The ignition temperatures of nitrogen-diluted mixtures of methane and ethylene were measured by conterflowing heated air up to 3atms. In addition, the laminar flame speeds of air, methane and ethylene mixtures were obtained in the conterflow system under atmospheric pressure, for extensive ranges of lean-to-rich equivalence ratio. These experimental data, relevant to low-temperature ignition chemistry and high-temperature flame chemistry, were subsequently compared with calculations using two detailed ethylene mechanisms consisting of 70 and 75 species respectively. Sensitivity and Computational Singular Perturbation (CSP) analyses were applied to identify the role of ethylene addition in facilitating nonpremixed ignition and promoting premixed flame propagation. Furthermore, by studying the ignition response and flame propagation of these mixtures of hydrocarbons of the same family but with quite different reactivities, the hierarchical nature of the associated oxidation kinetics was assessed. This issue was further examined by comparing the sizes of the reduced mechanisms of the pure fuels and their mixtures.