Hybrid, plug-in hybrid and EREV tech works regardless of the engine style, and regardless of whether that vehicle drives, flies or swims. 

The entire world’s personal-vehicle fleet will eventually be almost entirely electric, says Turner. 

But on the way there, the gas-powered combustion engines will play an invaluable, if supporting, role.