Ignition delay characteristics of ethanol in nitrous oxide atmosphere: Shock tube experiments and numerical investigation

Nitrous oxide (N₂O) and ethanol (C₂H₅OH) are green propellants that have great potential in propulsion systems. This study reports the experimental measurements of ignition delay times (IDTs) for N₂O/C₂H₅OH mixtures utilizing a shock tube. The influences of the pressure, equivalence ratio, and temperature on IDTs are evaluated within the pressure of 2.5 to 7.5 atm, equivalence ratio of 0.5 to 2.0 and temperature of 1300 to 1914 K. The measured IDTs exhibit an Arrhenius-type temperature dependence and decrease with elevated pressures. Conversely, transitioning from fuel-lean to fuel-rich conditions significantly prolongs the IDTs, with the equivalence ratio exerting a more pronounced influence than pressure. Furthermore, these IDTs are substantially longer than those observed in conventional O₂ atmospheres. Several established kinetic models are evaluated, culminating in the development and validation of a revised Shrestha mechanism that demonstrates substantially improved predictive accuracy. Subsequent sensitivity analyses reveal that the global reactivity is mainly driven by the highly endothermic unimolecular decomposition N₂O (+M) = N₂ + O (+M) and the reaction N₂O + H = N₂ + OH, while ethanol decomposition acts as principal ignition inhibitor. Rate of production and reaction pathway analyses further demonstrate that the drastically extended ignition delay stems from the absence of highly efficient chain-branching steps. Under fuel-rich conditions, intermediate fragments aggressively scavenge the limited radical pool, forcing a thermally-driven induction period. Furthermore, integrated reaction flux analysis elucidates the kinetic origins of high-pressure discrepancies, revealing that elevated pressures competitively dissipate the active radical flux. This work provides essential experimental data and a validated chemical kinetic model to support further engineering applications of N₂O/C₂H₅OH mixtures.