Click on the HCCI equipped Opel Vectra for a high-res gallery

At the General Motors Proving Ground in Milford, MI on Friday, the company provided their first public presentation of HCCI engines. Most of the major automakers, in addition to researchers at universities around the world have been experimenting with HCCI for much of the last three decades and now it's finally driveable. As part of their 2007 Powertrain technology show, GM brought a Saturn Aura and an Opel Vectra, each equipped with a 2.2L HCCI engine.

Dr. Uwe Grebe gave the assembled media an introduction to HCCI before we got to drive. Ever since Karl Benz's first MotorWagen in 1886, automotive engines have been dominated by the four-stroke cycle which consists of intake, compression, power and exhaust. All four-strokes operate on the same basic principals of opening a valve and drawing in the intake mix as the piston descends and compressing that mixture as it goes back up. The air fuel mixture is then ignited which pushes the piston down as the mixture burns and expands and then the exhaust valve opens as piston goes up and pushes out the exhaust. The ignition part is one of places where things vary.

Read on after the jump to learn how HCCI fits into the process.