Combustion Characteristics of Ammonia/Air Premixtures at Different Temperatures

To further investigate the combustion characteristics and influencing factors of ammonia （NH₃）， under different temperatures， a constant-volume combustion bomb and a high-speed schlieren imaging system were used to examine the laminar burning velocity and flame instability of NH₃ at different initial temperatures and equivalence ratios. Additionally， chemical kinetic studies on ammonia premixed combustion were conducted via CHEMKIN. The results indicate that as the initial temperature increases， the laminar burning velocity increases， and the Markstein length decreases slightly. The sensitivity of the reactions is less affected by temperatures. When the equivalence ratio was 1.1 and the temperature rised from 373 K to 473 K， the laminar burning velocity increased by 68.6%. With the increase of the equivalence ratio， the laminar burning velocity first increased and then decreased， reaching the peak value at the equivalence ratio 1.1. The Markstein length increases with the increasing equivalence ratio. Within the experimental conditions， the flame front exhibits almost no cellular structure. Buoyancy instability follows a trend of “first weakening and then strengthening” with changes in the equivalence ratio， which is exactly opposite to the variation trend of laminar burning velocity. Reaction R39（H+O₂O+OH） promotes combustion by regulating O and OH， and its variation trend is consistent with that of the flame velocity.