Theoretical study of the second- and third-H-abstraction reactions of monomethylhydrazine and nitrogen dioxide and its application to hypergolic ignition modeling

Abstract

The chemical kinetics of the second–H-abstraction and the third-H-abstraction reactions of monomethylhydrazine (MMH) and nitrogen dioxide (NO2) and its application to modeling hypergolic ignition of MMH/NO2 were investigated in this work. Potential energy surfaces (PESs) for the key reactions were obtained by employing the CCSD(T)/CBS//M06-2X/6-311++G(d,p) single-reference method and the MRCI(7e,6o)/CBS//M06-2X/6-311++G(d,p) multi-reference method. The RRKM/Master Equation approach was used to calculate the temperature- and pressure-dependent rate constants. For the second-H-abstraction reactions, the trans-CH3NNH and HNO2/HONO are the major products. For the third-H-abstraction reactions, the bimolecular reaction of cis-CH3NNH+NO2→CH3NN+HNO2 is more favorable. The calculated rate constants and thermodynamics data were fitted and incorporated into two existing mechanisms to investigate their influence on modeling MMH/NO2 hypergolic ignition. The modeling results show that the system reactivity of MMH/NO2 is promoted by the second- and third-H-abstraction reactions, as the ignition delay times decrease by a factor of two at 300–800 K. The production rate and sensitivity analyses further validate the significance of the second-H-abstraction reactions at low temperatures. The sensitivity analyses at 1000 K also indicate the necessity of further investigations on CH2O, N2H2/NO2, and CH3NH/NO2 sub-mechanisms for modeling the MMH/NO2 combustion at high temperatures. This work provides not only new kinetic and thermochemical data but also a better understanding of the hypergolic ignition of MMH/NO2.