Development and application of simultaneous 2D flow velocity and gas temperature measurements using thermographic phosphors under engine-relevant conditions
A non-intrusive laser diagnostics technique has been developed for simultaneous meas-urements of velocity and gas temperature in optically accessible internal combustion engines. The technique, thermographic PIV (T PIV) combines phosphor thermometry and particle image velocimetry (PIV) and offers the possibility of simultaneous meas-urement of gas temperature and velocity. Suitable phosphor materials were selected by testing three commercially available phosphors: BAM:Eu2+, ZnO and ZnO:Zn. The lumi¬nescence emission and the spectral response to various parameters including temperature were measured yielding a tem-perature-dependent calibration curve to be used for signal interpretation in engine ex-periments. The ZnO:Zn phosphor shows the highest sensitivity to temperature allowing higher temperature precision. Therefore, ZnO:Zn phosphor was chosen as the suitable candidate for engine measurements. Measurements were performed in an internal combustion engine at a speed of 1200 rpm with a sampling rate of 10 Hz between 180 and 540°CA under motored conditions. The temperature and velocity fields were meas-ured successfully at various times through-out the compression and the exhaust stroke. The obtained temperature fields are com-pared with simulated bulk-gas temperatures from a 0D model-based simulation showing a temperature deviation of around 1% (200°CA) to 14% (480°CA) from the model. The measurement accuracy was found to be 55 K (18%) at 300 K and 2 K (0.3%) at 614 K for the 200-cycles average. The potential of the diagnostics was tested also in in cylinder post-combustion gases. In this case, the diagnostics was failing proba-bly due to the characteristics of the phos-phor used, which does not seem to resist to high combustion temperatures degrading its luminescence properties. The potential of T-PIV in post-combustion gases remains under the conditions of finding more resistant phosphor particles.
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