(364g) A Multi-Phase Multi-Component Flamelet Generated Manifold for Spray Combustion Simulations

Accurate and affordable predictive numerical simulations of spray combustion processes continue to be an important aspect to address the operability of liquid-fueled energy systems such as gas turbines. The flamelet model is a promising approach to account for detailed chemistry in turbulent combustion modeling. However, the traditional diffusion flamelet is unable to capture the evaporative heat loss when applied to spray combustion, leading to significant over-prediction of temperature. In this study, a model flame of the quasi-1D counterflow spray flame has been developed. The two-dimensional multiphase convection-diffusion-reaction (CDR) equations have been simplified to one dimension using similarity reduction under the Eulerian-Eulerian two-fluid model framework. This model flame is capable of directly accounting for non-adiabatic heat loss as well as multiple combustion regimes present in realistic spray combustion processes. A recently developed surrogate fuel that can mimic both thermo-physical (including distillation curve) and chemical kinetics (ignition and combustion) characteristics of real kerosene fuels was used for fuel modeling. This surrogate fuel covers major hydrocarbon groups of typical kerosene fuels of linear paraffin, cyclo-paraffins, and aromatics, and is composed of four components: n-dodecane/iso-cetane/trans-decalin/toluene with the mole fraction of 0.3/0.36/0.246/0.094. For chemical kinetics, a multi-component skeleton reaction mechanism of 231 species and 5591 reactions was used. The model flame has been analyzed to show that the counterflow spray flame is extinguished at a lower strain rate or scalar dissipation rate, compared to the single-phase counterflow diffusion flame. Due to liquid evaporation, there exists a non-monotonic behavior of the temperature/species mass fractions and a non-linear relation between the enthalpy and the mixture fraction, different from its gaseous counterpart. A spray flamelet library is then generated based on the model flame. To retrieve data from the spray flamelet library, the enthalpy is used as an additional controlling variable to represent the interphase heat transfer, while the chemical reaction process is mapped to the mixture fraction and the progress variable. The spray-flamelet/progress-variable (SFPV) approach is evaluated with the result from direct integration of finite-rate chemistry as a benchmark, carried out in a CFD simulation of multi-dimensional counterflow flame, representing the recirculation region in gas turbine combustors for flame stabilization. The performance of the SFPV approach will be addressed and discussed.