Experimental and kinetic modeling study of the oxy-fuel oxidation of natural gas, CH4 and C2H6

• The oxy-fuel oxidation of methane, ethane and natural gas is evaluated experimentally.
• The chemical kinetic model is able to reproduce adequately the experimental trends.
• CO2 is able to react with CH2 while reactions with C2 radicals are negligible.
• The effect of CO2 as collision partner in sensitive third-body reactions is minor.
• Reaction paths are similar to air combustion except for CO2 reaction with H and CH2.

The oxidation of simulated natural gas mixtures, methane and ethane under oxy-fuel conditions has been studied experimentally in a flow reactor, at atmospheric pressure and in the 773–1673 K temperature range. The influence of the stoichiometry has been analyzed by varying the excess air coefficient (λ) from fuel-rich (λ = 0.2) to fuel-lean (λ = 2) conditions.The results are interpreted in terms of a chemical kinetic model for the oxidation of small hydrocarbons. The updated kinetic mechanism in relation to the CH4 and C2H6 subsets, together with the interactions between CO2 and C1–C2 hydrocarbon radicals, is able to reproduce satisfactorily the experimental trends. Concerning C1 radicals, only CH2 is able to consume significant quantities of CO2, whereas the reactions with C2 radicals are insignificant under the present conditions.The effect of CO2 as collision partner on important third-body reactions is evaluated and the major pathways of the oxidation of natural gas, methane and ethane are identified. The reaction paths for all fuels tested are found to be similar to those in air combustion, except for the interactions of CO2 with H and CH2 radicals and the lower importance of reactions between H radicals and hydrocarbons in oxy-fuel combustion.