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In this paper, a parameter to quantify the cyclic variability in first stages of combustion is presented, as an evolution of the parameter proposed by Hill and Kapil. This parameter relates the mean time necessary for the initial flame to reach the periphery of a turbulence eddy structure moving from the flame kernel position. This parameter is used in combination with quasi-dimensional models in order to predict and analyze small-scale turbulence contribution to cyclic variations. The cyclic dispersion parameter could be introduced in the predictive models as a delay in the combustion beginning. The parameter is compared with the experimental standard deviations in mass burned fraction at spark time obtained from others researchers works and own experimental data. A satisfying agreement between predictions and measurements is achieved.

In this paper, models developed to determine exhaust emissions from Spark Ignition engines are shown. Concretely, a model based on chemical kinetics for determining CO and NOX emissions is presented. Also it is shown a model for the determination of the HC exhaust emissions based on retention in crevices, wall quenching, and in-cylinder and exhaust pipe post-flame combustion processes. Both models are included in a quasi-dimensional multizone model that permits the fast analysis and prediction of combustion in homogeneous-charge SI engines. Finally, results obtained from the models are compared with experimental exhaust emissions measured in a test bench.