Endoscopic temperature imaging in a four-cylinder IC engine via two-color toluene fluorescence

Building on the development of a large-aperture, UV-transparent endoscope designed specifically for use in IC engines, the gas-phase temperature in a fired, multi-cylinder engine was imaged based on laser-induced fluorescence (LIF) of a fuel tracer. Laser light at 266nm was formed into a light sheet...

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Bibliographic Details
Published in:Proceedings of the Combustion Institute 2015-01, Vol.35 (3), p.3697-3705
Main Authors: Gessenhardt, C., Schulz, C., Kaiser, S.A.
Format: Article
Language:English
Subjects:
Combustion
Computer simulation
Endoscopes
Engines
Fluorescence
Fuels
Imaging
Mathematical models
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Summary:Building on the development of a large-aperture, UV-transparent endoscope designed specifically for use in IC engines, the gas-phase temperature in a fired, multi-cylinder engine was imaged based on laser-induced fluorescence (LIF) of a fuel tracer. Laser light at 266nm was formed into a light sheet via a laser-input endoscope and excited fluorescence of toluene, port-fuel injected in a mixture with the base fuel iso-octane. The resulting UV-LIF signal was collected by an endoscope head in the combustion chamber, split into two wavelength-channels by a dichroic beam splitter, and detected on two separate cameras. Exploiting the temperature-dependence of the LIF spectrum, quantitative images of temperature were derived from the pixel-wise ratio between the two images. We describe the procedures for cross-registration of the two images and calibration of the LIF-temperature conversion, which are more challenging compared to fully optically-accessible engines. To assess the systematic error we performed a quasi-dimensional simulation matched in detail to engine data. Between intake-valve closure and mid-compression, the temperatures derived from the model and that from LIF agreed within 5K, while the difference increased to 50K at 28CA before compression top-dead center. In addition to such quantitative imaging in the compression stroke, unburnt fuel was detected in the residual gas. This feature unexpectedly enabled qualitative imaging even after combustion. Predicted by the simulation, the initial back-flow of exhaust gas into the intake during gas exchange could be visualized on a single-shot basis.
ISSN:1540-7489
DOI:10.1016/j.proci.2014.06.085