This study is performed to investigate directly the local flame properties of turbulent propagating flames at the same weak turbulence condition (u′/SL0 = 1.4), in order to clarify basically the influence of the addition of hydrogen to methane or propane mixtures on its local burning velocity. The mixtures having nearly the same laminar burning velocity with different rates of addition of hydrogen δH are prepared. A two-dimensional sequential laser tomography technique is used to obtain the relationship between the flame shape and the flame displacement. The local flame displacement velocity SF is quantitatively obtained as the key parameters of the turbulent combustion. Additionally, the Markstein number Ma was obtained from outwardly propagating spherical laminar flames, in order to examine the effects of positive stretch and curvature on burning velocity. It was found that the trends of the mean values of measured SF with respect to δH, the total equivalence ratio Φ and fuel types corresponded well its turbulent burning velocity. The trend of the obtained Ma could explain the local burning velocity of turbulent flames only qualitatively. Based on the Ma, the local burning velocity at the part of turbulent flames with positive stretch and curvature, SLt, is estimated quantitatively. As a result, a quantitative relationship between the estimated SLt and the SF at positive stretch and curvature of turbulent flames could be observed for mixtures with increasing the Lewis number.
Effect of Stretch on Local Burning Velocity of Premixed Turbulent Flames
