General Motors Corp. said it is testing a combustion process in concept cars that could raise fuel economy by 15% over current conventional engines, The Associated Press reported. The process GM and other automakers are testing, called homogeneous charge compression ignition, approaches the fuel efficiency of a diesel engine without the need for advanced pollution controls, GM said in a statement. It is being tested in two drivable concept vehicles, a Saturn Aura and an Opel Vectra, and was shown to reporters late last month at GM's proving ground in Milford, Mich. The process ignites an air-fuel mixture in the cylinders by compressing it, producing a low-temperature, flameless energy release in the combustion chamber, the company said. Since all the fuel in the combustion chamber is burned more quickly than conventional spark-ignition engines, the engine uses less fuel to produce power that is similar to conventional engines, AP said. GM estimates the technology is six or seven years away from showrooms, mainly because it still needs to work on controlling the combustion process, AP reported. L&MT
