Modeling ion and electron profiles in methane-oxygen counterflow diffusion flames

Charged species formed in a laminar counterflow diffusion flame of methane and oxygen enriched air are studied numerically. Mole fractions of major individual charged species are predicted using a one-dimensional counterflow diffusion flame model. The Cantera software and the laminar counterflow flame model is used to solve one-dimensional conservation equations of reactive flows to obtain the spatial profiles of velocity, the mole fractions and the temperature in the steady state. The distance between the two nozzles is kept at 2 cm. A detailed transport model and a 65 step mechanism involving 11 charged species in addition to the 208 step methane-air combustion mechanism with neutral species is used to model the electrical properties of the flame. Strain rate is changed from 10^s-1 to 90^s-1 in steps of 10^s-1 by adjusting the mass fluxes of the fuel and oxidizer. The oxygen content in the oxidizer is varied from 21% to 100%. The effects of strain rate and oxygen content variation on the charged species profiles are comparatively analyzed. Electrons and H₃O⁺ appear to be the most dominant negative and positive charged particles respectively. OH^-is found to be the most dominant species amongst the negative ions. The increase in oxygen content from 21% to100% causes approximately twofold increase in both the electron and H3O+ concentrations. The maximum concentration of electrons increases from 1.4?10¹¹ cm^-3 to 2.8?10¹¹ cm^-3 by increasing oxygen content in the oxidizer from 21% to 100% respectively. Also the maximum concentration of H₃O⁺ increases from 1.8?1010 cm^-3 to 2.4?10¹⁰ cm^-3 by increasing oxygen content in the oxidizer from 21% to 100% respectively. The maximum concentration of OH^-increases from 10⁹ cm^-3 to 7?10⁹ cm^-3. The total negative charged species excluding the electrons as well the total positive ions are computed and it is shown that the amount of negative ions is negligible as compared to the positive ions and the electrons are the most dominating negatively charged particles. The computational results obtained through this solution need to be verified with experimental data.