Control of emissions by gaseous additives in methane–air and carbon monoxide–air flames

Control of emissions such as nitrogen oxides and carbon monoxide, was analytically investigated by using hydrogen and carbon monoxide as an additive to methane–air flames and using methane as an additive to carbon-monoxide–air flames. The effect of these additives on the burning velocity was also investigated. These flames were simulated by one-dimensional model incorporated detailed representation of transport fluxes and chemical kinetic mechanism which involves CH4–H2–CO–NOx chemistry. The mechanism consists of 59 reactions among 25 chemical species. The predicted burning velocities from the model were found to be in close agreement with the corresponding experimental data and this validate the kinetic model. The burning velocities with H2 and CO additive for CH4–air flames are correlated linearly. Results indicate that, the addition of small amounts of H2 to CH4–air flames decreases the NOx (in lean and rich flames) and CO (in rich flames) while increasing significantly the burning velocity. This is due to the change of the radical concentrations. Also, the addition of CO to CH4–air flame increase the mole fraction of NOx, CO and burning velocity at most of the conditions. The addition of CH4 to CO–air flames leads to increase the burning velocity, while NOx and CO species increases until they reach their peaks at certain concentrations and then decrease again.