Effects of hydrogen addition on the laminar flame speed and markstein length of premixed dimethyl ether-air flames

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.