Development of laser-induced phosphorescence technique for visualisation of temperature and flow fields in IC engines

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Aim of the project is the development of the two-colour laser induced phosphorescence technique for simultaneous visualisation of gas temperature and velocity fields under IC engine conditions. The technique will be utilized for imaging of mixture formation, ignition and combustion. Furthermore, this measurement technique can be utilized for fundamental studies and for optimization of many systems related to energy technology and chemical process technology. Inert YAG:Dy particles with a temperature-dependent luminescence signal are utilized, which can be additionally used for velocity determination. In the first phase of the project the signal intensity of the phosphor particles was significantly enhanced by doping additional sensitizers like Erbium (Er) und Praseodymium (Pr) to the phosphors.These optimized phosphors YAG:Dy:Er and YAG:Dy:Pr are applicable for high temperature measurements above 1000 K and will be utilized for the planned studies under IC engine conditions. However, further modifications and variations of the host material are necessary in order to increase signal intensity and thus, measurement accuracy at high temperatures while decreasing the luminescence duration. In the first phase of the project a flow cell was set up and a characterization and calibration of the phosphorescence was conducted e.g. depending on temperature, pressure and surrounding gas phase up to 720 K. For a calibration at temperatures higher than 1000 K, a new calibration system is necessary. The design of the high temperature calibration cell and the high temperature calibration is the second main goal of the project. The new cell is based on a porous media burner enabling a wide temperature range for the planned calibration measurements. After successful optimization and calibration, the measurement technique will be applied under IC engine conditions, which is the third main goal of the project. The possibility of the simultaneous measurement of temperature and velocity fields will be applied for the study of mixture formation and ignition processes. For this purpose, a rapid compression machine (RCM) with a spark ignition system is available. Measurements during the compression stroke for resolving temperature inhomogeneities and turbulent flows during mixture formation are conducted as well as auto-ignition processes will be studied occurring around top dead centre. Auto-ignition is initialized in hot regions in which a reactive mixture is present and where the turbulence is not too high. Furthermore, under spark-ignition IC engine conditions with late injection timing, the region at the spark plug will be studied in detail regarding temperature and velocity fields. The local vaporization cooling and the resulting temperature stratification will be resolved as well as the spray-induced turbulent flow. Thus, the cyclic variation and its influence on ignitability will be identified.