Influence of local flame displacement velocity on turbulent burning velocity

In our previous works, the mean local burning velocity turned out to be changed from the original laminar burning velocity due to the preferential diffusion effect, and it was found to be an important factor dominating the turbulent burning velocity The present study investigates directly the local flame propagation properties of methane, propane, and hydrogen premixed turbulent flames in the weak turbulence region. A laser tomography technique is used to obtain the temporal local flame configuration and movement in a constant-volume vessel, and quantitative analyses are performed. The local flame-front curvature and the local flame displacement velocity SF are quantitatively obtained as the key parameters of the turbulent combustion. First, the observation of sequential flame tomograms shows that the turbulent flame front seems to be classified into active and inactive parts depending on its geometric configuration. Next, the values Of SF are found to be distributed over a wide range and to be dependent on the local curvature of the turbulent flame. In addition, the values of SF for the methane and hydrogen mixtures have a tendency to become larger with decreasing equivalence ratio, whereas those for the propane mixture become smaller. We discuss also the influence of preferential diffusion and Markstein number on the local flame displacement velocity.