The next advancement in fuel-injection systems is called direct injection and GM recently announced it would expand its use of the feature in 2009. Unlike conventional fuel-injection systems that squirt fuel into the intake tract just upstream of the intake valve, direct injection sprays the fuel into the combustion chamber.
There are two primary benefits to the system. First, there's a cooling effect that occurs when the atomized fuel evaporates in the cylinder, which allows engineers to increase engine efficiency and power via higher compression ratios and more spark advance. Direct-injection systems are also more precise and concentrate fuel around the spark plug, which means less fuel is required to light a cold engine. That reduces the emissions of an engine's dirtiest interval.
Direct injection is certainly not new—VW, Audi, Mazda, BMW, GM and others already sell cars with it—but it is relatively rare because it costs more than port fuel injection. Still, with the fuel economy benefit (between five and 10 percent) and stricter CAFE regulations the feature will likely become more common in the future.
Now, in addition to the turbocharged 2.0-liter four-cylinder and 3.6-liter V6 that already use direct injection, GM will include the feature on a 2.4-liter Four and a 3.0-liter V6. The model lineup that uses these motors includes the 2009 Cadillac CTS and SRX, the Pontiac Solstice, the Chevrolet Equinox and the Traverse, a high-volume mix that will help GM meet ever-tougher fuel-economy targets. —Larry Webster