The optimization of the vaporization and mixture formation process is of great importance for the development of modern gasoline direct injection (GDI) engines, because it influences the subsequent processes of the ignition, combustion and pollutant formation significantly. In consequence, the subject of this work was the development of a measurement technique based on the laser induced exciplex fluorescence (LIF), which allows the two dimensional visualization and quantification of the in-cylinder air/fuel ratio.
A tracer concept consisting of benzene and triethylamine dissolved in a non-fluorescent base fuel has been used. The calibration of the equivalence ratio proportional LIF-signal was performed directly inside the engine, at a well known mixture composition, immediately before the direct injection measurements were started. Thus, it was possible to minimize crucial effects caused by window fouling, the non-uniformity of the laser illumination and finally the optical particularities of the setup.
For comparison with the LIF results, Raman measurements were carried out simultaneously. In addition to different engine operating points in the homogeneous regime, the mixture formation was also investigated at stratified charge. A comparison between the results of both measurement techniques shows very good agreement for cycle resolved measurements as well as for the mean values of the air/fuel ratios.