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Recently, a tendency is consolidating to produce low displacement turbocharged spark-ignition engines. This design philosophy, known as "engine downsizing", allows to reduce mechanical and pumping losses at low load as a consequence of the higher operating Brake Mean Effective Pressure (BMEP). The presence of the turbocharger allows to restore the maximum power output of the larger displacement engine. Additional advantages are a higher low-speed torque and hence a better drivability and fun-to-drive. Of course, at high loads, the spark-advance must be carefully controlled to avoid the knock occurrence and this determines a substantial penalization of the fuel consumption. The knowledge of the knock-limited spark timing is hence a key point in order to reduce the fuel consumption drop at high loads.

CFD techniques are more and more utilized in the development of new solutions for performance improvement of internal combustion engines.\ud \ud Three dimensional models, in general, are able to provide detailed and sound information on engine phenomena, but often they are time consuming and hard to be implemented. On the other hand, one-dimensional models can reproduce the entire engine cycle with acceptable computational times; however they need semi-empirical correlations in order to model the flow field details and the burning speed within each cylinder.\ud \ud In this paper, an example of hierarchical structure of 3-D and 1-D models has been proposed. The main performances of a small turbocharged spark-ignition engine have been calculated. Variable-speed and full load operating points have been analyzed. The 3-D model provided the details of the in-cylinder flow field and turbulent indices. These results have been utilized as reference data in tuning a quasi-dimensional turbulent combustion model, included within a 1-D model of a “downsized” turbocharged spark-ignition (SI) engine. Combustion modeling utilizes a deeply validated approach based on a fractal schematization of the flame front surface. Knock occurrence has been predicted by the solution of a kinetic-scheme inside the “end-gas” unburned zone. Once tuned, the one-dimensional code has been finally applied to find the knock-limited spark-advance at wide-open-throttle conditions, for different engine speeds. Numerical results have been compared to the experimentally determined values and a good agreement has been found.\ud \ud This work demonstrates as matching models of different hierarchical levels could be a useful tool in the industrial development of high efficiency engines

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The paper reports the research activity related to the development of a twin-spark Sl engine equipped with a variable valve timing (VVT) device. Improvements on the fuel consumption at part load are expected when an high internal exhaust gas recirculation (internal EGR) level is realized with a proper phasing of the VVT device. The twin-spark solution is implemented to improve the burning speed at low load, and to increase the EGR tolerance levels. Both experimental and theoretical analyses are carried out to investigate the real advantages of the proposed engine architecture. In particular an original quasi-dimensional model for the simulation of the burning process in a twin-spark engine is presented. The model is mainly utilized to find the proper combination of VVT device position (and hence EGR level) and spark advance for different engine operating conditions. A comparison with the single-spark solution is also provided. In addition, a procedure for the estimation of the sound pressure levels originated from the combustion process is utilized, to estimate the increased radiated noise associated to the double ignition. The model is well suited to define the control strategy maps of the engine in its whole operating range