Unsteady flame–wall interaction: Impact on CO emission and wall heat flux

Abstract

This study investigates the interaction of a two-dimensional (2D) laminar methane-air premixed flame with a constant temperature wall using Direct Numerical Simulation (DNS). The flame is excited using velocity perturbations at the inlet for a range of forcing frequencies. The GRI 3.0 chemical mechanism is used to perform the simulations. The flame behaviour is first analysed by comparing the results to those observed for a steady 2D laminar flame interacting with the wall and a one-dimensional head-on quenching (HOQ) flame under the same conditions as the 2D flame. This is followed by analysing the wall heat flux and CO emission due to the flame quenching at the wall for different forcing frequencies. At low forcing frequencies, the flame is observed to sweep against a large portion of the wall whereas at high frequencies, the flame has an insignificant response to the incoming velocity perturbations. In both these regimes, side-wall quenching (SWQ) is the dominant mechanism of flame–wall interaction. However, at an intermediate frequency, both HOQ and SWQ occur at different stages of flame–wall interaction. The analysis of the total integrated wall heat flux of forced flames shows a large variation of this quantity compared with a steady state flame, with the highest fluctuations occurring for the flame forced at the intermediate frequency. The radical recombination reactions are found to be significant in the vicinity of the wall, contributing to about 50% of the total HRR at the wall at the quenching instant. The analysis of the species transport budget for CO shows that CO transport near the wall close to the flame tip is dominated by convection and diffusion.