Significance of reaction CH3 + NO = H2CN + OH in two-stage ignition of nitromethane

Abstract Two-stage ignition of nitromethane diluted in Ar is investigated at various equivalence ratios (0.2–0.5), dilution levels (93%–97%), and pressures (4–16 atm) with a heated shock tube apparatus. OH* emission profiles are used to determine ignition delay times. The second-stage ignition delay time increases with increasing equivalence ratio or dilution level, but is insensitive to pressure especially at high dilution levels. The first-stage ignition delay time is unaffected by the present experimental parameters above 1150 K, below which it decreases with increasing equivalence ratio or pressure. An updated model reconsidering reaction CH3 + NO = H2CN + OH is examined against the experimental measurements from present work and literature, including ignition delay times, laminar burning velocities, and species mole fraction profiles. At fuel-rich condition, this reaction has a significant contribution to the formation of OH radical during the second-stage ignition. The two-stage ignition and intensity evolution of OH peaks are well predicted and explained kinetically by the updated model.