A roar fills the small room in MIT’s Building 31 as a car engine, minus the car, revs loudly. Outside the room-one of 12 test cells in the Sloan Automotive Laboratory-a student watches as a computer collects data on the engine, whose spark-plug-free design might one day earn it some room under the hood.

The engine employs a technique called homogeneous charge compress ignition, which gives it a less complicated design than a gasoline engine but the efficiency of a diesel engine. The engine maintains a much higher ratio of air to fuel than an ordinary car’s, heats the mixture through compression, and causes the fuel to ignite spontaneously, without a spark. The result is faster and more efficient combustion and a 10-fold reduction in the amount of pollution the engine emits.

“Here’s a major new idea that has the possibility of having an enormous impact on the industry,” says Professor John Heywood, director of the laboratory. “I’m not going to guarantee it goes into production five or 10 years from now, but it’s on a path to doing that.”

Another novel idea for a more efficient engine uses a device called a plasmatron, invented at the MIT Plasma Science and Fusion Center. The device shoots an arc of electricity through a mixture of air and hydrocarbon fuel, converting it to hydrogen and carbon monoxide. Hydrogen burns much faster than gasoline, and again brings the engine’s efficiency close to that of a diesel engine without running as roughly as diesels do under some conditions.

But while the Sloan Lab looks at these experimental variations on the old internal-combustion engine, its main thrust is to develop a theoretical understanding of how engines work, and then use that understanding to build computer models that designers can turn into better commercial engines.

“People sort of feel that once a technology is developed, it’s developed. But it’s not developed fully,” Heywood says. Engineers can build a working engine without a theoretical understanding of everything that’s happening inside it. But lacking that understanding, they may not come up with the very best engine, he says.

And better engines are a big priority. Improving automobiles’ fuel economy can reduce both U.S. dependence on foreign oil and the amount of carbon dioxide cars pour into the atmosphere, perhaps slowing global warming. At the same time, government emissions standards for other pollutants produced by burning gasoline are becoming stricter and stricter.

Research into more efficient engines is “more lively [now] than I’ve ever known it in my 35 years,” says Heywood. Founded in 1929, the Sloan lab expanded its research, raised more funding, and experienced a surge of interest in the late 1960s, when cars’ contribution to air pollution began to get attention. Research at MIT led to the design of engines with smaller spaces between the piston and the liner, which lowered hydrocarbon emissions. It was in the 1960s that Heywood, then a graduate student studying aerospace propulsion, joined the lab. In 1988, he introduced some of the lab’s results into Internal Combustion Engine Fundamentals, a standard reference for engineers. Now the Sloan Lab is part of the newly formed Laboratory for 21st-Century Energy, in which it joins groups performing basic and applied energy research in other areas.

Industrial partners Ford Motor, DaimlerChrysler, General Motors, ExxonMobil, and Delphi are part of the lab’s Energy and Fuels Research Consortium, which examines such issues as how fuel vaporizes at different temperatures and how unvaporized fuel travels through an engine. The Oil and Lubrication Research Consortium, meanwhile, has funding from other partners to study the role of friction in engine performance.

John DeCicco, a senior fellow with the environmental group Environmental Defense in Washington, DC, says work by the Sloan lab has helped focus the debate over the role automobiles play in producing greenhouse gases. In particular, he cited “On the Road in 2020,” the lab’s 2000 report analyzing a variety of engine and fuel technologies. A follow-up study released this March found that hydrogen fuel cells may not offer any advantage over the improved hybrid engines that should be available by the time fuel cells are ready for market.

“It’s become almost the definitive study,” DeCicco says. “It really was so thorough, and it exercised a very comprehensive methodology. And that just reflects the research and the depth at MIT.”