The Europeans can mess around with urea to clean up diesel emissions, but Honda prefers to keep things simple. The company showed off its clean diesel technology at the 2007 Geneva auto show. This technology gives diesel engines the same emission levels as gasoline engines. To get technical for a minute, the system strips oxides from nitrogen oxide emissions with ammonia. The ammonia is generated inside a catalytic converter through a chemical process, then reabsorbed into the system. OK, enough detail. Honda claims the engines will meet federal emissions standards in the U.S., although the company isn't saying yet whether it will meet California's more stringent standards. Expect to see diesel-powered Hondas in about three years.