Turbulent flames investigation of methane and syngas fuels with the perspective of near-wall treatment models

Abstract

The near-wall treatment models play an important role in accurate turbulent flow simulation, particularly the ones close to the boundary layer. In the study, three k−ε epsilon near-wall treatment models, such as Enhanced Wall Treatment, Standard Wall Functions, and Scalable Wall Functions, have been numerically studied to verify the experimental results of methane combustion performed by Brookes and Moss within a laboratory-scale rig. Then, the turbulent flame of methane investigated at various wall distance (y∗) ranges specifically 0 < y∗ < 1, 1 < y∗ < 11.225, 11.225 < y∗ < 30, and 30 < y∗ < 500 to determine the effects of the mesh structures and y∗ on the numerical results. Following the validation of the near-wall treatment models and y∗, the turbulent combustion flame of methane and three syngas fuels were numerically investigated at the same thermal power, 8.6 kW. H2/CO ratios of the syngas 1, syngas 2, and syngas 3 are 2.36, 1.26, and 0.63, respectively. The maximum flame temperatures inside the chamber depend on the type of fuel, fuel species, and the percentage of the species. The results of the work show that Enhanced Wall Treatment presents better prediction as compared to the others, not only at 0 < y∗ < 1 but also at the other wall distance ranges. Standard Wall Functions demonstrates approximately the same results as compared to Scalable Wall Functions. Besides, the NO emissions in the flue gas of the syngas fuels are higher than methane due to higher flame temperatures and unburned hydrocarbon species. Furthermore, increment the H2/CO ratio for syngas fuels causes an increase in flame length, diameter, and temperature as well as NO emissions.