Staff

Motivation

To increase the efficiency of internal combustion engines, physical and chemical processes during operation need to be understood. Besides the flow field, the temperature and the species concentration in the gas phase, the investigation of near-wall phenomena are of main interest. To fully achieve knowledge of those heat transfer processes in internal combustion engines, surface temperatures have to be known. For this purpose, phosphor thermometry is applied to temporally and spatially resolve temperatures and temperature gradients on the inner surfaces of internal combustion engines.

Method and Theory

For thermometry purposes, a rare-earth or transition metal doped ceramic phosphor-material is coated on the object of interest and excited with an ultraviolet laser pulse. The emitted, time-resolved luminescence decay is a function of surface temperature and can therefore be employed for thermometry purposes. Based on a previously performed calibration the decay times can be converted into temperatures. The main advantages of this technique are its robustness against soot radiation and chemiluminescence, which both occur in internal combustion engines. Furthermore, it offers high spatial and temporal resolution over a broad range of temperatures. Point wise measurements can be performed using a photomultiplier as a detector, while CMOS high-speed cameras allow two-dimensional surface temperature measurements.

Proceeding

As a first step, an appropriate phosphor material has to be identified and characterized, which fits well in the temperature and time-scales prescribed by the engine. Using this thermographic phosphor, temperature measurements of selected parts of an optically accessible internal combustion engine are to be performed two-dimensionally. Furthermore, an endoscopic approach is planned, to measure surface temperatures inside a thermodynamic internal combustion engine under more realistic conditions.

Publications

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