Eddy break-up model and fractal theory: comparisons with experiments

Abstract

This paper deals with predictive methods of the combustion rates in the case of premixed mixtures. Comparisons are made between two of these predictive methods. The first approach is based on a standard eddy break-up (EBU) model supplemented by a condition on the chemical composition of the mixture. The reaction can develop within a fixed range of richness. The second method uses the concept of fractal surfaces. Moreover a spectral analysis allows us to introduce the role of the small turbulent structures embedded in the preheat zone. By means of the concept of fractal surfaces the real area of the flame surface can be predicted starting from its mean value and from L (integral length scale), u′ and ϑ k (Kolmogorov length scale). The location of the flame is deduced from the standard EBU model previously referred to. u′ ànd {ε} are also known along the mean flame surface. The area of the real indented surface can be inferred. The combustion rate can be deduced by associating the area of the flame front with a convenient flame speed accounting for the role of the small structures embedded in the preheat zone. The results found by the two methods do not depart from each other by more than 10%