Kinetic modelling of the ignition delays in monomethylhydrazine/hydrogen/oxygen/argon gaseous mixtures

The objective of this study is to estimate the efficiency of ignition promotion or inhibition for H₂/O₂/Ar mixtures by monomethylhydrazine (CHjNHNHa, noted MMH), a propellant widely used in rocket propulsion systems. This is accomplished by computations performed with a detailed kinetic model. The model is validated with experimental ignition delays obtained behind a reflected shock wave in mixtures of MMH/O₂/Ar, MMH/O₂/H₂/Ar and H₂/O₂/Ar. Good agreement (to about 25 per cent) is obtained between experimental and computed ignition delays with the mixtures of MMH/H₂/O₂/Ar at high temperatures (900-1170 K), in the pressure range 225-414 kPa. For the mixtures of H₂/O₂/Ar the agreement is also good over a very large range of temperatures (960-2300 K), pressures (up 5 MPa) and compositions (from highly diluted mixtures to undiluted). This model shows that, for the mixtures under consideration, MMH added in relatively small amounts (up to 10 per cent with respect to hydrogen) is an inhibitor or a promoter, depending on the amount added, under 1000 K and an inhibitor above 1000 K.