Injection nozzles for diesel engines feed the fuel into the combustion chamber, vaporize the fuel, shape the injection process and seal the combustion chamber. They consist of the nozzle body or nozzle-holder assembly and the nozzle needle.
The nozzle-holder assembly provides pressure-proof mounting in the cylinder head and contains one or two pressure springs as well as other components for adjusting the injection pressure. The nozzle needle is a tapering pin which is pressed into its seat by the spring. If the fuel pressure is greater than the force of the spring, the needle is pressed upwards and fuel is injected through the openings in the nozzle. When pressure drops, the nozzle closes once again.
The injector receives control impulses from the EDC to open and close the nozzle needle. Short lines connect the injectors to the rail (high-pressure connection). Modern, fast-switching solenoid-valve injectors in commercial vehicles can produce as many as five injections per working cycle. These are composed of up to two pilot injections, the main injection and two post injections. The pilot injections produce a softer combustion process. The annoying "hammering" of a diesel started cold thus now belongs to the past. Post injection improves the combustion of soot particles and thus considerably reduces the generation of fine dust.
Commercial vehicles mainly employ blind-hole nozzles. After injection, small residual volume of fuel is retained in the so-called blind hole below the nozzle needle. When this vol-ume of fuel evaporates, emissions of hydro-carbons (HC) increase. So the amount must be kept as small as possible. This is offset by the advantage of great design freedom in the number of holes, length of hole and spray dis-persal angle. This applies, in particular, to nozzles with a cylindrical blind hole and a round nozzle cone. One alternative is a nozzle with a conical blind hole. Here the volume of pollutant is smaller.