The Application Of The PLIF Technique To The Measurement Of In-cylinder Mixture Temperature And Concentration In An Engine

Homogeneous charge compression ignition (HCCI) is an effective way toimprove the efficiency of gasoline engine. The autoignition timing of a HCCI engineis influenced by the in-cylinder mixture temperature and concentration. Therefore, themeasurement of in-cylinder mixture temperature and concentration distribution hasgreat significance for revealing HCCI combustion characteristics. Based on the planarlaser induced fluorescence, in-cylinder mixture temperature and concentrationdistributions were quantitatively analyzed. This thesis includes the following:One calibration measurement system was established in order to produce twofluorescence spectrums with different wavelengths after induced dual tracers with onelaser. Fluorescence images were taken at different mixture temperature, pressure andconcentration in the system. Based on the MATLAB software, a code was written toanalyze the images under the conditions of calibration and engine operation. Therelations among fluorescence intensity of different tracers, fluorescence ratio andmixture temperature, pressure, concentration were obtained. Moreover, experimentswere carried out on one single cylinder optical engine, in-cylinder mixturetemperature and concentration distribution characteristic at different crank angleswere analyzed. The research results show that:The fluorescence intensity and fluorescence ratio (Triethylamine/3-pentanone)were influenced by ambient pressure, temperature and mixture concentration. Thefluorescence intensity of3-pentanone increases with pressure, while it decreases withtemperature. However, the fluorescence intensity emitted from TEA (Triethylamine)show a different change trend with ambient pressure relative to3-pentanone. As themixture gets richer, the fluorescence intensity becomes stronger. The fluorescenceratio of TEA and3-pentanone increase when ambient temperature rises and isproportion to the mixture concentration. As the piston moves towards the top deadcenter (TDC) in the compression strokes, the mixture temperature in the cylindergradually rises, and the higher temperature region is around the center of the cylinder,and gradually expands. But there is obvious thermal stratification in the cylinder. Inthe NVO (negative valve overlap) period, the in-cylinder mixture temperaturedistribution is inhomogeneous, but the high temperature region is still around thecylinder center. After the recompression and the reexpansion, the mixture temperaturein the cylinder become more uniform compared to the case at the initial stage of NVO.In the compression stroke, the mixture gradually becomes homogeneous as the pistonapproaches the TDC, but there is slightly rich mixture in the intake side.