Pros and Cons of Direct Injection Engines

Like clothing styles, the notion of reaping benefits from gasoline direct injection engines seems to come and go and come back again. They're alluring to auto engineers for a couple of reasons: the potential savings from fuel efficiency and the potential performance boost, especially if used in concert with a turbocharger. For example, Bosch -- a German supplier of high-tech auto components -- says its gasoline direct injection system cuts fuel consumption by 15 percent and can provide up to 50 percent more low-end torque than a comparable indirect injection system [source: Bosch].

So what's the catch? Well, GDI engines tend to boast clean emissions profiles overall, but they do produce excess oxides of nitrogen, or NOx. Like diesels, they too can spew unsightly and unhealthy particulate matter -- that's environmentalist-speak for "soot" [source: Sawyer]. And for the time being, at least, they cost more to build than ordinary engines. Audi engine development chief Axel Eiser estimated the direct injection engines being put into Audis will cost 5 percent more to build than an ordinary engine. Other estimates say a direct injection engine could cost several hundred dollars more than its indirect counterpart, owing to its more complicated emissions controls [source: Csere].

But as is usually the case with technologies new to the marketplace, developers have been steadily ironing out the problems. The NOx issues have all but disappeared by using a technique called exhaust gas recirculation (EGR). Catalytic converters specifically formulated for GDI engines cut down even further on pollutants [source: Visnic].

With consumer concern about the environment and gasoline prices approaching critical mass, automakers are ramping up production of their GDI offerings and preparing to launch new ones. Move on to the next page to see what automakers have in mind for the future of this reborn technology.