World's First Driveable HCCI Prototype Hits the Road

Motor, Nov 2007

A Saturn Aura became the world's first driveable vehicle powered by a homogeneous-charge compression-ignition (HCCI) gasoline engine, and it happened at GMs Milford Proving Ground early last month. Power was provided by a production 2.2L Ecotec 4-cylinder powerplant that was modified for a combination of HCCI and conventional spark-ignition operating modes. Aside from the engine and the usual array of dataacquisition devices, the vehicle is a standard Aura.

HCCI is a lean-mixture combustion process that offers a 15% to 20% increase in fuel efficiency when applied to a gasoline engine. In principle, it combines gasoline's inherently low emissions and low-cost aftertreatment equipment with diesels low fuel consumption.

According to the General, sustaining HCCI operation at both very light and high loads has been one of the biggest challenges. For example, during light loads and ultralean air/fuel conditions, the descending piston has a cooling effect that extinguishes the chemical reactions within the combustion gases, causing peak cycle temperatures under 2240°F.

Until practical solutions to these and related challenges are found, GM plans to road-test multimode engines such as the one in the Aura. These are configured to operate in HCCI mode between 1000 and 3000 rpm. Conventional spark-ignition mode is used from start-up to 1000 rpm and then again from 3000 rpm to wide-open throttle.

Matthias Alt, manager of GM's global HCCI program, stated the program is moving ahead "faster than even we ourselves expected," and that his team is developing HCCI to be robust for the global environment. "We're working to make it so that running an HCCI vehicle on any fuel in Florida in the summer is no different than running it in Denver in the winter," he continued.