The first type to come on the scene was called throttle body injected and where more like a carburetor then the modern fuel injection systems. As emissions standards got tighter car-makers developed Port technology that was much more efficient. Gasoline direct injection takes this to a new level.
GDI is not new technology
To prevent the heat from igniting the fuel in the line these injectors are designed to quickly and completely seal after the fuel is sprayed. They must also be able to spray with pinpoint accuracy at these increased pressures. If this did not happen the fuel would not enter the cylinder or overcome the compression that was building in the combustion chamber.
Advantage of injecting gas direct
Spraying the fuel directly into the cylinder also increases the volumetric efficiency because the intake manifold only delivers air to all cylinders. In the past with multi port, vortec or CPI (central port injected) the air and fuel was mixed in the intake manifold and swirled as it entered the combustion chamber. With GDI it can be injected on demand as needed.
The 1500 pounds per square inch that is used in the direct injection delivery system is similar to the pressures that diesel engines use. Under this massive pressure the fuel charge arrives as a vapor. The injectors release a relatively small perfectly shaped spray of fuel around the sparkplug just before it ignites. This means only the area around the sparkplug has air and fuel to trigger combustion.
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