Analysis of the NH3 blended ratio on the impinging flame structure in non-premixed CH4/NH3/air combustion

Abstract

Ammonia as a carbon-free and high-hydrogen fuel with high energy density, is considered a promising alternative fuel. The impinging combustion characteristics of ammonia/hydrocarbon fuel blends are investigated, which can overcome the weaknesses of pure ammonia fuel such as low flammability and unstable combustion. The coupling effect of ammonia blended ratios ranging from 5% to 30% and flame-wall interaction is focused on the non-premixed impinging flame using Particle Image Velocimetry experiments and Large Eddy Simulation. Results show that the flame colors of low NH3 blended ratio are divided into two parts, brighter yellow at the top and blue at the bottom. However, the blue flame disappears and the yellow one gradually takes over the entire flame with the increase of NH3 blended ratios. It is also noted that the attached-wall flame extension distance is shortened with the increase of NH3 blended ratio, which is related with the phenomenon of wall quenching due to the coupling action of the flame-wall interaction and NH3 blended ratios. The phenomenon is attributed to the diffusive and convective instabilities indicated by the vorticity distribution. Besides, the CO2 and CO distributions show that the increase of NH3 blended ratios can effectively reduce the emissions of carbon oxide. Meanwhile, the wide range of high temperature area is formed in 20% NH3 blended ratio case, which promotes the progress of chemical reaction. And then the amount of NO and other key species rises sharply in 20% NH3 blended ratio case in the near wall region, which can consequently affect the flame compositional structure.