Ammonia, which does not emit carbon dioxide even when it is burned, is expected as a new carbon-free fuel to replace coal and natural gas used in thermal power plant. However, the turbulent flame propagation characteristics have yet to be extensively investigated. This study aimed to clarify the extinction limits of ammonia/air flame in turbulent fields. To achieve this aim, the spherical flame propagation experiments using a fan-stirred constant volume vessel were conducted.The results revealed the unique feature of extinction limit of ammonia in a turbulent field. The ammonia/air mixture with a 0.9 equivalence ratio can propagate at the highest turbulence intensity even though the laminar burning velocity reaches a maximum around an equivalence ratio of 1.1. The fuel-lean mixture can propagate at high turbulence intensity because of the effect of Lewis number. For a lean ammonia/air mixture that has a Lewis number smaller than unity, the local burning velocity increases by the diffusional-thermal instability. On the other hand, the local burning velocity in rich ammonia/air mixtures with a Lewis number larger than unity did not increase in the turbulent field, and the flame was easily extinguished. Because of the diffusional-thermal instability, the turbulence Karlovitz number at the flame extinction limit increases as the Markstein number decreases. The obtained findings from this study can contribute to the optimal design of gas turbines fueled by ammonia as well as the safety use of ammonia.

This study aimed to clarify the effects of turbulence intensity and coal concentration on the spherical turbulent flame propagation of a pulverized coal particle cloud. A unique experimental apparatus was developed in which coal particles can be dispersed homogeneously in a turbulent flow field generated by two fans. Experiments of spherical turbulent flame propagation of pulverized coal particle clouds in a constant volume spherical chamber in various turbulence intensities and coal concentrations were conducted using the new experimental apparatus. A common bituminous coal was used in this study.Flame propagation velocity was obtained based on the analysis of flame propagation images taken using a high-speed camera. It was found that the flame propagation velocity increased with increasing flame radius. For various turbulence intensities, the flame propagation velocity increases as the turbulence intensity increases. Similar trends were observed in spherical flames using gaseous fuel.The coal concentration has a weak effect on the flame propagation velocity, which is a feature that is unique to pulverized coal flames in a turbulent field. Experimental results of a spherical flame propagation behavior of turbulent pulverized coal particle cloud have been reported for the first time.The results obtained in this study are obviously different from previous pulverized coal combustion studies and any other results of gaseous fuel combustion research.

No abstract

No abstract