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The application of supercharging as a measure to improve the engine performances is a basic feature for downsizing concepts applied for advanced automobile engines. The adaptation of such concept to a high speed compact SI engine with a speed range between 2.000rpm and 9.000rpm forms the object of this paper. The determination of the special adapted control strategy as well as the necessary modifications of the basic engine were conducted in this work by mean of simulation with the 1D Code BOOST and coupled modules from 3D simulation by the code FIRE. The used models were generated and calibrated going out from the individual components to be connected: an 1000cc/2 cylinder/4 stroke engine and a screw type compressor. The adaptation of the engine to the supercharging concept, imposed modifications of the valve course and timing as well as of the intake ducts shaping.

The internal mixture formation within SI engines using fuel direct injection has a significant potential regarding the reduction of bsfc and pollutant emission. However the short time available for injection and spray distribution, as well as the complexity of the fluid dynamic conditions, amplified in a wide load and speed range, form a different base for the combustion process than using external mixture formation. The intend of the present study is to develop a method for modeling and optimization of mixture formation and combustion using a general approach for the fuel direct injection, which consist in the modulation of the injection rate, independently on the engine speed. In the first stage of modeling, the optimum combination between mixture formation elements as fuel pressure history, injection timing, spray characteristics, injector location or combustion chamber design is of great importance, forming the conditions for the subsequent combustion process.

High power-to-volume ratio and significant reduction of fuel consumption and pollution are paramount development targets for both SI and CI engines for automotive propulsion. Their implementation within a broad function range generated modular technical solutions - as elements of a general down-sizing platform - which are successful applicable in both SI and CI engines. The effects of such techniques, from super-charging or turbocharging, variable valve control and direct injection up to exhaust gas recirculation, autoignition-generated combustion and catalyst system indicate a merging which causes a basic discussion about the convergence of SI and CI engines.

The potential of fuel direct injection regarding the performances of a SI engine is transformable in significant advantages only by an accurate control of the internal air/fuel mixture formation. A main control element is the adaptability of the injection law, respectively of the spray characteristics to the thermodynamic conditions within the combustion chamber for different load and speed. This paper presents a method for the effective implementation of GDI techniques to SI engines, which is exemplified by a system with injection law modulation by pressure. The method is based of the interactive optimization of the processes within the combustion chamber respectively within the injection system, by a feed-back strategy between separate numerical simulations of both systems. For both modules the calibration is ensured by appropriate experimental analysis.

The paper presents the results of a down-sizing concept implicating gasoline direct injection, which is applied to a four-stroke four-valve SI engine with a displacement of 500 ccm per cylinder. The typical features of a down sized engine such as a high level of engine speed, high power density at low fuel consumption and a low level of pollutant emission form the main targets of this study. Numerical models of the process stages have been developed in 1D and 3D CFD codes. The accurateness of the models has been proved using experimental results. The main work consisted on the application of a direct injection system to the engine. The compact engine design and the high compression ratio have been maintained resulting in a combustion chamber design without any cavities or bowls. To obtain accurate results, the simulation work has been carried out using two different CFD-codes (FIRE and VECTIS); the results have been analyzed and compared.

The balance of the exchange between internal combustion engines and the environment regarding both consumption and emissions depends principally on the type of working substance, respectively on their management during the process within the engine. Regarding the process management, the internal mixture formation by direct injection has a better potential for reduction of both consumption and pollutant emission than external mixture formation, by carburetor or manifold injection. This fact results from the possibilities of control extended up to the start of combustion and is well demonstrated by recent developments. On the other hand, the limited availability of fossil resources, as well as the stringent requirement of a partial CO2 re-circulation in the atmosphere imposes an increased use of alternative fuels. The paper presents the performances obtained with a direct injection system with high pressure modulation when using different gasoline/methanol ratios.

The injection rate modulation and the spray characteristics are determining factors for the quality of mixture formation when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of a type of injection system to an engine with known requirements. The increased interest for the utilization of regenerative fuels - such as methanol obtained from biomass - as well as the success of previous utilization scenarios of variable gasoline/methanol mixture using manifold injection formed the base of the present analysis: the paper describes the results concerning injection performances and spray characteristics when using gasoline/methanol mixtures with different ratios in a direct injection system with high pressure modulation. The results are compared for different parameters of the injection systems as follows: injection volume, injector opening pressure, needle lift, pintle/seat geometry.

The fuel direct injection in SI engines is demonstrating a remarkable potential regarding the reduction of consumption and pollutant emission. Nevertheless, the management of the mixture formation “in-cylinder” - in conditions of a short duration and of a complex fluid dynamic configuration imposes both an accurate modeling and an exact control of the process. The problem gains on complexity when considering the use of alternative fuels which becomes more and more a subject of actuality. The paper presents a comparative analysis of mixture formation process and engine performances, when applying direct injection of gasoline, respectively of ethanol in a four-stroke single cylinder SI engine. The modulation of the injection rate shape is the result of a fuel high pressure wave, generated in a pressure pulse direct injection system.

The development of advanced techniques for an improved control of scavenging, mixture formation and thereby of the combustion in IC engines is more and more supported by numerical simulation models. However, the benefits in reducing the specific fuel consumption and the pollutant emission are not spectacular. On the other hand, the recent evolution of the fuel cell systems - which let expect a commercial application for automotive propulsion in the next years - demonstrates a remarkable efficiency. There appears a challenge for the IC engines, considering the utilization of similar energetic sources for both systems. This imposes an accelerated optimization of the processes in thermal engines - the central problem being the control of combustion. In this context, the basic models should be reconsidered.

The internal mixture formation by gasoline direct injection offers a remarkable potential to improve the engine performances and to reduce the pollutant emission, due to the large possibilities of process control. On the other hand, the control mechanisms their selves are more complex and sensitive at speed or load variations than the ones used for external mixture formation. The spray characteristics, as well as the shape of injection rate have to be accurately adapted to every condition of load, speed and surrounding. This paper presents a method for the effective optimization of GDI techniques for SI engines, which is exemplified by a system with direct injection by high pressure modulation. The method is based on the interactive optimization of the processes within the injection system respectively during the spray evolution, by a feed-back strategy between separate numerical simulations of both processes.