Unsteady flamelet modeling for N[formula omitted]H[formula omitted]/N[formula omitted]O[formula omitted] flame accompanied by hypergolic ignition and thermal decomposition

Abstract

In this study, the applicability of the flamelet approach to numerical simulations of hydrazine (N2H4)/nitrogen tetroxide (NTO, N2O4) combustion, in which hypergolic ignition and thermal decomposition occur, is investigated in terms of two-dimensional numerical simulations of two types of N2H4/NTO jet flames, namely, the gaseous N2H4/NTO jet flame and the N2H4 spray jet flame in the gaseous NTO stream. In case of the gaseous jet flame, the numerical simulation is performed employing the unsteady flamelet/progress variable (UFPV) approach. In case of the spray jet flame, on the other hand, a non-adiabatic unsteady flamelet/progress variable (NAUFPV) approach, which combines the UFPV approach and the non-adiabatic flamelet/progress variable (NAFPV) approach, is proposed. The validity of these and some other existing flamelet approaches is investigated by comparison with the results obtained using the exact approach, in which detailed chemical reactions are directly solved. The results show that the UFPV and NAUFPV approaches drastically improve predictions of the N2H4/NTO gaseous and spray combustion behavior, respectively, including the ignition process, the flame lift-off height, and the distributions of temperature and chemical species concentrations. This indicates that self-decomposition flame of fuel is successfully captured by the UFPV approach, and that the NAUFPV approach can additionally take into account the heat loss effect due to evaporation of droplets.