Ignition delays in MMH+CH4+O-2+Ar mixtures

Ignition delays have been investigated for mixtures of monomethylhydrazine (MNH) + O-2 + CH4 + Ar at high temperature (907-1360 K) in the pressure ran ge 246-412 kPa. All measurements were performed in the reflected-shock regi on of a shock tube. Reaction progress was monitored via piezoelectric press ure transducers and UV absorption by MMH. In the composition range studied, the ignition delays tau can be correlated by the expression 7(mus) = 2.042 X 10(-2)[MMH](-0.87)[O-2](-2.09) [CH4](+0.68)[Ar](1.24) exp(8503/T) where the concentrations are expressed in moles m(-3). This study shows unambiguo usly that CH4 inhibits MMH + O-2 (+Ar) ignition. This inhibiting effect dep ends on the mixture composition (equivalence ratio in MMH, [MMH]/[CH4] rati o, etc.), on the temperature, and on the pressure. From a mechanistic point of view, methane is supposed to compete with MMH decomposition products fo r reaction with oxygen. The comparison between the CH4/O-2/Ar and CH4/MMH/O -2/Ar ignition delays leads to the conclusion that MMH can be used as a ign ition promoter in CH4/O-2 mixtures.