Friedrich-Alexander-Universität Erlangen-Nürnberg

Development of imaging measurement techniques for species and temperature mapping

Development of imaging measurement techniques for species and temperature mapping

Focus of this topic is the development of modern laser measurement techniques for investigation of combustion processes. For planar species and temperature mapping LIF (laser-induced fluorescence) based on a fluorescence tracer and LIP (laser-induced phosphorescence) based on phosphor particles are applied. For the optimization of those optical techniques special calibration setups like flow chambers are developed to increase accuracy and precision under high temperature-high pressure conditions relevant for IC engines and technical combustion systems. The techniques are applied for the characterization of mixture formation as well as for gas flow and surface thermometry. For engine applications with LIF a tracer (e.g. acetone, 3-pentanone) is added to the intake air of an optically accessible direct-injection spark-ignition engine (DISI) with exhaust gas recirculation (EGR) to simultaneously detect the residual gas and temperature field. The fluorescent marker is excited in the combustion chamber by two lasers of different wavelengths (“2-wavelength excitation-LIF”) to determine the local temperature. The temperature dependent fluorescence emission spectrum measured in a calibration cell is shown in the figure below. Temperature and species fields measured in an IC engine at elevated EGR fractions are shown in the right figure. Both images behave inversely, as the fresh air is cold and the exhaust gas in the cylinder is hot, i.e. in the range of low concentrations of fresh air there is a large proportion of exhaust gases at high temperature.

Fluorescence spectrum of acetone at 0.1 MPa with 308 nm excitation wavelength for different temperatures; normalized to uniform signal intensity, measurements are conducted in a calibration cell
Visualisation of temperature and air distribution with the tracer-LIF method in an optically accessible engine with EGR

For non-intrusive thermometry based on thermographic phosphors only one laser at 355 nm is utilized for phosphorescence excitation. Currently Dy:YAG phosphors (yttrium aluminium garnet doped with dysprosium) are utilized, as this phosphor is particularly interesting for its capability of standing extremely high temperatures. The spectral emission of the phosphorescence is temperature sensitive and can therefore be utilized for temperature calibration. For 2D gas temperature mapping the phosphor powder is seeded into the gas flow in a similar way like for particle image velocimetry (PIV). From two images of two cameras detecting different spectral regions an intensity ratio can be calculated to be applied for thermometry. For this measurement technique also calibration in an oven and special LIP-calibration setups is conducted to increase its accuracy for high temperature applications.

References:

Eichmann, S.C., Trost, J., Seeger, T., Zigan, L., Leipertz, A.: Application of linear Raman spectroscopy for the determination of acetone decomposition. Optics Express 19, No. 12, p. 11052-11058, 2011

Trost, J., Zigan, L., Eichmann, S.C., Seeger, T., Leipertz, A.: Characterization of acetone as tracer for laser-induced fluorescence under engine relevant conditions. Proceedings of the European Combustion Meeting, Cardiff, Wales, 2011

Trost, J., Löffler, M., Zigan, L, Leipertz, A.: Simultaneous Quantitative Acetone-PLIF Measurements for Determination of Temperature and Gas Composition Fields in an IC-Engine, Physics Procedia, 5, p. 689–696, 2010

Löffler, M., Beyrau, F., Leipertz, A.: Acetone laser-induced fluorescence behavior for the simultaneous quantification of temperature and residual gas distribution in fired spark-ignition engines, Applied Optics 49 (1) (2010) 37-49

Mission

SAOT provides an interdisciplinary research and education program of excellence within a broad international network of distinguished experts to promote innovation and leadership in the areas

Optical Metrology
Optical Material Processing
Optics in Medicine
Optics in Communication and Information Technology
Optical Materials and Systems
and Computational Optics.