Characterizing the interaction of N₂O and CO with and without hydrogen addition using outwardly propagating spherical flames

Nitrous oxide (N₂O) is the third most important long-lived greenhouse gas and plays a role as the principal source of stratospheric nitric oxide, as well as the major scavenger of ozone. The flames of N₂O and CO/H₂/hydrocarbons play a crucial role in the combustion of nitramine-based solid rocket propellants and energetic materials. Nowadays, the utilization of NH₃ as a fuel underscores the need to reduce N₂O emission under flame conditions. Therefore, there is a need to understand the interaction between N₂O and low-carbon fuels, especially carbon monoxide and hydrogen. This study pioneers the utilization of outwardly propagating spherical flame method to investigate the laminar flame propagation of CO/N₂O mixtures at the initial pressure (P_u) of 2 atm, initial temperature (T_u) of 298 K and 0.6 < ϕ < 1.8. Additionally, the study delves into the interaction of N₂O and CO in the presence of H₂, examining the CO/H₂/N₂O/N₂ flame under similar conditions. Unlike CO/O₂ system, successful hydrogenic-free CO spherical flame propagation with N₂O as oxidizer was demonstrated. LBVs of “dry” CO/N₂O and CO/N₂O/N₂ flames within the closed combustion vessel of this study were found to be substantially lower than previously reported results using an open Bunsen-type flame, i.e., the literature reported LBVs of 50 % CO/50 % N₂O flames is 3.3–4.5 times higher than the currently measured value. The measured LBVs underscore the necessity for further examination of the rate of the controversial radical exchange reaction CO + N₂O=CO₂ + N₂ (R1). Recommended rates constant with activation energy of 43 kcal/mol were based on current evaluations and measurements. Comparison of the measured data with the predictions of literature kinetic models reveals the inadequacy of existing models. The proposed model, featuring an updated CO/H₂/N₂O subset, enhances predictability and highlights the intricate chemistry.