Effects of addition of electrolysis products in methane-air diffusion flames

摘要

Evaluation of steam-added methane-hydrogen blends through the comparison of flame structures and pollutant emissions is numerically conducted with detailed chemistry. The composition of fuel is systematically changed from pure methane and pure hydrogen to the blending fuel of methane-hydrogen-steam through the molar addition of H_2O. Flame structure is changed considerably for CH_4-H_2 flames and CH_4-H_2-H_2O flames in comparison to pure methane flame. The discernible differences in major flame structure are compared among a pure methane flame, CH_4-H_2 flames and CH_4-H_2-H_2O flames. Especially, emission indices of CO increase and then decrease after showing a maximum in the increase of methane mole fraction for CH_4-H_2 flames and in the increase of H_2O mole fraction for CH_4-H_2-H_2O flames, while those of CO_2 increase monotonously. These behaviors are mainly caused by the competition of the production through the reaction step HCO + H_2O → H + CO + H_2O with the destruction of CO by the reaction step CO + OH → CO_2 + H. The changes of thermal NO and Fenimore NO are also analyzed for various combinations of the fuel composition. Importantly, contributing reaction steps to thermal NO and Fenimore NO are addressed in pure methane, CH_4-H_2 flames and CH_4-H_2-H_2O flames.