Development and Application of a Complete Multijet Common-Rail Injection-System Mathematical Model for Hydrodynamic Analysis and Diagnostics

Abstract

A rather complete mathematical model for a common-rail injection-system dynamics numerical simulation was developed to support experimentation, layout, and control design, as well as performance optimization. The thermofluid dynamics of the hydraulic-system components, including rail, connecting pipes, and injectors was modeled in conjunction with the solenoid-circuit electromagnetics and the mechanics of mobile elements. One-dimensional flow equations in conservation form were used to simulate wave propagation phenomena throughout the high-pressure connecting pipes, including the feeding pipe of the injector nozzle. In order to simulate the temperature variations due to the fuel compressibility, the energy equation was used in addition to mass conservation and momentum balance equations. Besides, the possible cavitation phenomenon effects on the mass flow rate through the injector bleed orifice and the nozzle holes were taken into account. A simple model of the electromagnetic driving circuit was used to predict the temporal distribution of the force acting on the pilot-valve anchor. It was based on the experimental time histories of the current through the solenoid and of the associated voltage that is provided by the electronic control unit to the solenoid. The numerical code was validated through the comparison of the prediction results with experimental data, that is, pressure, injected flow rate, and needle lift time histories, taken on a high performance test bench Moehwald-Bosch MEP2000-CA4000. The novel injection-system mathematical model was applied to the analysis of transient flows through the hydraulic circuit of a commercial multijet second-generation common-rail system, paying specific attention to the wave propagation phenomena, to their dependence on solenoid energizing time and rail pressure, as well as to their effects on system performance. In particular, an insight was also given into the model capability of accurately predicting the wave dynamics effects on the rate and mass of fuel injected when the dwell time between two consecutive injections is varied.

The new-generation of solenoid injectors equipped with pressure-balanced pilot valves for energy saving and dynamic response improvement

“…The electromagnetic force F m can be expressed by measuring both the voltage (V) and the electric current (I) time histories and using the following formulas [20,21]: are delimited as follows: R 1 by the internal diameters of the recirculation passage and of the solenoid, and R 2 by the external diameters of the solenoid and of the armature [20]. As far as the hydraulic submodel of the pressure-balanced pilot valve is concerned, the flow-rate through the pilot valve, due to dynamic leakages, can be modeled as follows:…”

Development and assessment of a new operating principle for the measurement of unsteady flow rates in high-pressure pipelines

“…An advanced one-dimensional numerical model of the complete CR system from pump delivery onward was developed and assessed in [4]. The schematic of the injection-system hydraulic circuit was basically made up of chamber and pipe elements.…”

“…At present, in technical applications liquid flow rates at pressure levels higher than 300 bar can be accurately predicted only by means of refined numerical models. However, such an approach often involves advanced modelling of the mechanical, electronic and hydraulic components [4] that constitute the system, and therefore it is generally onerous and inefficient.…”

“…Since no commercial measuring device exists, allowing reliable evaluation of high-pressure flow rates above 300 bar, the validation of the proposed flowmeter was carried out by comparison with numerical results. These were achieved at the injector-supplying pipe of a CR system by a previously developed refined mathematical model of the complete injection apparatus [4].…”

On the Effect of a Rail Pressure Error State Observer in Reducing Fuel Injection Cycle-to-Cycle Variation in an Opposed-Piston Compression Ignition Engine

“…With the motive of quantitatively fixing the sensor-measured rail pressure, Catania et al [17,18] proposed a lumped parameter model to evaluate the rail pressure value which is significantly different from the sensor-measured rail pressure. Subsequently, Lino et al [19] established a nonlinear equilibrium model of fuel mass flow rate in CRS and found the unbalanced flow to be an important factor in pressure oscillation generation and applied the sliding mode control method in pressure oscillation suppression.…”