Numerical Investigation on Turbulent Non-premixed Methanol Flames Using Conditional Source-term Estimation

Abstract

Conditional Source-term Estimation (CSE) is a turbulent combustion model that uses conditional averages to close the chemical source term. Previous CSE studies have shown that the model is able to predict the flame characteristics successfully, however, these studies have only focused on simple hydrocarbon fuels mostly composed of methane. The objective of the present study is to evaluate the capabilities of CSE applied to turbulent non-premixed methanol flames, which has never been done previously. The present study investigates two different types of methanol flames: piloted and bluff -body flames. For the piloted flame, the standard k-􀀀ϵ model is used for turbulence modelling, while the Shear Stress Transport (SST) k-ω model is used in the bluff-body case. Different values of empirical constants within the turbulence models are tested, and C_ϵ1 = 1:7 for the piloted flame and γ_2 = 0:66 for the bluff -body flame provide the most comparable predictions of mixing field to the experimental measurements. Detailed chemistry mechanism, GRI MECH 2.11, is included in tabulated form using the Trajectory Generated Low Dimensional Manifold (TGLDM) method. The predictions including both the Favre averaged and conditional mass fractions of the reactive species and temperature are compared with available experimental data and previous numerical results. Overall, the predictions by CSE for both the conditional and unconditional quantities are in a good agreement with the experimental data except for H_2. Sources of discrepancies are identified such as the chemical kinetics and neglect of differential diffusion. Large Eddy Simulations may help to improve the velocity and mixing field predictions.