Experimental and numerical study of laminar premixed dimethyl ether/methane–air flame

• We investigate DME addition effect on flame speed, flame structure, Markstein lengths and flame instability of methane.
• Laminar flame speeds are measured at different temperatures, pressures, dilutions and DME blending ratios.
• Markstein lengths are presented under different DME blending ratios.
• Formaldehyde, methyl radical and formyl radical play an important role in the high temperature DME oxidation.

Laminar flame speeds of dimethyl ether/methane–air mixtures were measured in a constant volume combustion vessel at different initial temperatures (303–453 K), initial pressures (0.1–0.7 MPa), dilution ratios (0–25%), equivalence ratios (0.7–1.6) and over wide range of DME blending ratios (0–100%). Markstein lengths were also obtained at different blending ratios and equivalence ratios. Zhao DME model and NUIG Aramco Mech 1.3 were used to predict laminar flame speeds under the experimental conditions for the validation of the two kinetic models. Results show that laminar flame speeds increase almost linearly with the increase of DME blending ratio and the decrease of dilution ratio. The sensitivity coefficients of pressure are decreased with the increase of the blending ratios of DME. The simulated results of Zhao model agree well with the experimental data and those of previous studies, whereas the predicted results of NUIG Aramco Mech 1.3 give over-predictions especially at fuel-rich mixtures. Large increase in formaldehyde and small increase in methyl are resulted from the increase of DME. The laminar flame speed is found to have the linear correlation with H + OH mole fraction at maximum H mole fraction position. The unburned and burned gases Markstein length exhibit the similar trend and do not change monotonically with the increase of equivalence ratio for the mixtures with 20% DME addition. The intrinsic hydrodynamic instability is increased with the increase of DME blending ratio.