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.