PLIF Thermometry Based on Measurements of Absolute Concentrations of the OH Radical

Abstract

Laser-induced Fluorescence / Thermometry / Lean Combustion / Gas Turbine A method for measurements of planar temperature distributions based on planar laser-induced fluorescence (PLIF) of the OH radiacal is described. The technique was developed specifically for the application in lean combustion systems, where OH equilibrium concentrations are largely independent on equivalence ratio and a function of temperature only. It is thus possible to derive a temperature information from measurements of absolute OH concentration, which can be obtained from a combined PLIF/absorption measurement. This paper discusses the basics of the method, and describes validation experiments in high pressure laminar premixed flames which were performed to asses its applicability and accuracy. Therefore, we compared our LIF based results with CARS measurements performed in the same flames. Finally, an example for the application in a lean gas turbine model combustor is discussed.

Experimental Investigation of Flame Stabilization in a Turbulent Premixed Recirculation-Stabilized Jet-Flame with Simultaneous kHz Laser Diagnostics

“…13,14 Moreover, the OH-LIF intensity can be seen as a qualitative temperature information of the burned gas. 15 For the OH-LIF measurements, a highspeed dye laser (Sirah Credo Dye) tuned to a wavelength of 283.305 nm was used to excite the Q 1 (7) transition within the 0 → 1 vibrational band of the OH A 2 Σ + − X 2 Π band system. It was operated at the same repetition rate of 5 kHz as the PIV and the OH*-CL setup, and the LIF laser pulse was placed in between the two PIV pulses, to get a truly simultaneous measurement.…”

Time-resolved temperature profile measurements in the exhaust of a single sector gas turbine combustor at realistic operating conditions

“…Under the given boundary conditions (i.e. elevated pressure, high preheating temperatures), the chemical relaxation time of the OH super-equilibrium concentration of < 0.1 ms (Heinze et al 2011) is substantially shorter than the OH transit time of 4 − 7 ms (see Sect. 3.5) between the primary zone and the measurement location at the combustor exit.…”

“…The underlying concept of the in-situ high-speed temperature measurement technique used in this experiment is to determine optically the absolute local concentration of the OH radical as a highly sensitive temperature indicator molecule, whose concentration grows nearly exponentially with respect to temperature (Heinze et al 2011;Morley 2005). The applicability of this method is restricted to areas with a lean mixture ( ≥ 1.1 or ≤ 0.9 ) and chemical equilibrium (Heinze et al 2011). Under these conditions, the OH concentration is approximately independent of the equivalence ratio and can be assigned unambiguously to temperature.…”

The Role of CFD in Modern Jet Engine Combustor Design

“…When it comes to compare fields like temperature, the difficulties in having reliable measurements in the flame region lead, in the few cases where measurements are available at high pressure conditions, to significant uncertainties and this slows down the validation process of CFD models. For the studied configuration, direct measurements of OH concentration are available, with an uncertainty of 20-30% [73]. As other intermediate species, OH can be used to have a qualitative picture of the flame configuration and thus this quantity is still valuable for CFD validation purposes.…”

“…Unfortunately, direct measurements of temperature at high pressure condition are challenging as explained earlier and this quantity is if often estimated indirectly by making additional assumptions, which in turns lead to additional uncertainty. For example, for the combustor test case investigated here temperature can be estimated from OH concentration via equilibrium assumption [73]. A direct comparison of the experimental temperature in this case with that obtained in the LES from Eq.…”