Measurement on instantaneous flame front structure of turbulent premixed CH₄/H₂/air flames

Instantaneous flame front structure of turbulent premixed CH₄/H₂/air flames (hydrogen fraction of 0%, 5%, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner. Hot wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous flame front structure, respectively. Turbulent burning velocity, S_T, flame surface density, σ, and mean flame volume, V_f, were calculated by processing the OH-PLIF images. Results show that the flame front structures of the turbulent premixed flames are the wrinkled flame front and it becomes much finer with the increase of turbulence intensity as well as hydrogen fraction. The value of S_T/S_L significantly increases with the increase of u'/S_L and it slightly increases with the increase of hydrogen fraction. Flame surface density profile are symmetric and gives its maximum value at about c=0.5. Hydrogen addition slightly enhances the σ and the tendency is more obvious under higher turbulence intensity. The decrease of σ with the increase of turbulence intensity is mainly due to the effect of flame volume. The mean flame volume of flame region obviously increases with the increase of turbulence intensity within the experimental range due to the increase in depth of the large scale flame wrinkles and flame height. Hydrogen addition is not a predominant factor within the hydrogen fraction range in this study.