Premixed Turbulent Flames and Spectral Approach

Scientific and technical approach concerning the behaviour of flames developing in a turbulent medium are related in many recent papers. On the whole the problem is very complex!The chemical reaction develops inside a turbulent flow which requires a double scaling. Characteristic times and characteristic lengths have to be defined for both flame and the turbulent fields. With a view to enlarging these comparisons a spectral analyses of the turbulent field is proposed. It is widely supported by previous experimental data. The flame can be acted upon by an external turbulent fields. That supposes the flame to be thicker that the smallest turbulent structures in connection with the Kolmogorov scale. With increasing Reynolds numbers turbulent structures penetrate the flame front, they can disturb the preheat zone or event the chemical zone. The passage of a flame front regime to the case of a chemical reaction developing in a volume is thereby emphasized. As the reaction rate is decreasing, the domain affected by the reaction is increased chemical reactions generate a segregation process whereas the chemical species are mixed by the turbulent motion. In the premixed combustion engine a large range of operating points can be defined. The diagram usually used is that of Barrere Borghi. Several modeling methods should probably be developed according to the positions of the operating points in the diagram. Modeling methods are not presented herein. However the existence of typical structures in connection with the architecture of the combustion chamber could be examined in subsequent paper. The flame front can be subjected to distorting effects due to isolated rolling or to a sequence of vortices. Previously this last case has been touched upon. Using a spectral approach no discremination has to be made as for the sizes of these rollings: that could lead to new modeling methods if restricted shapes of vortices are accepted. By using a spectral method the behaviour of flames developing in a turbulent field can be easily understood. This approach could also open the way to new modeling methods.