Experimental study on combustion characteristics of N₂-diluted diethyl ether-air mixtures

Combustion characteristics of diethyl ether-air-N₂ diluent are studied at different initial temperatures, equivalence ratios, and dilution ratios using an outwardly expanding spherically flame and high-speed schlieren photography system. The effects of these parameters on laminar burning velocity, Markstein length, and Zeldovich number are analyzed. The results show that laminar burning velocity is increased with the increase of the initial temperature and is decreased with the increase of the dilution ratio. The maximum value of the laminar burning velocity is presented at the equivalence ratio of 1.0. The Markstein length is decreased with the increase of the initial temperature and equivalence ratio. Except for the equivalence ratio of 1.2, the Markstein length is increased with the increase of the dilution ratio, indicating that the increase of the initial temperature and equivalence ratio enhances the diffusional-thermal instability of the flame front but the increase of the dilution ratio reduces the diffusional-thermal instability. The density ratio is decreased, and the flame thickness is increased with the increase of the dilution ratio, indicating that the hydrodynamic instability is suppressed. The Zeldovich number is increased with the increase of the dilution ratio and is decreased with the increase of the initial temperature. The Zeldovich number gives the lowest value at the equivalence ratio of 1.0, where the adiabatic temperature gives the maximum value. A formula of laminar flame velocity is correlated with initial conditions based on the experimental data.