Diesel engines hold a lot of promise, especially the ones in use over in Europe. They make more torque than their petrol cousins, usually come equipped with turbochargers, and tend to emit fewer emissions in low-sulfur form.

Researchers at a lab in Munich, Germany, have built a turbocharged diesel engine that they hope will emit less than 5 milligrams of soot and 80 milligrams of nitrogen per kilometer without resorting to a catalytic converter. Lofty goals, but they are making good headway.

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