WARREN, MI --- General Motors Corp. officials showcased the HCCI four-cylinder engine May 20 at the company's research and development center, the Detroit News reported. The engine promises up to a 15-percent increase in fuel economy while dramatically reducing NOx gases. 

NOx is a generic term for highly reactive gases that include bonded nitrogen and oxygen, which can cause respiratory problems for people and contribute to acid rain and global warming. 

HCCI stands for homogenous charge compression ignition. 

Uwe Grebe, GM's executive director of powertrain advanced engineering, declined to give a firm date when an HCCI engine would become production ready but said it would be in the next decade. The process can "be applied to many engines, including four- , six- and eight-cylinder engines," Grebe said. 

Paul Najt, GM lab group manager of powertrain systems research, has been studying gasoline compression ignition for 30 years. He said the science behind these engines has moved forward with other engine advances such as direct injection. 

"It's amazing how quickly all of this enabling technology is advancing," Najt said. 

The engine can operate under compression ignition from idle to 3,000 rpm and cruise up to 60 mph. A spark plug also is connected to each cylinder to permit the engine to operate in the traditional mode. But when driving in compression mode, the cylinder's temperature stays cooler. This prevents pollutants from forming, the Detroit News reported. A conventional gas engine ignites its fuel at 3,800 degrees Fahrenheit. When in compression mode, the HCCI engine ignites the same fuel at 2,900 degrees, Najt said. 

Vijay Ramappan, staff engineer for calibration, said the HCCI engine still needs work but will significantly improve city mileage for future cars and trucks.