Abstract
In recent years, the tomographic visualization of laminar and turbulent flames has received much attention due to the possibility of observing combustion processes on-line and with high temporal resolution. In most cases, either the spectrally non-resolved flame luminescence or the chemiluminescence of a single species is detected and used for the tomographic reconstruction. In this work, we present a novel 2D emission tomographic setup that allows for the simultaneous detection of multiple species (e.g., OH*, CH* and soot but not limited to these) using a single image intensified CCD camera. We demonstrate the simultaneous detection of OH* (310 nm), CH* (430 nm) and soot (750 nm) in laminar methane/air, as well as turbulent methane/air and ethylene/air diffusion flames. As expected, the reconstructed distributions of OH* and CH* in laminar and turbulent flames are highly correlated, which supports the feasibility of tomographic measurements on these kinds of flames and at timescales down to about 1 ms. In addition, the possibilities and limitations of the tomographic approach to distinguish between locally premixed, partially premixed and non-premixed conditions, based on evaluating the local intensity ratio of OH* and CH* is investigated. While the tomographic measurements allow a qualitative classification of the combustion conditions, a quantitative interpretation of instantaneous reconstructed intensities (single shot results) has a much greater uncertainty.
Highlights
Modern gas turbines are operated under lean fuel conditions to reduce NOx emissions, sometimes producing unstable operating conditions
We presented a novel 2D planar emission tomographic setup (POETλ ) for the simultaneous detection of multiple species using a single image intensified CCD camera
The alignment, spatial resolution and multispecies detection have been validated against premixed flat flames and laminar diffusion flames in which the distributions of OH*, CH* and soot are a priori known
Summary
Modern gas turbines are operated under lean fuel conditions to reduce NOx emissions, sometimes producing unstable operating conditions. Such instabilities are characterized by periodic fluctuations in the total volumetric heat release, which lead to considerable pressure fluctuations within the combustion chamber. In order to avoid these unstable operating conditions, an accessible measurement signal is required that correlates with the heat release rate of the flame. This signal can be used for online process control to avoid these unstable operating conditions, e.g., by varying the fuel supply
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