The U.S. imports about 10 million barrels of oil daily, much of it from politically volatile regions. MIT’s Daniel Cohn and John Heywood are working on innovations in the traditional car engine that, if widely adopted, could cut that total by about 20 percent.
One key to their goal of exploiting the full potential of the gasoline-powered spark-ignition engine – the engine that powers most U.S. cars and many trucks – is a device called a plasmatron.
This device’s core element is a plasma. Plasmas are electrically charged gases, and they’re everywhere – from the interior of neon light bulbs to the upper atmospheric displays called the Northern Lights.
In this case, the plasma’s role would be to promote the conversion of some of a car’s gasoline to hydrogen. The concept of using plasma technology in this way isn’t new: a Washington state firm is making plasma furnaces, based partly on MIT Plasma Science and Fusion Center (PSFC) research, that turn organic materials like industrial or medical wastes into energy. “Plasmas can convert almost any type of organic material into hydrogen,” notes Cohn, a PSFC senior research scientist and head of the center’s Plasma Technology Division.
But the researchers want to take the concept a big step further, using plasma technology to turn cars into small-scale hydrogen- producing plants – and sharply boosting the spark-ignition engine’s efficiency along the way.
“Spark-ignition engines are roughly 30 percent efficient and diesels are about 40 percent efficient,” notes Cohn. “We want to approach a diesel level of efficiency while avoiding diesel’s pollution problems.”
The plasmatron – about the size of a half-gallon milk carton – would convert about a third of a vehicle’s gasoline stream into hydrogen. In doing so, it would boost efficiency in varied ways.
The gasoline-hydrogen-air mixture, for one, burns faster and more completely than a standard one. Adding hydrogen also permits a big boost in the ratio of air to fuel in an engine’s cylinders – a phenomenon called “lean burn.”
Why does that matter? For one thing, lean burn itself both cuts pollution and boosts efficiency. In addition, hydrogenenabled lean burn can let you combine two energy-saving techniques that right now can’t easily be used together in an engine. One such technique is turbocharging. Turbocharging boosts the amount of fuelair mix injected into an engine’s cylinder. That in turn increases the amount of power the engine produces.
The second is a high compression ratio – the ratio between the cylinder’s volume when the piston is all the way down, and when it’s all the way up. High compression ratios, too, push up an engine’s power output. But currently, notes Cohn, “you can’t readily have a high compression ratio in a turbocharged engine, because you’ll generally get engine knock.” But if you use a lean gasoline-hydrogen-air mixture, there’s no knocking.
Heywood, a mechanical engineering professor and head of the Sloan Automotive Laboratory, is working on these and other ways to optimize engine performance. But the researchers are trying to commercialize the system, too. They have an industrial partner, and hope their engine can be road-tested in cars within a year or two.
And will the ultimate result be to boost the efficiency of spark-ignition engines by a quarter or more? “I think there’s a good chance we’ll get there,” says Cohn.