Experimental and simulated study of ammonia blending with DME steam reformed and cracked gases under lean-burn condition

Dimethyl ether (DME) steam reforming (SR) and cracking (CR) can not only achieve on-line production of hydrogen (H₂) and methane (CH₄) but also increase fuel energy. The ammonia blending with DME-SR or DME-CR gases is an effective method to enhance the reactivity of ammonia combustion. This paper aims to compare the effects of DME-SR and DME-CR on combustion and emissions under lean-burn condition. In the constant volume combustion chamber (CVCC) experiments, the in-chamber pressure and flame propagation process were measured for NH₃/H₂ and NH₃/CH₄ blends, and NO emissions were visualized by chemiluminescence. A three-dimensional (3D) model was established with validation by the experimental data. Based on this model, the effects of DME-SR and DME-CR on combustion process and NO_x emissions were studied. The results showed that both DME-SR and DME-CR can enhance the ammonia combustion process under lean-burn condition. The case with DME energy ratio 70% and the equivalence ratio of 0.4 for SR (X70ER0.4-SR), and X30ER0.5-SR can achieve faster combustion rates than pure ammonia at ER of 1.0 (X0ER0.9) due to the main reforming product of H₂. The ammonia blended with fuels from DME-SR and CR can help to improve the NO emission under lean-burn condition, being lower than X0ER0.9. These findings highlight the advantages of using DME-SR and DME-CR for improving the ammonia combustion. Considering the fuel energy increment, DME-CR could be potential to obtain better fuel economy and emission improvement in real engine application.