Impact of Dilution on Laminar Burning Characteristics of Premixed Methane-Dissociated Methanol-Air Mixtures

A constant volume combustion vessel is employed to investigate the impact of different diluents and diluent gas fractions on the methane-dissociated methanol-diluent-air premixed flames at 0.3 MPa and 343 K. The diluent gas causes the adiabatic flame temperature and thermal diffusivity to decrease, which is the main reason for the decreased laminar burning velocity, and carbon dioxide exhibits a stronger inhibitory effect than nitrogen. With increasing diluent gas fraction, the diffusive-thermal instability is enhanced while the hydrodynamic instability is inhibited, these two factors are the main reason for the insensitivity of the flame instability to the diluent gas fraction. Further, flame instability is not sensitive to the diluent gas type. R38 is the dominant chain branching reaction, while R35 and R52 are the dominant chain termination reactions in the combustion process. With the increase in the diluent gas fraction, the rates of the dominant chain termination reactions shows greater inhibition of laminar burning velocity, a larger decrease in the chain branching reaction rate, and a smaller decrease in the chain termination reaction rate will significantly reduce the free radical concentration. The maximum reaction rate reduction when diluted by carbon dioxide is greater than when diluted by nitrogen.