General Motors and Mercedes-Benz are now both promoting new engine technologies that will provide greater fuel efficiency, according to The Detroit Free Press. GM executives say their new fuel technology may cut fuel consumption by up to 15 percent, and will possibly allow more fuel efficiency than some of its gas-electric hybrids. GM’s new engine transmission system called homogeneous charge compression ignition, or HCCI, combines the high fuel economy of a diesel engine with the comparatively low emissions of a gasoline engine. Mercedes-Benz plans to demonstrate an experimental engine that builds on the concept with three more technologies and greater fuel economy at the Frankfurt auto show in Germany in October. Its concept engine, the DiesAuto, uses an electric hybrid system, a turbocharger and a variable compression ratio in a 1.8 liter four-cylinder engine. Mercedes reports that the engine may generate 238 horsepower and achieve 30 m.p.g. in an S-class luxury sedan on the European test cycle that combines city and highway driving. According to The Detroit Free Press, neither company has revealed when they will begin creating these technologies for production vehicles.