Measurements of OH concentration in flames at high pressure by two-optical path laser-induced fluorescence

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Abstract
The two-optical path laser-induced fluorescence (TOPLIF) method was used to measure OH concentration profiles in flat, stoichiometric, premixed, methane–air flames burning at pressures ranging from 1 to 9 bars. The TOPLIF method does not require knowledge of the collisional quenching rates, which is a major advantage especially at these pressures. The population of a single rovibronic level is measured in a manner similar to many spectroscopic methods. TOPLIF measures this population at any location in flames at any pressure relative to this level’s population in an arbitrary reference flame (here the 1-bar flame at 5 mm above the burner). Absolute values can therefore be obtained from the known value in the reference flame. In addition, the TOPLIF method is proposed as a technique to process standard laser-saturated fluorescence measurements. Using our approach, we can properly correct variations in the effective probe volume with pressure.