Experimental and kinetic modeling study of laminar flame characteristics of higher mixed alcohols

Mixtures of alcohols combining strengths of lower and higher alcohols show promising alternative properties as engine fuel. To aid the extensive application of the mixed alcohols, detailed combustion investigation is necessary. In this study, laminar flame speeds and Markstein lengths were measured for simplified higher mixed alcohols (blends of methanol and n-hexanol/n-heptanol/n-octanol) with spherically propagating flame at 0.1 MPa, elevated temperature of 433 K, and different mixing ratios. A comprehensive model was developed to describe the high temperature chemistry of the mixed alcohols. The accuracy of the model was validated with present data. Results reveal that the three higher alcohols exhibited close laminar flame speeds and Markstein lengths resulting from their similar thermal, diffusion, and chemical kinetic properties. With the increasing mixing ratio of the higher alcohols, the laminar flame speed decreased, especially for the rich mixtures. The maximum laminar flame speed slightly shifted to the lean side. The Markstein length increased at extremely lean mixtures and decreased at extremely rich mixtures, with the intersection occurring at the equivalence ratio between 1.2 and 1.3. The laminar flame speed variation of the mixed alcohols was dominated by chemical kinetics. Reaction pathway analyses indicated that the cracking process of each component in the mixed alcohols remains as that in the pure alcohols. Such result demonstrated the chemical kinetic effect resulting from changes in fuel components.