The paper is focused on the development of a fractal combustion model, included within a whole-engine one-dimensional model (1Dime code). An extensive validation is carried out through the comparison with experimental data. The experimental activity was carried out in the combustion chamber of an optically accessible one-cylinder engine, equipped with a commercial head. Experimental data basically consisted on optical measurements which were also correlated to the instantaneous pressure inside the cylinder. Optical measurements were based on 2D digital imaging and UV chemiluminescence of radical species. The rate of chemical energy release and related parameters were evaluated from the in-cylinder pressure data using interpretation models for heat release analysis. Moreover a post-processing of the optical measurements allowed to define the mean flame radius, and propagation speeds as well, as a function of the crank angle. Theoretical and experimental analyses allowed to fully characterize flame structure and propagation speed as well. In order to estimate prediction levels and limitations of the numerical procedure, different engine speeds and spark timings were experimentally analyzed. A good agreement has been found in the whole tested range.