Experimental and chemical kinetic study on effects of H2-DME fusion addition on laminar premixed flame speed and flame instability for ammonia composite combustion

Improvement of the laminar flame speed and stability for ammonia combustion by using H₂ and DME has received significant attention. In this study, the characteristics of NH₃/H₂, NH₃/DME and NH₃/H₂/DME were investigated in constant-volume bomb with high-speed schlieren technique and chemical kinetics. The results show that DME or H₂ addition mainly acts as “start-up" or “acceleration" for ammonia laminar flame speed increasing, respectively. In NH₃/H₂/DME laminar flame, the increase of DME addition ratio not only increases the intensity but also advances the onset of self-acceleration. At ammonia substitution ratio of 10 %–70 %, the Markstein length of NH₃/H₂/DME flame are all significantly improved compared with pure ammonia flame. The H₂-DME fusion-addition can mitigate the reduction of flame thickness and keep a relatively minor thermal expansion ratio. In NH₃/H₂/DME laminar flame, DME addition can increase the Lewis number greater than 1.0 at ammonia substitution ratio of 10 %–40 %, which significantly reduce the thermo-mass diffusion instability in comparison with H₂ addition. Based on mixture design method and experimental validation, it was found that the flame speed at 473 K, 5 bar and φ = 1 for NH₃/H₂/DME blending ratios of 53.94 %/26.61 %/19.45 % are greater than those of NH₃/H₂ and NH₃/DME with the same ammonia substitution ratios.