2009 Volume 4 Issue 1 Pages 190-201
This experimental 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 lean and rich 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 in a constant-volume vessel. Some of the key parameters of local flame properties quantitatively measured are the local flame displacement velocity SF, curvature and stretch of turbulent flames. Additionally, the Markstein number Ma was obtained from outwardly propagating spherical laminar flames, in order to examine the effect of positive stretch 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 SF of turbulent flames only qualitatively. The local burning velocity at the part of turbulent flames with positive stretch and curvature using this Ma, SLt, attempted to be 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 only for mixtures with Le > 1 or Ma >0.
