Experimental study on the diluted combustion mechanism using hydroxy radical planar laser induced fluorescence method

In order to investigate the effects of preheat temperature and dilution rate of reactants on the dilution combustion mechanism, a laboratory-scale nitrogen diluted methane/air counter flow non-premixed flamed was studied using hydroxy radical planar laser induced fluorescence (OH-PLIF) method. Taking the reaction zone thickness of OH radical as flame thickness, it shows that flame thickness decreases with the increase of dilution rate at constant preheat temperature and increases with preheat temperature at fix dilution rate under the conditions examined in this experiment in which preheat temperature is not very high. However, further analysis of experiment results shows that flame thickness increases with the increase of dilution rate when the reactants are highly preheated. Moreover, according to the flame thickness variation condition and the collaboration of increasing effects of preheat temperature and decreasing effects of dilution rate on the chemical reaction rate, preheat temperature is regarded as the dominant factor under low preheated reactants diluted combustion condition but dilution rate is regarded as the dominant factor under highly preheated reactants diluted combustion in which dilution decrease the reaction rate and leads to the increase of flame thickness or flame volume.