Abstract:

In order to meet high-performance propulsion system requirements for aerospace technology and severe future restrictions on hydrazine use, research on non-toxic, high-performance, and low-cost propulsion technology is urgently needed. The N₂O-C₂ hydrocarbon monopropellant NOFBX (Nitrous Oxide Fuel Blend) provides significant benefits for meeting these criteria and has become a focus of increased research in recent years. In this study, a chemical kinetic model for NOFBX combustion that integrates the reduced C₂ sub-mechanism, the N₂O sub-mechanism in the literature, and the N₂O/CH species reaction mechanism has been developed. The present mechanism consists of 52 species and 325 elementary reactions. For better predictions of ignition and combustion characteristics, the kinetic parameters of the sensitive reactions with comparatively high rate constant uncertainties have been revised. The present model has been validated against published experimental data, including flow reactor results on N₂O/H₂O/N₂ mixture decomposition, shock tube ignition delay times on N₂O/C₂ hydrocarbons diluted with N₂ or Ar mixtures, heat flux of flat flame laminar flame speeds on N₂O/C₂H₂ diluted with N₂ mixtures, and Bunsen flame laminar flame speeds on N₂O/C₂H₄ diluted with N₂ mixtures. Additionally, this study compares the new model to other published small hydrocarbon fuel kinetic models with a NO_x sub-mechanism. The experimental validations show that the present model accurately captures the nitrous oxide decomposition process and precisely predicts N₂O, O₂, NO, and NO₂ vital species concentration distributions. For all N₂O-C₂ hydrocarbon fuel systems (ethane-, ethylene-, and acetylene-nitrous oxide), the ignition delay times predicted by the present model are in good agreement with the experimental data. Furthermore, at a wider range of initial temperatures (1100-1700 K), initial pressures (0.1-1.6 MPa), and equivalence ratios (0.5-2.0) for the ignition delay times of ethylene-nitrous oxide, the present model exhibits improved predictions of experimental data. For the laminar flame speeds of N₂O-C₂H₂ and N₂O-C₂H₄ mixtures, the present model generally exhibits satisfactory predictions of the experimental data over the whole range of equivalence ratios (0.6-2.0). However, at initial pressure 0.1 MPa and equivalence ratios of 1.0-1.6 for N₂O-C₂H₄ laminar flame speeds, the present model slightly underestimates experimental data. Considering the much higher uncertainty of the measured laminar flame speeds by the Bunsen flame method, this discrepancy is acceptable. Due to the small scale, full experimental validations and good applicability, the present model can be used to further research on multi-dimensional combustion simulation in NOFBX engine combustors.

Key words: Nitrous, Small hydrocarbons, Chemical mechanism, Ignition delay time, Green propellant