Hypergolic ignition and flame structures of hydrazine/nitrogen tetroxide co-flowing plane jets

Abstract

Hydrazine (N2H4)/nitrogen tetroxide (NTO) co-flowing plane jets were simulated to explore the hypergolic ignition processes and flame structures in N2H4/NTO bipropellant thrusters. The Navier–Stokes equations with a detailed chemical kinetics mechanism were solved in a manner of direct numerical simulation to reveal the influence of the distinct chemical reaction, i.e., hydrogen abstraction by nitrogen dioxide (NO2) and the thermal decomposition of N2H4. In the ignition processes, the hydrogen abstraction sequence played a significant role in preheating the mixture gases. Further, the ignition eventually occurred in the region where both N2H4 and NTO were sufficiently supplied for preheating. Hence, the ignition position and delay strongly depended on the fluid-mixing conditions. After the flames reached a steady state, the combustion flames uniquely comprised two types of flames, the outer diffusion flame and the inner decomposition flame. The outer diffusion flame came from the oxidization by NTO. The inner decomposition flame was caused and maintained by the heat transfer from the outer diffusion flame and a high rate of heat release from the thermal decomposition of N2H4. Because of the decomposition flame, the decomposition products such as NH3 and H2 were the major constituents of the downstream combustion gases.