Liquid fuel spray atomisation, ignition and combustion dynamics

Abstract

Turbulent spray ames are increasingly found in industrial combustion devices due to greater demand for fuel exibility. However, a comprehensive model of the underlying physics involved into this is still lacking due to the great complexity of the problem. The importance of numerical studies in this context is related to the possible savings in experimental testing both in terms of time and resources. A detailed yet a ordable numerical tool is therefore required to the development of less polluting and more e cient devices. This work aims at the validation of existing models and developing methods focusing on the atomisation, evaporation, ignition, and combustion dynamics of spray fuelled burners. Here, extensive simulations are performed in the context of Large Eddy Simulation (LES) where the scalar elds are modelled using a transported pdf approach. The solution of the latter is obtained by means of the Eulerian stochastic eld method, a exible and comprehensive combustion model. The liquid phase is treated in a discrete Lagrangian fashion, where the sub-grid-scale

uctuations from the LES are accounted for by the stochastic parcel method for dispersion, break-up and evaporation. Di erent atomisation and evaporation models of increasing complexity are tested and greater insight on the e ect of this choice is provided. This is achieved while exploring the applicability of the method to various state of the art techniques for pollutants reduction. Several test cases have been simulated: the Sandia constant volume chamber, the DELFT hot co- ow burner and two of the burners from CORIA laboratories. For all cases good reproduction of the aerodynamic elds as well as the qualitative ame shapes is acheived. Three evaporation model have been tested, and three break-up models used for the simulations and the e ects of this choice are explored in this work. The stochastic break-up model tested allows for reduced a priori assumption on the calculation providing results comparable with other methods. The Abramzon-Sirignano evaporation model appears to be a valid evaporation model to be employed in dilute spray LES calculations. Validation is achieved by comparing both gas and liquid phase properties with the available experimental data. An important dependency of the quality of the predictions on the choice of the chemical mechanism describing the oxidation process is observed. As a conclusion of the study, future directions are suggested together with some preliminary illustrative results.