8/22/2019 Direct Fuel Injection Defined

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Direct fuel injection defined

Direct fuel injection is a fuel-delivery technology that allows gasoline engines to burnfuel more efficiently, resulting in more power, cleaner emissions, and increased fueleconomy.

How direct fuel injection works

Gasoline engines work by sucking a mixture of gasoline and air into a cylinder,compressing it with a piston, and igniting it with a spark; the resulting explosion drivesthe piston downwards, producing power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder called the intakemanifold. In a direct-injection system, the air and gasoline are not pre-mixed; air comesin via the intake manifold, while the gasoline is injected directly into the cylinder.

Drawing of a direct injection system - - note the injector on the far right at the topof the cylinder

8/22/2019 Direct Fuel Injection Defined

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Advantages of direct fuel injection

Combined with ultra-precise computer management, direct injection allows moreaccurate control over fuel metering (the amount of fuel injected) and injection timing(exactly when the fuel is introduced into the cylinder). The location of the injector also

allows for a more optimal spray pattern that breaks the gasoline up into smallerdroplets. The result is more complete combustion -- in other words, more of the gasolineis burned, which translates to more power and less pollution from each drop of gasoline.

Disadvantages of direct fuel injection

The primary disadvantages of direct injection engines are complexity and cost. Directinjection systems are more expensive to build because their components must be morerugged -- they handle fuel at significantly higher pressures than indirect injectionsystems and the injectors themselves must be able to withstand the heat and pressureof combustion inside the cylinder.

How much more powerful and efficient is direct injection?

Cadillac sells the CTS with both indirect and direct injection versions of its 3.6 liter V6engine. The indirect engine produces 263 horsepower and 253 lb-ft of torque, while thedirect version develops 304 hp and 274 lb-ft. Despite the additional power, EPA fueleconomy estimates for the direct injection engine are 1 MPG higher in the city (18 MPGvs 17 MPG) and equal on the highway. Another advantage: Cadillac's direct injectionengine runs on regular (87 octane) gasoline. Competing cars from Infiniti and Lexus,which use 300 hp V6 engines with indirect injection, require premium fuel.

Renewed interest in direct fuel injection

Direct injection technology has been around since the mid-20th century; however, fewautomakers adopted it for mass-market cars. Electronically-controlled indirect fuelinjection did the job nearly as well at a significantly lower cost, and offered hugeadvantages over the mechanical carburetor, which was the dominant fuel deliverysystem until the 1980s. However, recent developments such as skyrocketing fuel pricesand stricter fuel economy and emissions legislation have led many automakers to begindeveloping direct fuel injection systems. You can expect to see more and more carsmake use of direct injection in the near future.

Diesels and direct fuel injection

Virtually all diesel engines use direct fuel injection. However, because diesels use adifferent process to combust their fuel (gasoline engines compress a mixture of gasolineand air and ignite it with a spark; diesels compress air only, then spray in fuel which isignited by the heat and pressure), their injection systems differ in design and operationfrom gasoline direct fuel injection systems.