The thermal and kinetic effects of O-3 on flame propagation were investigated experimentally and numerically by using C3H8/O-2/N-2 laminar lifted flames. Ozone produced by a dielectric barrier plasma discharge was isolated and measured quantitatively by using absorption spectroscopy. Significant kinetic enhancement by O-3 was observed by comparing flame stabilization locations with and without O-3 production. Experiments at atmospheric pressures showed an 8% enhancement in the flame propagation speed for 1260 ppm of O-3 addition to the O-3/N-2 oxidizer. Numerical simulations showed that the O-3 decomposition and reaction with H early in the pre-heat zone of the flame produced O and OH, respectively, from which the O reacted rapidly with C3H8 and produced additional OH. The subsequent reaction of OH with the fuel and fuel fragments, such as CH2O, provided chemical heat release at lower temperatures to enhance the flame propagation speed. It was shown that the kinetic effect on flame propagation enhancement by O-3 reaching the pre-heat zone of the flame for early oxidation of fuel was much greater than that by the thermal effect from the energy contained within O-3. For non-premixed laminar lifted flames, the kinetic enhancement by O-3 also induced changes to the hydrodynamics at the flame front which provided additional enhancement of the flame propagation speed. The present results will have a direct impact on the development of detailed plasma-flame kinetic mechanisms and provided a foundation for the study of combustion enhancement by O-2(a(1) Delta(g)) in part II of this investigation. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.