General Motors first debuted its prototype Homogeneous Charge Compression Ignition (HCCI) engines last summer. Now the company has announced that the powerplant can operate in HCCI mode while idling as well as during part-throttle applications, AutoblogGreen reports. That means that the engine can switch modes on the fly between HCCI and spark ignition more often, which further reduces fuel consumption.

The basic hardware to make HCCI work exists with direct injection, variable valve timing and pressure and temperature sensors in the combustion chamber, the report said. "The key now is to develop the control algorithms to manage the sparkless combustion. The beauty of HCCI is the potential to improve fuel consumption to near-diesel levels without expensive after-treatment systems. HCCI engines can also operate on conventional gasoline or even ethanol." GM is currently testing the engines in a Saturn Aura and an Opel Vectra.