Mazda Readies Japan’s First Diesel Model in U.S.

This autumn Mazda Motor Corp. will become the first Japanese carmaker to offer a clean-diesel option when its Mazda6 sedan adds a twin-turbocharged oil burner to its engine lineup.

The Skyactiv-D 2.2-liter diesel operates with a compression ratio of only 14.0:1, which Mazda describes as the lowest ever for a mass-production diesel. The lower ratio delays combustion by half a millisecond enough to promote better air-fuel mixing, lower combustion temperatures and less oxides of nitrogen in the exhaust stream, according to the company. The resulting efficiency eliminates the need for an aftertreatment emission control system.

The lower compression ratio also permits an aluminum block and lighter pistons and crankshaft. Mazda says the engine is 10% lighter and 20% more fuel efficient than a conventional diesel with similar output.

The relatively high-revving engine has a redline of 5,200 rpm compared with about 4,500 rpm for most diesels.

Mazda hasn't announced specs for the American-market variant of the diesel, but the European version is rated at 173 hp and 310 lb-ft of torque. Media reports say the engine will achieve a U.S. Environmental Protection Agency highway fuel economy rating of 44 mpg.

The standard 2.5-liter 4-cylinder gasoline engine in the 2013 Mazda6 makes 184 hp and 185 lb-ft of torque and is rated at 38 mpg on the highway. The company stopped offering a V-6 gasoline engine for the car when the 2013 model year began.