Fuel Injector: Description and Operation

Fig. 7 Fuel Injector:

The injection valves inject the fuel allocated by the fuel distributor into the intake ports directly in front of the cylinder intake valves. The injection valves are secured in a special holder in order to insulate them from engine heat. This insulation prevents vapor bubbles forming in the fuel injection lines which would lead to poor starting behavior when the engine is hot.

The injection valves have no metering function. They open of their own accord when the valve opening pressure is exceeded. They are fitted with a valve needle which vibrates (chatters) audibly at high frequency when fuel is being injected. This results in excellent fuel atomization, even with the smallest of injected quantities. When the engine is switched off, the injection valves close tightly as soon as the fuel-system pressure drops below their opening pressure. This means that no more fuel can enter the intake ports once the engine has been shut down.

Fig. 15 Fuel Injector with Air Shrouding:

The injectors also incorporate "Air Shrouding". The air-shrouding principle is based upon the fact that a portion of the air drawn in by the engine enters around the fuel-injection valves with the result that the fuel is especially well atomized at the point of exit.

Without Air Shrouding:

With Air Shrouding:

As a result of the improved atomization lower fuel consumption and levels of emissions are realized.