Effect of NO ₂ on ignition characteristics of methanol and chemical kinetics analysis

Based on the shock tube experiments, the influence of NO2 on the ignition characteristics of methanol fuel was systematically studied. The ignition delay time of the CH3OH/NO2/O2/Ar mixture with equivalence ratios of 0.5, 1, and 1.5 was measured at the reflected shock temperatures of 1100 ~ 1650 K and the reflected shock pressure of 0.20 MPa. The methanol–NO2 mechanism was newly constructed based on previously developed mechanisms for methanol and NO2 reaction pathways. The new combined reduced mechanism could well predict the ignition delay time of the CH3OH/NO2/O2/Ar mixture. Based on the newly constructed methanol–NO2 mechanism, the reaction path, sensitivity, and important elementary reactions of the stoichiometric mixture were analyzed, and the reasons why NO2 promoted the ignition of methanol fuel were found out: the increase of OH radicals generation and rapid accumulation in the early ignition stage enhanced the activity of the reaction system, interfered the ignition process of CH3OH/NO2/O2/Ar mixture in advance, and promoted the ignition of methanol fuel.