GM engineers are doing road-tests of a new internal combustion engine design, which the carmaker claims uses 15% less fuel than conventional petrol engines. A Saturn Aura and Opel Vectra have been fitted with new homogeneous charge compression ignition (HCCI) powerplants, and also feature direct injection, electric cam phasing, variable valve lift and cylinder pressure sensing technologies to help minimize fuel consumption.

The technology has been around for more than thirty years but only recently have research groups started trailing working prototypes. Its proponents claim the petrol engines offer the fuel efficiency of diesel but with the cleaner exhaust gases of the petrol. The efficiency comes from burning fuel at lower temperatures and reducing the heat energy lost during the combustion process. Consequently, less carbon dioxide is released because the vehicle’s operation in HCCI mode is more efficient.

An HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder. Unlike a spark ignition gas engine or diesel engine, HCCI produces a low-temperature, flameless release of energy throughout the entire combustion chamber. All of the fuel in the chamber is burned simultaneously. This produces power similar to today’s conventional gas engines, but uses less fuel to do it. Click here to read up more on the HCCI technology.