Measurement of laminar burning velocities of dimethyl ether-air premixed mixtures with N₂ and CO₂ dilution

Measurements of laminar burning velocities of dimethyl ether-air premixed mixtures with N₂ and CO₂ dilution were made at room temperature and atmospheric pressure using the spherically expanding flame and schlieren photography over a wide range of dilution and equivalence ratios. The stretched flame propagation speed, the unstretched flame propagation speed, the unstretched laminar burning velocity, and the Markstein length (L_b) were obtained and analyzed. The results show that the flame speeds and the burning velocities decrease monotonously with the increase of the dilution ratio. The maximum value of the unstretched laminar burning velocity is presented at the equivalence ratio of 1.1, regardless of N₂ dilution ratios, while it slightly shifts to the rich mixture side with the increase of the CO₂ dilution ratio. This phenomenon reveals the different dilution effect on the unstretched laminar burning velocity between the triatomic molecule gas CO₂ and the diatomic molecule gas N ₂. The Markstein length increases with the increase of the dilution ratio. The addition of diluents to the stoichiometric and/or the lean mixture has a larger influence on the Markstein length compared to those of the rich mixture. The addition of diluents obviously enhances the stability of the flame front for the lean mixture, but the impact is slight for the rich mixture. The influence of CO₂ as the diluent on the flame speed and the flame stability is larger than that of N₂ as the diluent for dimethyl ether-air mixture combustion.