Development of scale-controlled premixed turbulent burner and the flame structure analysis

The structure-variable premixed turbulent burner is developed to investigate the effects of single turbulence parameters on flame structure, and to broaden turbulence intensity and scale range. Hot-wire anemometer measurements of cold flow indicate that the burner can utilize different geometry structures to produce scale-controlled flow field and realize the investigation of the effects of single turbulence parameters on flame structure. Fifteen representative structures were selected for the premixed turbulent combustion experiment. OH-PLIF images show that high turbulence intensity enhances flame surface wrinkling, as well as increasing the number of island structures. Data are reported at 1 < u'/S_{L, 0} < 10 for CH₄/air flames with equivalence ratio of 0.7 in the thin reaction zones. Increasing integral scale decreases the turbulent burning velocity at high Reynold number. There may exist a critical Re_c which can represent the degree of how inertial forces are dominant to determine the effect of the integral scale on the turbulent burning velocity. Increasing the integral scale can also enlarge the flame volume, due to larger vortex containing higher energy. However, intensive turbulence intensity can wrinkle the flame surface much more remarkably, resulting in superposition of small scales on large scales. Therefore, the increasing turbulence intensity increases the flame volume more significantly, covering up the impact of integral scale on flame volume. These results indicate that the effect of integral scale (represent large scale) on the flame heat release rate is less significant than the effect of turbulence intensity (represent superposition degree of small scales on large scales).