Deflagration dynamics of ammonia-syngas-air premixed flames in T-type tube

Abstract

In the context of carbon peak carbon neutrality, the carbon-free emission of NH3 combustion has received increasing attention within the field of combustion, but due to the low activity of NH3, research has generally been carried out through NH3 blending with other more active hydrocarbon fuels. In this work, a combination of experimental and simulation approach was used to study the premixed flame combustion characteristics of ammonia-syngas-air mixture. Two fuels, NH3 and H2 (one of the main components of syngas), were used as the main body of the mixture and their volume fractions were set to vary from 0 to 1, respectively. Then comparative analyses were performed on the flame base combustion characteristics. The results of the study showed that an increase in the volume fraction of NH3 decreases the flame propagation speed, while H2 has the opposite effect. For example, when both NH3 and H2 volume fractions were 0.6, the time required for the premixed flame to travel from the combustion chamber bifurcation to rush out of the pipe was 15 ms and 3.5 ms, respectively. The stability of the flame also decreased with the increase of NH3 content, the fold area of the flame tip increased, and the flame tip structure became cellular at 81 ms when the NH3 volume fraction was 0.6. With the increase of NH3 volume fraction, Lewis gradually decreases, and the decrease rate of Lewis is basically the same, linearly decreasing. The Lewis of pure ammonia combustion is less than the critical value of 1, and the flame is unconditionally unstable. The stability of the flame of the gas mixture with H2 as the main fuel is with the increase of the volume fraction of H2 first rise and then fall, the most stable is X(H2) = 0.7, Lev = 1.16495, when the volume fraction of CO and NH3 in the fuel are both 0.15. Meanwhile, the main reaction paths in the combustion reaction process are similar for both fuel bodies, but the rate of each reaction path in the NOx formation process is faster when H2 is the fuel body.