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Ammonia allows for long-distance and large-scale storage transport of renewable energy sources. The reactivity of NH 3 -Air flame can be enhanced by doping with hydrogen and by increasing the initial temperature. The flame combustion characteristics of NH 3 –H 2 -Air are studied in a rectangular closed pipe with a mole fraction of 45% H 2 , an equivalence ratio (φ) of 0.8–1.2 and 0.1 MPa. The initial temperatures (T u) of the mixture are 300 K, 375 K and 450 K. Experimental studies of flame front speed, flame tip structure evolution, and overpressure dynamics are performed. Laminar burning velocity (S L), peak mole fraction of key radicals, and flame instability of NH 3 –H 2 -Air flames are simulated in Chemkin Pro-software using the Mathieu and Petersen mechanism. The results show that the relatively low equivalence ratio and initial temperature promote the structural changes of the flame tip, forming a "tulip" flame and a distorted "tulip". As the equivalence ratio increases, the flame front speed and overpressure increase and the flame oscillates slightly. The distortion in the lip of the "tulip" is more pronounced. The increase in temperature promotes flame propagation in the early stages and the pressure decreases. Reactive activity increases with increasing temperature, the peak mole fraction of NH 2 and H radicals increases, and S L increases. At normal temperature, the flame is affected by thermo-diffusive instability only when lean mixture. The Darrieus-Landau instability increases as the equivalence ratio increases. Conversely, the Darrieus-Landau instability decreases with increasing temperature. Therefore, the current experimental and simulation results help to understand the laminar combustion characteristics of NH 3 –H 2 -Air at high temperatures. • The distortion of "tulip" is most obvious at T u = 300 K and φ = 1.1. • Increased temperature promotes flame propagation in the finger-shaped phase. • As The temperature increases (300–450 K), the H and NH 2 mole fractions increase. • DL instability decreases with increasing initial gas temperature. [ABSTRACT FROM AUTHOR]

The effects of different initial temperatures (T = 300–500 K) and different hydrogen volume fractions (5%–20%) on the combustion characteristics of premixed syngas/air flames in rectangular tubes were investigated experimentally. A high-speed camera and pressure sensor were used to obtain flame propagation images and overpressure dynamics. The CHEMKIN-PRO model and GRI Mech 3.0 mechanism were used for simulation. The results show that the flame propagation speed increases with the initial temperature before the flame touches the wall, while the opposite is true after the flame touches the wall. The increase in initial temperature leads to the increase in overpressure rise rate in the early flame propagation process, but the peak overpressure is reduced. The laminar burning velocity (LBV) and adiabatic flame temperature (AFT) increase with increasing initial temperature. The increase in initial temperature makes the peaks of H, O, and OH radicals increase. • The flame propagation time increases with the initial temperature. • The increase of initial temperature leads to faster propagation of early flame. • The peak overpressure decreases with increasing initial temperature. [ABSTRACT FROM AUTHOR]