Turbulent burning velocity and its unified scaling of butanol isomers/air mixtures

Turbulent expanding flames of butanol isomers/air mixtures are investigated in a wide range of conditions (T = 393 K, P = 1, 2 bar, ϕ = 0.7, 1.0, 1.3 and u^’=0, 0.89, 1.77, 2.66 m/s). Turbulent burning velocity (S_T) of four butanol isomers are determined, compared, and analyzed in detail. A unified scaling of S_T is presented to consider the effects of molecular transport, during which different mathematical correlations are evaluated and modified. Results show that S_T is increased with u^’ and P. The maximum S_T will shift to richer side compared to laminar condition, and the shifting trend will be more evident at high u^’. The order of S_T between four butanol isomers is similar to that of laminar burning velocity (S_L) and it is: n-butanol > i-butanol≈s-butanol > t-butanol. The discrepancy in S_T is mainly induced by S_L, while turbulence stretch and flame intrinsic instability play an amplifying role. Turbulent Reynolds number (Re_T), Karlovitz number (Ka), and Kobayashi model can all give a reasonable correlation of current experimental data while an acceptable scatter exists in Damkohler number (Da) correlation. The primary S_T models are modified by Leⁿ and the value of n is unified to −0.35 for different correlations, which ensures the molecular transport effects at the quantitative level. It appears that these correlations are applicable for hydrocarbons and alcohols, which can be more simplified and suitable S_T correlations for a wide range of conditions.