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Spark-ignition engines are characterized by poor levels of thermal efficiency, it is known, especially when running at partial load. Since part-load operating points are the most commonly used in engine average life, achieving a given torque value with small displacement, high mean effective pressure engines, the so-called “downsizing”, permits, in general, to limit some typical engine losses (for instance: pumping and friction losses), improving the fuel consumption in a wide range of engine operating points. Small displacement engines, usually, achieve high toque values thanks to supercharging techniques. In this paper, knock risks for a small displacement turbo-charged spark-ignition engine have been analyzed. A parametric analysis of numerous variable influencing engine performance and knock resistance has been carried out by means of 1-D numerical simulations.

The intake system of a wide commercial spread spark-ignition engine has been modeled by using a 3-D code. The present configuration of the inlet manifold and inlet port does not generate any organized charge rotation, especially at low rotational speed. Objective of this paper is the research of new solutions, able to produce higher turbulence levels of the in-cylinder flow, without lowering the engine volumetric efficiency, in order to shorten the combustion duration and improve the energy conversion quality. A three-dimensional model for the calculation of the inlet port and valve performance under steady conditions has been developed. First, the normal production intake system has been modeled to the aim of validating the model set-up. The inlet valve discharge coefficient in a steady flow has been calculated. The results obtained showed a good agreement to the measured data and encouraged the authors to use the model for the development of new intake solutions.