MAN Truck & Bus
The common-rail system on an internal combustion engine uses an extremely fast solenoid valve in the injector to control the injection process. The armature and valve ball in the solenoid valve move up and open the outlet restrictor when the solenoid is energised. Fuel return when the outlet restrictor is open reduces control chamber compression on the control piston and the nozzle needle opens. The valve spring forces the armature and valve ball back down the solenoid valve and closes the outlet restrictor when the solenoid is not energised.
The injectors inject fuel into the cylinder. These high-pressure injectors finely atomise the fuel when injecting precise quantities into the combustion chamber. They sit in the individual cylinders and are connected to the injection pump via high-pressure pipes. The injectors' length, hole diameter, spray direction and hole shape all influence fuel preparation and thus the engine's output, fuel consumption and pollutant emissions. A fundamental distinction is made between throttle pin nozzles and hole-type nozzles. It is only possible to inject fuel through the nozzle if the fuel pressure is sufficiently high. With in-line and distributor injection pumps this occurs every delivery stroke which generates a high-pressure pulse. With the pump-nozzle unit, pump-line-nozzle and common rail injection systems, the high pressure generated by the pump is only effective while the solenoid valve is operating.