CONICET | Buscador de Institutos y Recursos Humanos

Partially premixed combustion is characterized by a variable equivalence ratio of the mixturein space and time, and where there are both lean and rich mixture zones. Thus the reaction evolves alongwith a turbulent mixture process, which modifies the composition of reactants and products. In thissituation a so-called triple flame could be encountered, in which a rich and a lean premixed flame frontas well as a diffusion flame are present. The diffusion flame develops behind the premixed flame frontdue to turbulent mixing in the hot combustion products. This kind of combustion could be found in DirectInjection Spark Ignition (DISI) engines when they are operated in the stratified charge mode. The modelconsidered in this work assumes a simplified one-step irreversible chemical reaction in which fuel andoxidant react together in stoichiometric proportions giving products with the composition correspondingto a complete combustion. A transport equation is solved for the oxidant and fuel, from which theamount of products and the combustion progress are computed, while the turbulence is modeled withRANS (Reynolds-Average Navier-Stokes). The reaction rate is assumed in the model as proportionalto the product of the Flame Surface Density (FSD) by the local laminar flame speed. Aside from thestate and composition of the mixture, the local laminar flame speed is afected by the turbulent mixingprocess. This mixing process is taken into account by means of the classical β-PDF (Probability DensityFunction), which is a function of the mixture fraction and its variance. A transport equation is solvedfor both, the mixture fraction and its variance, and the FSD is computed through a transport equationwhere several models are available for the source terms. The model is implemented in the open-sourcetoolkit OpenFOAM R . Computational results are obtained for partially premixed combustions insideconstant-volume vessels with several initial configurations, which are compared with numerical resultsavailable in the literature.