ANALYSIS OF REALIZATION OF STEPPED FUEL INJECTION WITHOUT CHANGING DESIGN OF COMMON RAIL INJECTOR

A calculated-experimental analysis of realization of stepped front edge of injection rate (stepped injection) was carried out. Common rail injectors (CRI) of three most widely used designs took part in the research: CRI No 1 distinguished by its control valve with a locking cone and piston; CRI No 2 with a control valve unloaded from fuel pressure, channel on the piston and enlarged internal volume; CRI No 3 with a control valve having a flat lock and a needle which is not closing the drain channel when staying in the upper position. It is demonstrated that friction in the couple – control valve piston/guiding surface of the CRI No 1 hampers realization of stepped front edge of injection rate due to its smoothening. When using the CRI No 2, it is possible to obtain stepped injection only at low fuel pressure in common rail (pcr ≤ 50 MPa). The CRI No 3 ensure the stepped injection at different pressures up to pcr=200 MPa.