Effect of H2 addition on laminar burning velocity of NH3/DME blends by experimental and numerical method using a reduced mechanism

Author：Li, H. Z., Xiao, H. H.

Journal：Combustion and Flame

DOI:  10.1016/j.combustflame.2023.113000

Keywords: H-3/DME blends, Hydrogen, Markstein length, Laminar burning velocity, Reduced mechanism, hydrogen-air flames, ignition delay, markstein numbers, premixed flames, dimethyl ether

Abstract: 

Blending dimethyl ether (DME) into ammonia (NH3) can efficiently enhance the combustion of pure NH3, and has attracted increasing attention. Partial dissociation of NH3 can convert NH3/DME to NH3/DME/H-2 mixtures. This work measured the Markstein length and laminar burning velocity of NH3/DME/air mixtures for different blend ratios (100/0, 80/20, 40/60, and 0/100) with various H-2 additions (0%, 20%, and 40%) at phi = 0.7-1.7, 0.1 MPa, and 298 K using a spherical constant-volume combustion method. A reduced kinetics mechanism was developed and optimized based on own prior detailed mechanism. This model gives more accurate predictions for NH3, DME, NH3/DME, and NH3/DME/H-2 compared to previous models in terms of laminar burning velocity, ignition delay time, and species concentration. The experimental and modeling results show that the measured Markstein length of NH3/DME/H-2 blends as a function of equivalence ratio presents different states for different NH3/DME blend ratios. The existence of H-2 can effectively increase the laminar burning velocity of NH3/DME/air mixtures. Relative increase in laminar burning velocity (E-SL) shows a non-monotonic tendency with increasing equivalence ratio for different H-2 additions. The peak value of E-SL for NH3/DME/air mixtures with various H-2 additions appears at around phi = 1.5. This can be attributed to the dominant effect of C-contain and N-contain reactions rather than H-O reactions at the rich burn side. Similar to E-SL, the free radicals that dominate laminar burning velocity may transit from H, O, and OH to C-H and N-H radicals at around phi = 1.3 similar to 1.6. The thermal effect also contributes to the E-SL and laminar burning velocity for rich fuel. (c) 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.