Gasoline direct injection can improve the efficiency of a gasoline engine by providing greater control of the fuel-air mixture and the combustion processes. The result: better fuel economy and lower emissions.
How it works
Fuel can be injected in precisely the desired location -- generally right next to the spark plug -- to maximize power and keep pollutant emissions to a minimum.
There are two main types of gasoline direct injection -- homogeneous and stratified charge.
Homogeneous gasoline direct injection is the simpler of the two. The fuel-air mixture remains constant throughout. That means a conventional three-way catalyst is all that's needed to treat the exhaust.
A stratified charge system relies on burning a small pocket of rich mixture (more gasoline than air) surrounded by an excess of air. This system is economical on partial loads -- some suppliers claim fuel savings of as much as 20 percent -- but a much richer fuel-air mixture is needed for heavy loads.
Where to find it
Volkswagen Group offers direct-injection gasoline versions of many VW and Audi cars. VW calls the technology FSI, for Fuel Stratified Injection. BMW is set to roll out direct injection across its entire gasoline range in late 2006.
"Our focus is not one or two niche models," BMW spokesman Wieland Bruch said, "but to provide the best available technology over all our model ranges."
The principal drawback is cost, especially for stratified charge systems.
All of the major injection equipment suppliers, including Robert Bosch GmbH, Delphi Corp., Denso Corp. and Siemens VDO Automotive.