Effects of coflow velocity and coflow moisture contents on the formation and emissions of CO/NO in non-premixed impinging flames

Abstract

The emission characteristics of non-premixed impinging flames are investigated using PIV experiments and numerical simulations. Different coflow conditions are conducted to focus on the pollutant emissions with the flame-wall interaction. Results show that flame dynamics obtained from experiments are in good agreement with that calculated from numerical simulations, and flame instability is intensified in near wall region in large coflow velocity case. In addition, the increase of coflow velocity may promote CO production, especially in low mean mixture fraction region (0.07-0.26). The distribution of CO is dispersed in large coflow velocity case, which is related with a strong convection and diffusion process. Besides, it is found that the decrease of flame temperature and the large wall quenching distance is observed with the increase of coflow moisture content, which is associated with the weakened combustion progress and the migration of reaction zone due to the decrease of O2 concentration in coflow mixture and the increase of specific heat capacity. The decrease distribution of local emission indexes of CO and NO is also shown in high coflow moisture content case, which can weaken the production of CO, thermal NO and prompt NO, and accelerate the consumption of NO. Moreover, CO reduction occurs mainly in high CO concentration region, while NO reduction is observed in the whole flow field. Results indicate that small coflow velocity and high coflow moisture content are beneficial to supress pollutant emissions, which can provide reference data for the optimization of clean combustion devices.