Fuel Injection System - Diesel: Operation: Injectors
The injection nozzles inject fuel directly into the pre-combustion (swirl) chamber. Injectors are connected in series with each other with a fuel return line. When fuel from the injection pump reaches 1920 psi (135 kg/cm2 ), needle spring pressure is overcome.
The needle valve is lifted off its seat and allows fuel to enter the cylinder. During this process some fuel lubricates the nozzle between the needle valve and nozzle body.