A theoretical study on the mechanism of C₂H_3-5 oxidation by N₂O

Nitrous oxide fuel blend (NOFBX), consisting of nitrous oxide and small hydrocarbons like ethane and ethene, offers potential for green propellants and optimized propulsion systems. This study investigates the oxidation reaction pathways of N₂O with C₂H_3-5 using G4 and CCSD(T)/cc-pVQZ//M06-2X(D3)/def2-TZVP methods. The oxidation typically begins with addition reactions at N or O atomic sites, or the H-abstraction reaction by N₂O, followed by hydrogen transfer and bond dissociation, leading to stable molecules and free radicals. Additionally, RRKM/ME theory was applied to calculate the reaction rate constants and branching ratios for N₂O + C₂H_3-5 over a temperature range of 300-3000 K and pressures of 1-100 atm. A comparative analysis identified the dominant reaction pathways for N₂O with CH components. Simulations incorporating detailed reaction mechanisms and kinetic data improved predictions of ignition delay times for both N₂O/C₂H₄ and N₂O/C₂H₆ systems. The new model also shows higher/lower fuel conversion below/above ∼1000 K. Sensitivity analysis indicates that direct reactions between N₂O and CH components have minimal impact on model accuracy at temperatures above the ignition point, becoming stronger near ∼1200 K before weakening at higher temperatures. The results provide essential data for refining kinetic models of N₂O/C₂H₄ and N₂O/C₂H₆ systems and offer a theoretical basis for designing and optimizing NOFBX propellants.