Ignition of methane with hydrogen and dimethyl ether addition

Abstract

Premixed and non-premixed ignition of methane/hydrogen and methane/dimethyl ether (DME) binary fuel blends with hot air is studied through numerical simulation with detailed chemistry and variable thermodynamic and transport properties. The emphasis is spent on assessing the kinetic and transport effects involved in CH4 ignition enhancement caused by H2 and DME addition. Two configurations are considered: a premixed homogeneous configuration to examine the chemical kinetics and a non-premixed counterflow configuration to assess the transport effects. For the homogeneous ignition process, small amount of DME addition is found to be more effective than H2 addition in terms of promoting the ignition of CH4/air mixture. Sensitivity analysis and reaction path analysis are conducted and key elementary reactions involved in CH4 ignition enhancement by H2 and DME addition are identified. For the non-premixed ignition process, H2 addition is shown to be always more effective than DME addition in terms of CH4 ignition enhancement. It is found that the preferential mass diffusion of H2 over CH4 and that of CH4 over DME have great influence on the local blending ratio at the ignition kernel, which controls the non-premixed ignition process. Therefore, non-premixed ignition of binary fuel blends is significantly affected by the mass diffusivity of each fuel component. Moreover, the effects of strain rate on the non-premixed ignition of CH4/H2 and CH4/DME binary fuel blends with hot air are discussed.