Effects of Diluents on the Behavior of the Diluted Combustion Regime

The diluted combustion regime is studied with a non-premixed counter flow flame, in which methane and air are both preheated and diluted by N2 or N2/CO2. The flame stability diagram is presented for various diluents composition via changing the concentration of N2/CO2 ratio in diluents. Hydroxyl radical Planar Laser Induced Fluorescence (OH-PLIF) technique is used to analyze the effects of diluents, preheat temperature and fuel or oxygen concentration on the reaction zone characteristics, such as OH radical intensity distribution and reaction zone thickness, and an estimated flame temperature is introduced simultaneously. The results show that much CO2 in the diluents decrease the flame stability, especially for low oxygen concentration conditions, but preheating of reactants broadens the flammability domain. The preheat temperature shows more prominent effects on the flame thickness than reactant concentration under the flame condition examined. The addition of CO2 into the reactants lowers the OH intensity, flame temperature and the reaction zone thickness more efficiently than pure N2 dilution mainly because of its higher heat capacity