The C&D article helped explain it a lot.

However, HCCI still doesn't sound like anything worth pursuing. Unless Honda has found a breakthrough to this, the difficulty of running a HCCI engine, along with having to "hybrid" it with Internal Combustion components when the car isn't running lean, and then pairing this system up to an electric motor just seems overly complex.

Also, since octane is a measure of resistance to combustion under pressure, which seems to fly in the face of what HCCI tries to do, would a HCCI engine perform better on lower octane gas?

Hey, and thanks for explaining this guys.