Understanding Direct Gasoline Injection


Ask mature drivers what “under the hood” technology introduced in the past three decades has benefited them the most and you’ll likely hear “fuel injection” mentioned numerous times. That’s because fuel injectors replaced the lowly carburetor, providing a more accurate and dependable air-fuel mixture for modern engines.

Fuel Injection

Fuel injection technology, however, has been around since 1952, when the Robert Bosch Corporation introduced this technology. Gradually, fuel injection found its way to Porsche and other European brands, but it wasn’t until the early 1990s that the last of the carburetors disappeared from American cars. Today, fuel injection reigns supreme, but is now being challenged by a better mousetrap: direct gasoline injection.

Direct gasoline injection improves upon the old technology by utilizing three key components:

  • A high pressure pump
  • A fuel rail
  • Multiple fuel injectors
  • Air Fuel Mixture

With direct gasoline injection engines, the A/F mixture is formed directly in the combustion chamber. Engines run more efficiently with fuel consumption reduced by up to 15 percent and torque improved by up to 5 percent. Unlike traditional fuel injection where fuel takes circuitous route to the combustion chamber, GDI offers an immediate response, eliminating the problem of wasted fuel.

Only combustion air is pulled through the open intake valve during the intake stroke, with high pressure fuel injected by special injectors into the combustion chamber. GDI requires precise calibration to ensure reduced fuel consumption and to achieve the resultant lower levels of emissions that is released into the environment. Car manufacturers are producing new gasoline engines to handle the higher pressures that GDI requires.

Pressurized Gasoline

Robert Bosch is one of the leading manufacturers of direct gasoline injection, with its system utilizing a high-pressure pump that compresses gasoline to the high pressure level required in the fuel rail. The injectors attached to the fuel rail meter and atomize the fuel extremely fast and under high pressure in order to achieve the best possible mixture formation directly in the combustion chamber.

In 2009, Hyundai released its Theta II engine that is designed specifically for GDI. This 2.4-liter four cylinder engine, which also features turbocharging technology, offers a 10 percent fuel economy improvement over a traditional gasoline engine. Moreover, Theta II produces 200 horsepower and offers 186 lb.-ft. of torque.

Theta II has enabled Hyundai to offer a midsize sedan, the Sonata, that offers class leading fuel economy and performance to go along with its segment leading size.

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