A control oriented model of a Common-Rail System for Gasoline Direct Injection Engine Alessandro di Gaeta, Giovanni Fiengo, Angelo Palladino and Veniero Giglio Abstract— Electronics has greatly contributed to the develop- ment of internal combustion engine. This progress has resulted in reducing environmental degradation, and yet continuing to support improvements in performance. Regarding gasoline engine, a considerable step forward has been achieved by Common Rail (CR) technology able to exactly regulate the injection pressure during whole engine speed range. As a consequence, the injection of a fixed amount of fuel is more precise and it is possible to perform multiple injections for combustion cycle. In this paper, the authors present a mean value model aimed at the control of a CR system for a Gasoline Direct Injection (GDI) engine. The model is based on the descriptions of electro- valve, including the actuator circuit, and the fuel pressure in the rail. The performances of the proposed model are finally depicted through comparisons with experimental data collected by a CR system mounted on a 2.0 liters spark ignition engine, showing a good accuracy and reliability. I. INTRODUCTION Today, an huge effort is devoted by companies to preserve the earth’s environment. In particular, automobile industry has to comply both the reduction of pollutant emissions enforced by international regulations and the improvement of performance required by the customers. In this scenario, the GDI engines with High Pressure (HP) fuel injection systems, based on the CR architecture, can be considered a good solution to this aim. In fact, electronically controlled HP fuel injection system holds an important role concerning both the emission control strategy and the improvement of internal combustion engine performance [1], [2]. High pressure injection allows to finely atomize the fuel spray and to promote fuel and air mixing, resulting in significant combustion improvements [3], [4]. Following the previous consideration about the pollutant emissions and consequent role of HP system to reduce it, the prediction of CR equipment behavior is of practical relevance in design of automotive engine. In literature, extensive research is conducted for diesel engines to reduce both NO x and particulate (soot) emissions [5], [6], [7], or to improve the mass transfer characteristics to the catalytic surface through the analysis of a diesel oxidation catalyst [8]. In spark ignition engine, the CR system can be This work was supported by the Italian Ministry for University and Research in the framework of the FIRB projects. A. di Gaeta and V. Giglio are with Istituto Motori, National Research Council, 80125 Napoli, Italy. E-mail: {a.digaeta, v.giglio}@im.cnr.it. G. Fiengo and A. Palladino are with the Dipartimento di Ingegneria, University of Sannio, 82100 Benevento, Italy. E-mail: {gifiengo, angelo.palladino}@unisannio.it. useful to reduce the exhaust emission and fuel consumption and to improve the driving dynamics [9]. For example, for diesel engines, the use of CR injection systems improves performance and customers perception. In this case the modern CR systems allow multiple injections with a limited dwell time between injections, but the use of multiple injections generates a series of pressure waves, due to the closure of the injectors, which make constant injection pressure a pure theoretical assumption. In this perspective, the CR system represents a quenched oscillating system, in which the pressure waves generated by the first injection pulse produce a variation in the in- jection pressure of the subsequent injections [10]. Many CR injection models have been previously proposed, based on the equations of the physics underlying the process or alternatively developed through simulation packages. The form of these models is suitable for mechanical design but is often too complex to be appropriate for control purposes. In [11] and [12] innovative approaches in automotive control application have been considered, respectively based on mean value engine models and the discrete-continuous interactions in the fuel injection system, due to the slow time- varying frequency of the HP pump cycles and the fast sam- pling frequency of sensing and actuation. Whereas, a rather complete mathematical model for a common-rail injection- system dynamics numerical simulation was developed in [13] to support experimentation, layout, and control design, as well as performance optimization. In [14] and [15] an accurate model considers the fuel injection system of diesel engines with a distributor-type pump and properly represents the unsteady flow in the pipeline connecting the jerk pump and the injector. Then the resulting hyperbolic equations are solved by using an explicit scheme of the predictor corrector type. The authors in [16] consider the same complex fluid- dynamic phenomena and study the instability in a CR injec- tion system for high speed diesel engines. The good accuracy of all these models is counterpoised by the complexity of the resulting equations. In this context, the paper presents a regulation oriented model of a common-rail system for GDI engines. The proposed model is obtained exploiting the descriptions of electro-valve dynamics and of steady fuel pressure in rail. Moreover, in this work, the analysis of CR system is completed by the study of pressure alternating component, present in the HP circuit and generated by the pump in absence of injections. The robustness of the model is tested comparing some measurable variables with experimental Joint 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference Shanghai, P.R. China, December 16-18, 2009 FrA09.6 978-1-4244-3872-3/09/$25.00 ©2009 IEEE 6614