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.

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Laminar flame speeds of n-butane/dimethyl ether (DME)−air mixtures were first measured using the outwardly expanding spherical flame and high-speed schlieren photography over a wide range of equivalence ratios, nitrogen dilution ratios, and DME blending ratios at elevated temperatures and pressures. The measured flame speeds were compared to the calculated flame speeds with some representative chemical kinetic models. Results show that laminar flame speeds of n-butane/DME blends slightly increase with the increase of the DME blending ratio. Reaction pathway analysis was performed, and the effect of the DME blending ratio on the laminar flame speed was interpreted with the latest Aramco Mech 1.3 model. A correlation of the laminar flame speed of n-butane/DME blends as a function of the equivalence ratio, temperature, pressure, and DME blending ratio is provided.

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Laminar flame speeds of premixed dimethyl ether/hydrogen/air flames were measured in a constant volume bomb at different temperatures, equivalence ratios, and hydrogen blending ratios. Results reveal that laminar flame speeds increase with an increased hydrogen blending ratio and initial temperature. The Wang model and Zhao model both perform well in predicting laminar flame speeds of the blends. Furthermore, three different models for an effective Lewis number are validated, and the volume-fraction-weighted model performs well in predicting the Markstein length. The effects of hydrogen addition on the flame speed and Markstein length of fuel blends are systematically studied. The chemical kinetic effect induced by hydrogen addition plays a dominant role in increasing the laminar flame speed in comparison to thermal and diffusive effects. In addition, there exists a critical equivalence ratio in the trend of the Markstein length. At the equivalence ratio less than the critical equivalence ratio, the Markstein length decreases with increased hydrogen fraction, indicating that the addition of hydrogen enhances the diffusional thermal instability of the blends. While at the equivalence ratio larger than the critical equivalence ratio, the Markstein length increases with the increase of the hydrogen mole fraction. Finally, the combined parameter [Ze(Le −1)] can reflect the trend of L b , which varies with the hydrogen blending ratio.