reduction of n2o

[Joris Strassburg]

good day
i want to investigate how well n2o is degraded in a combustion exhaust gas. the reaction in a plugflow reactor gives me meaningful results. But if i look at the equilibrium composition, all n2o is degraded even under atmospheric conditions
i have tried to break down the equilibrium calculation as far as possible:

p = 1e5 # [Pa]
T = 300 # [K]
T_norm = 273 #[K]
x0_n2o = 10000e-6 # N2O in Air [mol/mol]

mix = ct.Solution("gri30.yaml")
mix.X = {"N2": 0.79*(1-x0_n2o), "O2": 0.11*(1-x0_n2o), "CO2":0.1*(1-x0_n2o), "N2O":x0_n2o}
mix.TP = T,ct.one_atm
mix.equilibrate("TP")
print(f "N2O ppm: {mix.X[mix.species_index('N2O')]*1e6:.6f}")
print(f "NO2 ppm: {mix.X[mix.species_index('NO2')]*1e6:.6f}")
print(f "NO ppm: {mix.X[mix.species_index('N2O')]*1e6:.6f}")
print(f "N2 mole fraction: {mix.X[mix.species_index('N2')]}")
print(f "O2 mole fraction: {mix.X[mix.species_index('O2')]}")

is the gri30 mechanism not suitable for such low temperatures?

thx a lot and greetings

joris

[Ray Speth]

Hi Joris,

Equilibrium and kinetics provide answers to different questions. Given infinite time, you should expect essentially all N2O to be converted back to N2 and O2. But that doesn't there is a reaction pathway that leads to that result in any reasonable time period -- the atmospheric lifetime of N2O is about 100 years. In fact, equilibrium calculations are done purely from thermodynamic properties of the species, and do not require defining any reactions.

Beyond that, I would exercise caution about using the GRI 3.0 mechanism for this kind of low-temperature chemistry. This mechanism was designed and validated only for combustion of natural gas. The decomposition of trace species like N2O at ambient temperatures is more in the realm of atmospheric chemistry, and I'd look in that literature for relevant reactions and rate parameterizations.

Regards,

Ray

[Joris Strassburg]

thx Ray!