Effect of Steam Dilution on the Structure and Stabilization of Lifted Flames of Hydrogen

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Abstract

<p>Non-premixed lifted flames of hydrogen are investigated using direct numerical simulations. Initially, a laminar non-premixed flame of hydrogen and steam diluted oxygen is compared with a nitrogen diluted oxygen case to investigate the effect of steam dilution on the structure and stabilization mechanism of the lifted flames. Both cases result in a triple flame structure, typical of non-premixed lifted flames. The diffusion and lean premixed branches of these flames are observed to collide due to the high diffusivity of hydrogen. Even though the overall structure of both cases is similar, the cases showed some variations in their species distributions. Further analyses showed that these variations result from steam dilution, altering the rate of certain reactions. The stabilization mechanism of the flames is investigated using transport budget analyses. In the steam diluted case, the diffusion and reaction terms have the same order of magnitude, indicating flame propagation stabilization, whereas the reaction term is dominant for the nitrogen diluted case, indicating autoignition stabilization. The results suggest that even though the overall structure of the nitrogen diluted and steam diluted flames is the same, the effect of steam dilution on the rates of reactions may alter the stabilization mechanism. Then, the effect of pressure on the flame features of the steam diluted case is investigated at four different pressures varying from 2-20 atm. The results of the cases at higher pressures suggest that neither the overall structure nor the stabilization mechanism of the flames is affected by the pressure.</p>

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