Analysis of Near-Wall CO due to Unsteady Flame-Cooling Air Interaction

Abstract

The interaction of a stoichiometric, laminar premixed methane/air flame with a coolant jet is investigated using two-dimensional fully resolved simulations (FRSs). The flame is forced at the inlet with velocity modulation and the coolant is injected from a cooling hole located on the wall at the same temperature as the premixture. FRS cases featuring a combination of blowing ratios, forcing frequencies, position of the cooling hole and the coolant type (air and $$N_2$$ ) are studied to understand the effects of these parameters on flame dynamics and CO emissions. The results show a negligible impact of the forcing frequency on the exhaust CO emissions. However, increasing the blowing ratio and the cooling hole streamwise location both increase the exhaust CO emissions. Using air instead of nitrogen as the coolant reduces the CO emission by providing additional oxygen and therefore enhancing CO oxidation. Furthermore, analysis of the CO mass fraction in the near-wall, post-cooling hole region shows a strong dependence on the local temperature and the mixture fraction used as a measure of dilution. CO mass fraction—temperature ( $$Y_{CO} - T$$ ) scatter plots reveal the same trends as those of one-dimensional (1D) freely-propagating flames at different equivalence ratios up to a limit, identified using a progress variable based on the $$CO_2$$ mass fraction. The results of this work highlight the potential pathways for modelling the near-wall CO mass fraction in effusion cooled combustors.