Unravelling the unique kinetic interactions between N2O and unsaturated hydrocarbons

Abstract: The interaction between unsaturated hydrocarbons and N2O has attracted considerable attention in recent years due to their important roles as potential propellants for advanced propulsion systems e.g. NOFBX, key combustion intermediates in EGR systems, and as major pollutants and precursors in atmospheric chemistry. Although experimental studies and kinetic models have been developed to investigate its fuel chemistry, discrepancies remain between modeled and measured ignition delay times at low temperatures. In this work, we characterize previously unreported direct interaction pathways between N2O and unsaturated hydrocarbons C2H4, C3H6, C2H2, and C3H4 through quantum chemistry calculations, comprehensive kinetic modeling, and experimental validation. These reactions proceed via O-atom addition from N2O to unsaturated hydrocarbons, forming five membered ring intermediates that decompose into N2 and hydrocarbon specific products. Distinct mechanistic differences are identified between alkenes and alkynes, arising from the disparity in N C bond lengths within the intermediates 1.480 A vs. 1.381 A, which governs their decomposition pathways. The corresponding rate coefficients are determined and implemented into multiple kinetic models, with autoignition simulations showing a pronounced promoting effect on model reactivity and improved agreement with experiments, especially at low temperatures. Flux analysis further reveals that the new pathways suppress conventional inhibiting channels while enabling aldehyde and ketone forming pathways that enhance overall reactivity. This work provides a more complete description of N2O hydrocarbon interactions, advancing predictive capability for combustion and atmospheric chemistry.