Gasoline Direct Injectors GDI

The two most critical differences between a Direct Injection Engine and a standard gasoline engine are how they Deliver Fuel and how the fuel mixes with incoming air. These basic premises make a tremendous difference in an engine’s overall efficiency.

First, the fuel travels via pump from the fuel tank, through the fuel line and into fuel injectors that are mounted into the engine. The Injectors spray gasoline into the air Intake Manifold, where fuel and air mix together into a fine mist. At precisely timed intervals, intake valves open, corresponding to the different cylinders of the engine. As a cylinder’s intake valve opens, a piston in that cylinder descends, sucking the fuel-air mist from the air manifold above into the chamber below. As the piston ascends once more, it squeezes (compresses) the Fuel-Air mix until it is nearly nine times as dense as it was to begin with. Then, that cylinder’s designated spark plug fires, igniting the chamber into a high-pressure, high-energy explosion. This little bang pushes the piston back down with tremendous force, causing it to turn the crankshaft and ultimately send power to the wheels.

With a direct injection engine, however, the fuel gets to skip a step and add a bit of efficiency. Instead of hanging out in the air intake manifold, fuel is squirted directly into the combustion chamber. With an assist from modern engine management computers, the fuel gets burned right where it’s needed, when it’s needed.

Direct Injection Engines literally give you more bang for your buck, for two main reasons. One, they use a “leaner” fuel-air mixture ratio. Second, the way the fuel disperses inside the chamber allows it to burn more efficiently. Let’s take a quick look at each.

The ratio of air to fuel as it burns in an engine will have certain, predictable effects on engine performance, emissions of pollutants and fuel efficiency. When the amount of air in the mixture is high, compared to the amount of fuel, it’s known as a “lean” mixture. When the reverse is the case, it’s called a “rich” fuel mixture.

Direct Injection Engines use a mixture of 40 or more parts air to one part fuel, written as 40:1. That compares to a normal gasoline engine’s mix of 14.7:1. A leaner mixture allows fuel to be burned much more conservatively.

A second efficiency plus for Direct Injection Engines is that they can burn their fuel more completely. The Fuel can be squirted directly where the combustion chamber is hottest — in a gasoline engine that means it ends up close to the spark. With a traditional gasoline engine, the fuel air mixture disperses widely within the chamber, leaving a substantial amount unburned and therefore ineffective.