Turbulent flame propagation process in a spark-ignition (SI) engine is theoretically investigated. Fueling with gasoline, ethanol and different gasoline-ethanol blends is considered. A quasi-dimensional SI engine cycle model previously developed by the author is used to predict the thermodynamic state of the cylinder charge during the cycle. The flame is assumed to be spherical in shape and centered at the spark plug. Computations are carried out for an automobile SI engine having a disc-shaped combustion chamber, for which the compression ratio and the nominal speed are 9.2 and 5800 rpm, respectively. Geometrical features (flame radius, flame front area and enflamed volume) of the flame, combustion characteristics (mass fraction burned and burn duration), and cylinder pressure and temperature are predicted as a function of the crank angle. Three different positions of the crank angle are studied: -10 degrees, TC and +10 degrees. It was concluded that ethanol addition to gasoline up to 25 vol % accelerated the flame propagation process. (c) 2006 Elsevier Ltd. All rights reserved.