Heat transfer and knock modeling in a downsized spark-ignition turbocharged engine

In the present paper a combined procedure for the quasi-dimensional modeling of both heat transfer, combustion and knock phenomena in a "Downsized" Spark-Ignition Turbocharged Engine is presented. The procedure is extended to include the cycle-by-cycle variations effects, too. Heat transfer is modeled by means of a commercial software procedure (GT-Power) employing a finite element (FE) model of the combustion chamber. Combustion model is based on a fractal description of the flame front area. Cyclic dispersion is characterized through the introduction of a random variation on a number of parameters controlling the rate of heat release (air/fuel ratio, initial flame kernel duration and radius, EGR rate, turbulence intensity). The intensity of the random variation is specified in order to realize an Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV) similar to the experimentally observed one. A kinetic scheme is then solved within the unburned gas zone, characterized by different thermodynamic conditions occurring cycle-bycycle. In this way, an optimal choice of the "knock-limited" spark advance can be carried out and compared with the experimental data.