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

Abstract

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 (ST) of four butanol isomers are determined, compared, and analyzed in detail. A unified scaling of ST is presented to consider the effects of molecular transport, during which different mathematical correlations are evaluated and modified. Results show that ST is increased with u’ and P. The maximum ST will shift to richer side compared to laminar condition, and the shifting trend will be more evident at high u’. The order of ST between four butanol isomers is similar to that of laminar burning velocity (SL) and it is: n-butanol > i-butanol≈s-butanol > t-butanol. The discrepancy in ST is mainly induced by SL, while turbulence stretch and flame intrinsic instability play an amplifying role. Turbulent Reynolds number (ReT), 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 ST 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 ST correlations for a wide range of conditions.