Description of the Mixing Status of Partially Premixed Flames Using Regime Diagram

Mansour, M., Description of the Mixing Status of Partially Premixed Flames Using Regime Diagram, , 2015/06/07.


Partially premixed combustion is one of the common modes for many practical combustion systems where the mixture is not homogenous and characterized by fluctuations in mixture fraction. This mode covers a wide range between fully premixed and non-premixed combustion modes. Quantitative description of the several regimes in partially premixed mode is essential for understanding and modeling the flame structure. In this work a new regime diagram describing the mixing status for partially premixed environment is proposed in order to be used for the characterization of partially premixed flames. The mixing regime diagram describes different regimes within the partially premixed mode. The limits of mixture fraction and its mean value within the mixture fraction field are used to classify those regimes. In addition, the range of flammability limits and its mean are used for normalization of the diagram axes. The diagram describes the nature of the regimes within the partially premixed conditions and thus provides quantitative tool for the analysis and discussion of partially premixed flames. It classifies the partially premixed modes into eight well defined regimes. In general, partially premixed mode is defined as non-homogenous mixture with pockets at different stoichiometric values. The limits of partially premixed regimes of different fuels are listed in this work. The link between the flame stability and its mixing status within the proposed diagram is discussed using mixture fraction measurements.Several partially premixed turbulent flames of methane and propane are selected in order to be located within the proposed diagram. The relation between the flame stability and its location within the diagram is then discussed. The data show that the location of the flames in the regime diagram is related to its stability characteristics. The proposed mixing regime diagram can thus be used as an initial step for the design of stable partially premixed flames based on its mixing characteristics.