Sayan Biswas is inventing an unusual kind of green car: one that burns gas.

Biswas's vision is something of an outlier in the green movement. The overwhelming consensus of experts is that fossil-fuel-burning motor vehicles, which account for more than a quarter of the world's greenhouse-gas emissions, must yield to electric vehicles (EVs), and as soon as possible.

But ASAP, it turns out, isn't soon enough. Despite the rapid uptake in EVs in recent years, barely one in seven vehicles on the road in the U.S. is expected to be all-electric by 2035, and only half by 2050. If the world is going to sharply curb vehicle emissions during the decades-long transition to EVs, reducing emissions from standard gas-operated vehicles is essential.

Biswas became fixated on this idea as a graduate student at Purdue University in the early 2010s. After a decade of chipping away at the problem at a government laboratory and then in academia, Biswas has built a gadget the size of a box of cornflakes that he thinks could vastly increase the efficiency of internal combustion engines—so much so that standard gas-burning cars could potentially get 100 miles to the gallon.

Squeezing more efficiency out of internal combustion engines is a difficult challenge. Engineers have been designing and redesigning car engines for more than a century, and in recent years progress has slowed. To Biswas, the problem came down to one thing: a better spark plug.

That's the gist of what Biswas, now a mechanical engineering researcher at the University of Minnesota, and colleagues have developed. Working with researchers at the U.S. Department of Energy's Sandia National Laboratories, they have produced the prototype of a small "plasma igniter" that could replace spark plugs, nudging the fossil fuel in engine cylinders to give up its energy in a much cleaner, more efficient way.

Biswas' prototype, which is about the size of a cereal box, could potentially help tame the gas engine's massive contribution to climate change. "When you use plasma, engines can operate with undetectable levels of emission, and much smaller amounts of gas," he says.

The spark plug, which hasn't changed much in 200 years, is used in all non-diesel vehicle engines to ignite the compressed gasoline-and-air mixture in an engine piston. The result is an explosion of energy released by the burning fuel, powering the vehicle's wheels—or treads or propellers, as the case may be.

Although it takes only a fraction of a second for the spark to ignite fuel, it entails an exceedingly dirty chain of more than 100 chemical reactions that creates several kinds of greenhouse gases and pollutants—not just carbon dioxide, which gets most of the attention, but also nitrous oxide, or NOX, which is 300 times more damaging to the climate, and methane, which is 85 times more damaging.

Igniting gas with plasma instead of a spark changes the entire picture. Plasma is gas made of molecules that have been stripped of one or more electrons, converting the molecules into electrically charged "ions." Because they're electrically charged, ions can change the way surrounding molecules react with one another.

As it turns out, when injected into a fuel-air mixture, plasma ions trigger a chemical chain reaction that's entirely different than the chemical reactions that a spark ignites. The fuel still releases similar amounts of energy, but unlike with conventional fuel burning, the reaction doesn't create any NOX. It also causes the fuel to burn more thoroughly, almost completely eliminating methane. "The fuel chemistry is completely different when you inject plasma," says Biswas.

That may sound too good to be true, but it's based on physics that have been known for decades. Nothing has ever come of it because plasma igniters are typically the size of refrigerators and cost thousands of dollars. The big innovation from Biswas and his fellow researchers involves enlisting electronics and new fabrication techniques to shrink plasma igniters down to reasonable size and cost—Biswas estimates his device would cost about $20 in mass production.

Cars equipped with plasma spark plugs could have a big impact on efforts to tame climate change. But trucks, boats, planes and helicopters may be a bigger opportunity. Unlike cars, all-electric versions of heavier, higher-powered vehicles can't yet match the range of gas or diesel engines at a reasonable cost.

"Moving heavy vehicles like school buses. construction equipment and big trucks to electrification will definitely be slower," says Kate Whitefoot, an associate professor of mechanical engineering and public policy at Carnegie Mellon University who studies transportation. "That's where improving the efficiency of internal combustion engines will be important."

The plasma igniter prototypes developed by Biswas and his colleagues, including researchers at Sandia National Laboratories and the Navy, have been working well in extensive testing, Biswas says. He notes that not only are the igniters ridding test engines of the worst greenhouse gasses, but they're proving more durable than spark plugs, which are prone to fouling and must be replaced periodically. What's more, the plasma igniters enable engines to run efficiently with smaller amounts of gas than traditional spark-plug-ignited engines.

Biswas says he and his colleagues are well-along in discussions with manufacturers to bring the devices to market. "I'm hoping we'll have them in vehicles in five years, but it won't be more than 10 years," says Biswas. The main reason it will take that long, he explains, is mostly due to the challenges of developing new manufacturing processes that can compete with the mass-production efficiency of spark plugs, which has been honed over more than a century. Car manufacturers will have to slightly alter their designs and plants, too.

There are other, less exotic ways of reducing internal-combustion emissions while waiting for the EV revolution to fully take hold, points out Whitefoot. Hybrid electric-gas vehicles can help bridge the gap, she notes, as can newer but more expensive types of synthetic fuels that produce fewer emissions, as well as simply embracing smaller, lighter vehicles that require smaller engines.

But the market has so far proven hesitant to embrace those more conventional strategies. If plasma igniters can offer a breakthrough improvement for tens of dollars and a few turns of a wrench, they may provide the temporary fix we badly need.

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