High-pressure oxidation of hydrogen diluted in N₂ with added H₂O or CO₂ at 100 atm in a supercritical-pressure jet-stirred reactor

The oxidation of H₂ diluted in N₂ with and without 10 % H₂O or 20 % CO₂ additions are studied at fuel-lean conditions at 100 atm and 500–1000 K in a supercritical-pressure jet-stirred reactor. The mole fractions of H₂ and O₂ are quantified by using micro-gas chromatography (µ-GC). Experiment shows that H₂ oxidation is inhibited at lower temperatures (850–950 K) while it is promoted at higher temperatures (950–1050 K) with 10 % H₂O additions or 20 % CO₂ additions. In addition, the effect of H₂O is more significant than that of CO₂. Five models are employed in simulations of the observables. Unfortunately, all of these models fail to capture the effect of H₂O and CO₂ additions on H₂ oxidation. Pathway and sensitivity analyses of H₂ show that the reactions of H + O₂ + (M) = HO₂ + (M) and H₂O₂ + (M) = 2OH + (M) dominate the radical production (HO₂ and OH) and H₂ oxidation at 100 atm. A further perturbation of pre-exponential coefficients and collisional factors of these reactions indicates that collisional factors of H₂O and CO₂ have small effect under the experimental conditions, while a smaller reaction rate for H₂O₂ + (M) = 2OH + (M) may explain the inhibiting effect of H₂O and CO₂ additions at lower temperatures. Real-fluid corrections on intermolecular interactions and mixing rules should be further investigated to explain the effect of H₂O and CO₂ additions.