Science and Technology of Energetic Materials

Vol.74, No.1 (2013)

Research paper

Origin of hypergolic ignition of N2H4/NO2 mixtures
Yu Daimon, Hiroshi Terashima, and Mitsuo Koshi


Hydrazine (N2H4) has a unique characteristic inducing hypergolic ignition even at very low temperatures with nitrogen dioxide (NO2). In order to understand the chemical kinetic origin of this hypergolic nature, thermochemical data (heat of formation, specific heat capacity, and entropy) for chemical species relevant to N2H4/NO2 combustion are firstly evaluated on the basis of quantum chemical calculation at the CBS-QB3 level of theory. Then, a preliminary detailed chemical kinetic mechanism for gas-phase combustion of N2H4/NO2 mixtures has been constructed. Kinetic simulations indicated that sequential reactions of N2Hm+NO2 (m=4,3,2,1), that is, N2H4+NO2=N2H3+HONO (1), N2H3+NO2=N2H3NO2=N2H2+HONO (2), N2H2+NO2=NNH+HONO (3), and NNH+NO2=N2+HONO (4), are responsible for the hypergolic ignition at low temperatures. Rate constants of these reactions were estimated based on the transition state theory and unimolecular rate theory. The proposed mechanism can predict low temperature ignition of N2H4/NO2mixtures. The origin of the low temperature ignition is the reaction sequence of hydrogen abstraction by NO2 from N2H4, N2H4=>N2H3=>N2H2=>NNH=>N2. Large amount of heat is released during this reaction sequence, especially by the reaction (4) which produces N2, and the resulting temperature rise accelerates the reaction (1), which has a small activation barrier.

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propellant, hypergolic, hydrazine, combustion, kinetics

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