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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. Following optimization parameters have been taken into account: injector and spark plug location, injection timing and duration as well as intake duct design. The optimization results in terms of mixture formation by direct injection and the combustion, are presented in the paper. Complete Paper available under: http://www.sae.org/servlets/productDetail?PRO D_TYP=PAPER&PROD_CD=2003-01-0541

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. Moreover the interaction between fuel and air flow within the cylinder during the mixture formation is determining for the flame propagation. The model was developed in base of the commercial code FLUENT. Different combinations of fuel quantity, injection timing, fuel/air interaction and engine speed are represented as timeand spacerelated sequences of mixture formation. The program calibration is made by spray visualization for distinct cases, as a base of reliable simulation in a wide range of parameters. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_T YP=PAPER&PROD_CD=2000-01-0648