High-pressure rotary pump performance in Multijet CR Systems

Shortage of knowledge is still present in the literature on Common Rail (C.R.) about the high-pressure pump performance. Hydraulic-mechanical efficiency of the pump is only known as a mean value and no published data are available on the volumetric efficiency. Due to the fact that part of the pumped fuel can be partially expelled by the pressure-control valve (PCV) and because of the presence of the oil flowing in the cooling and lubrification circuit, the determination of the compression volumetric efficiency seems to be a hard task for PCV integrated pumps. In the present paper a detailed description of the C.R. high-pressure pumps performance has been provided. The dependence of the flow rate, sucked by the C.R. pump, on speed and load has been studied and the characteristic curve of the cooling-lubricant circuit has been determined. A theoretical expression of general application for the volumetric efficiency of reciprocating high-pressure pump has been derived. Furthermore a special procedure was designed and applied for the experimental evaluation of the fuel leakages in PCV integrated pumps. The effective head-capacity curves at different revolution speeds were plotted for different pump types and compared with the electroinjector flow-requirements, so as to allow the evaluation of the efficiency of the pressure-control strategy. An insight into the effect of aging on pump performance was provided. Furthermore the dynamic behavior of the C.R. pump in terms of flow-rate ripple at its delivery was investigated. Finally the pump mechanic-hydraulic efficiency dependence on head and speed was experimentally assessed and analyzed.