Simultaneous absorption and PLIF measurements of OH and kerosene for reliable single-pulse temperature and fuel measurements in lean jet engine combustors

Abstract

The development of modern low pollution jet engines requires data on fuel and temperature distributions under varying operation conditions. In addition, lean premixed combustion is potentially prone to combustion instabilities, therefore time resolved measurement techniques are highly desirable. By combining planar laser induced fluorescence (PLIF) and absorption measurement techniques, a new sensitive planar laser measurement technique, which is reliable and efficient under realistic test conditions will be presented for time resolved determination of flame temperature and fuel distribution in lean pressurized combustion systems. PLIF of the OH radical as temperature indicator and kerosene PLIF to determine fuel distribution is used to characterise the flame. In technical combustion systems the PLIF measurement leads generally to the problem of laser absorption and of the interference of OH and kerosene LIF. The simultaneous detection of the PLIF signal by two cameras using different spectral filters reduces the interference difficulties substantially. A simultaneous measurement of laser absorption and OH LIF leads to an absorption correction and to the absolute calibration of the OH image. The temperature can be deduced from the OH equilibrium concentration, which grows exponentially with temperature, in lean flames (phi<0.9) nearly independently of phi. The high temperature sensitivity of this method, which is about 8 times higher than the sensitivity of the usually used OH 2-line thermometry, enables the reliable statistical evaluation of the single-pulse temperature images.