Effect of H-2 addition on laminar burning velocity of NH3/DME blends by experimental and numerical method using a reduced mechanism

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.

Automated summary

This study measured the Markstein length and laminar burning velocity of NH3/DME/air mixtures for different blend ratios and varied H-2 additions. A reduced kinetics mechanism was developed based on a prior detailed mechanism, providing accurate predictions for NH3, DME, NH3/DME, and NH3/DME/H-2. The results showed that the existence of H-2 effectively increased the laminar burning velocity, and the peak value of laminar burning velocity occurred at a specific equivalence ratio. Rating: 8/10.