These injectors operate within Common Rail systems. They are the most frequently used supply systems of high pressure engines. They enable the separation of high pressure generation function and fuel injection performance. In consequence, they provide flexibility and adaptation of the injection system to the engine higher than conventional systems. Since fuel is located in the chamber with constant high pressure, it is possible to model the injection freely by means of sending electrical impulses to the injectors. A programmer, supplying solenoid valve of the injector with power, activates the sprayer (beginning of injection). After disconnection of the power supply, injection is finished. Injected fuel dose is proportional (with given pressure) until solenoid valve activation; yet, it is not dependent on engine rotational speed or an injection pump. With CR of a new generation, it is possible to perform several injections during single working circulation of a piston. It influences the reduction of fuel consumption, ensures more silent engine operation and lower content of hazardous substances in exhaust fumes.
With Common Rail systems of third generation, piezoelectric injectors have appeared. Their main advantage is a short switching time, approx. 0,1 ms. This is approx. ten times faster than with solenoid injectors. In consequence, the beginning of injection may be freely adjusted as well as fuel dose volume, and multi-phase injection may be performed. Solenoid injectors` inertia has allowed for one initial injection in order to silence combustion noise. Piezoelectric elements group is used as an element controlling the injector operation. Owing to such a fast activation, intervals between injections may be shortened, which facilitates optimisation of engine operation. The amount of fuel, including a small dose of initial injection, is measured very precisely, which is reflected in fuel consumption reduction. In systems equipped with piezoelectric injectors, fuel pressure is increased and it may reach over 2000 bars.