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Experimental and dynamic analyses of the deflagration characteristics of laminar premixed syngas-air at different preheating temperatures and with different CO 2 volume fractions were carried out in a rectangular half-open pipe. The effects of CO 2 concentration and different initial temperatures on the flame structure evolution, flame structure profile and reaction rate of critical radicals, flame propagation speed, overpressure dynamics and hydrodynamic instability of syngas-air mixture were studied. The FFCM-1 mechanism was used to predict the laminar burning velocity of syngas-air under relevant conditions. The results revealed that the addition of CO 2 inhibited the flame propagation and reduced the concentration of H, OH and O, thus reduced the laminar burning velocity. The increase in temperature promotes the chemical effect of CO 2 , and the interaction between the flame front and the pressure wave is more pronounced, prolonging the duration of the " tulip " flame. Adding CO 2 reduces the flame front speed and overpressure, decreases the oscillation amplitude in late flame propagation, and inhibits the explosion intensity. Meanwhile, the temperature increase accelerates the flame propagation in the spherical and finger stages, and the maximum flame propagation speed and peak pressure appear earlier. In addition, as CO 2 content and temperature rise, flame hydrodynamic instability is difficult to ignore. However, there is a lack of data from studies of syngas deflagration dynamics at higher temperatures and with higher CO 2 additions. This suggests a focus on studies at higher temperatures as well as with higher CO 2 additions to enable the development of accurate kinetic models for wide range of syngas combustion. Also, the higher the initial temperature, the longer the time required for heating. • The appearance time of the tulip flame increased with the initial temperature. • CO 2 inhibits flame propagation and reduces the concentration of H, OH and O. • The maximum flame front speed appear earlier as the initial temperature increases. • The peak pressure decreases with increasing initial temperature. [ABSTRACT FROM AUTHOR]

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]