Laminar Flame Characteristics of iso-Octane/n-Butanol Blend-Air Mixtures at Elevated Temperatures

摘要

In this work, laminar flame speeds and Markstein lengths of iso-octane/n-butanol-air mixtures were measured via the outwardly expanding spherical flame method and high-speed schlieren photography over a wide range of equivalence ratios and blending ratios of n-butanol at elevated initial temperatures. Results show that laminar flame speeds of fuel blends slightly increase with increasing blending ratio of n-butanol. The effect of blending ratio on laminar flame speed of fuel blends was mechanistically interpreted through examining the thermodynamic and diffusive property, as well as the overall oxidation kinetics. Measurements on the burned gas Markstein length show a generalized behavior. There exists a minimum absolute Markstein length at the critical equivalence ratio Φ*, under which the stretch effect on the flame propagating speed is minimized. At equivalence ratios less than Φ*, Markstein length is decreased with increasing blending ratio of n-butanol, indicating that the addition of n-butanol reduces the diffusional thermal stability of the blend; while at equivalence ratios larger than Φ*, Markstein length increases with increasing blending ratio of n-butanol. This experimental observation on the Markstein length is consistent with the theoretical investigation. A correlation of laminar flame speed of n-butanol/iso-octane blend as a function of equivalence ratio, temperature, and blending ratio of n-butanol is given on the basis of experimental data.