An innovative, efficient, and robust algorithm is presented for the evaluation of the instantaneous flow-rate in high-pressure liquid flow pipelines. This algorithm is based on the pressure time histories measured at two locations. A simple ordinary differential equation has been derived from the mass and momentum conservation laws and has been solved analytically. This equation allows the flow-rate time fluctuations to be evaluated accurately around their mean value, without any need for initial datum on the liquid flow velocity. A measuring device has been designed and realized to evaluate the flow-rate. The proposed flowmeter layout consists of a piece of pipeline endowed with two piezoresistive pressure sensors equipped with miniaturized thermocouples, the pressure sensor conditioners and a central processing unit (CPU), in which the algorithm for the evaluation of the flow-rate has been implemented. A more sophisticated version of the flowmeter algorithm, which includes unsteady friction in the flow-rate evaluation, has also been developed. Different algorithm versions have been assessed and successfully validated through a comparison with numerical flow-rate data predicted using a reliable one-dimensional model of a common rail (CR) fuel injection system. The prototypal flowmeter has been installed at the delivery section of a CR volumetric pump in order to investigate the flow-rate ripple. The flowmeter traces have been compared with the predictions of a previously developed theoretical model for the pump delivered instantaneous flow-rate, in order to further assess the reliability of both the model and the flowmeter as well as to have a better understanding of the cause and effect relationships between the flow-rate time history and the dynamic working of the pump. The effects that the actuation of the fuel metering valve (FMV), which is placed at the CR pump inlet, has on the instantaneous delivered flow-rate have also been analyzed.
The flow ripple in an internal gear pump was measured by means of a new instantaneous high-pressure flowmeter. The flowmeter consists of two pressure sensors mounted on a piece of the straight steel pump delivery line, and a variable-diameter orifice was installed along such a line, downstream of the flowmeter, to generate a variable load. Three distinct configurations of the high-pressure flowmeter, characterized by a different distance between the pressure transducers, were analyzed. Furthermore, a comprehensive fluid dynamic 3D model of the pump and of its high-pressure delivery line was developed and validated in terms of both the delivery pressure and the flow ripple for different pump working conditions. For the three examined configurations of the flowmeter, the measured flowrate time histories matched the corresponding numerical distributions at the various operating points. Finally, the validated 3D model was applied to predict the incomplete filling working of the interteeth chambers, and the obtained numerical pressure time histories along the delivery line were used, as input data, to assess the reliability of the flowmeter algorithm even in these severe operating conditions.
A new-generation common feeding (CF) fuel injection system without rail has been compared with the standard common rail (CR) apparatus for diesel engine passenger cars. The high-pressure pump in the CF apparatus is connected directly to the injectors, and a volume of about 2.5 cm3 is integrated at the pump delivery. Experimental tests on solenoid injectors have been carried out for the CF and CR apparatus at a hydraulic test rig. The dependence of the injected volumes and total injector leakages on the energizing time (ET) of the two systems has been investigated for different rail pressure levels. Furthermore, the measured injected flow-rates of the CF and CR systems have been compared for single and pilot–main injection events. In general, the injection performance of the two systems is very similar, even though the differences occur in the high-pressure transients. The dynamics of the pressure waves changes because the high-pressure hydraulic layouts of the two systems are different, and the propagation and reflection of the rarefaction waves, triggered by the injection events, occur in different ways. A previously developed one-dimensional (1D) code for the CF high-pressure layout has been further validated by means of a comparison with the experimental data. The effects of either a calibrated orifice installed at the pump delivery or an injector-integrated Minirail on the CF performance have been investigated by means of the model. Numerical parametrical tests have also been conducted on the pump-to-injector pipe length. The additional orifices that can be installed in the high-pressure circuit of the CF are effective, provided their diameter is smaller than the diameter of any other orifice inserted in the injector. Furthermore, the presence of a Minirail within the injector has an impact on the injected flow-rates of small injections, such as pilot, pre, after, and post, and also induces a reduction in the energy stored in the pressure waves. Another relevant active damping strategy of the pressure waves for the CF involves shortening the pump-to-injector pipe as much as possible. Finally, the fluid dynamical transients within the solenoid injector have been discussed for the CF and CR systems. The numerical time distributions of the main variables within the injector are shown to be independent of the presence of the rail in the layout.
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