Aim
For studying gaseous flows, fuel distributions or mixing processes, often a mixture of fluorescence tracers in a non-fluorescing environment is used to visualize the gas flow, e.g., via laser induced fluorescence (LIF). Most tracers show significant dependences of their fluorescence yield on pressure, temperature and gas composition. For an exact analysis of LIF measurements these fluorescence properties of the tracers for defined conditions need to be known. The data gained in the high pressure cell are used on the one hand, for the empirical analysis of measurements and, on the other hand, for developing and refining fluorescence models for predicting fluorescence yields under certain conditions. In this case not only the spectral profile and the intensity of the fluorescence signal is of interest, but also the effective fluorescence lifetime yields important information. Therefore, in our work the measurement of fluorescence lifetimes is of great interest.

Approach
The cell is constructed as a flow cell. It is designed for a pressure range up to 10 bar and a temperature range from room temperature to 1000°C. The cell is internally heated by MoSi heating elements. The gas flow is directed through a ceramic tube system for heating up the flow and then led through the measurement volume. The gas flow is seeded with the respective tracer by an evaporation system. A second gas flow and a gas mixing chamber allow different gas compositions to be realized. A frequency-quadrupled Nd:YAG laser with a pulse length of 30 ps is served as excitation source. This enables fluorescence life times down to about 100 ps to be measured. Three different detection systems are available: A standard ICCD camera with spectrograph (for spectrally resolved measurements), several photomultipliers (for lifetime measurements) and a streak camera with spectrograph.

References
W. Koban, J. D. Koch, R. K. Hanson, and C. Schulz "Toluene LIF at elevated temperatures: Implications for fuel/air ratio measurements," Appl. Phys. B 80, 147-150 (2005).

Contact
Dr. T. Endres, Torsten Endres, Tel  +49 (0)203 - 379 3505, IVG