Experimental investigation of methane/(Ar, N ₂, CO ₂)-air mixture combustion in a two-layer packed bed burner

The flame stability, radiation output, and emissions of methane/(Ar, N ₂, CO ₂)-air mixture combustion in a two-layer porous burner packed with alumina spheres were studied. Independent variations in the flame temperature were achieved by substituting CO ₂ in the fuel with an equal amount of N ₂ or Ar. The inert gas diluted percentage ranged from 25% to 40% at equivalent ratios within 0.75-0.95. The flame stability limits and temperatures were found to be influenced by thermal properties and inert gas addition. The upper and lower stability limits of the CO ₂-diluted flame were relatively lower than those of the N ₂- and Ar-diluted flames because of the larger heat capacity of CO ₂ and its dissociation. The flame temperature and speed decreased with the increased inert gas percentage in the fuel. The Ar-diluted fuel had higher flame temperatures and pressure drops than the CO ₂- and N ₂-diluted fuels. The NO _x emissions were influenced by both the species of inert gas and its additive mole fraction. However, CO and hydrocarbon emissions were mainly affected by the inert gas diluted concentration.