Laser-based speciation and kinetic analysis of N₂O–ethanol (NOEL) combustion in shock tube experiments

Hydrocarbon–nitrous oxide (HyNO_x) and related N₂O-based propellant systems are promising next-generation green propulsion alternatives owing to their high performance, low toxicity, and being self-pressurizing oxidizers. Among these, N₂O–ethanol (NOEL) mixtures represent a promising bipropellant combination offering clean combustion and compatibility with sustainable fuel production. This paper presents the first time-resolved measurements of CO and CO₂ formation during the high-temperature reaction of ethanol with N₂O behind reflected shock waves, offering insights into the kinetics of this promising green propellant system. Experiments were performed in a stainless-steel shock tube over 1300–2000 K at ∼ 1.3 atm and equivalence ratios of 0.5–2.0. Mid-infrared laser absorption diagnostics using quantum-cascade lasers enabled measurement of the time-resolved species. The results revealed rapid CO buildup, followed by oxidation to CO₂, characteristic of fast O/OH radical generation from N₂O decomposition and its reaction with H-atom. Comparisons with recent kinetic mechanisms showed that, although the models captured overall temperature and mixture dependence, they systematically misrepresented CO yields and peak timing, particularly at low to intermediate temperatures. CO time histories exhibited two-stage behavior, with an initial steep rise attributed to rapid ethanol decomposition, followed by a nearly plateau region governed by oxidation of the remaining products. Sensitivity analysis showed that inclusion of the N₂O + CO → N₂ + CO₂ reaction is critical for accurate CO prediction. An updated kinetic mechanism was therefore discussed, yielding superior CO predictions. Overall, this work provide time-resolved datasets that can be used as validation benchmarks for improving the kinetic modeling of hydrocarbon–N₂O combustion and HyNO_x-based propellant systems.