F2010B071
Fuel Spray Parameter Analysis for Different Common-rail Injectors
The paper presents the results of a comparative analysis of the changes in the injection spray shape, penetration and its vertex angle during the injection through piezoelectric and electromagnetic fuel injectors. The results of the observation of the fuel spray with the use of high speed camera (100 us frame frequency) have been presented. The parameterization and digital processing (including its automation) of the obtained image have too been presented. The influence of the pressure and timing of the injection on the variable-in-time spray parameters have been shown. A mathematical model describing these relations has been proposed. Electromagnetic injectors were used in the first and second generation common rail (CR) systems. The reason for their withdrawal in favor of the piezoelectric injectors is the lack of the possibility of obtaining small time intervals between the subsequent fuel doses in a single engine operating cycle. Hence, the number of injections was limited to three or four in a single cycle. Piezoelectric injectors are fitted in third generation CR systems. Their main advantage is the possibility of a multiple division of the fuel dose into doses of relatively short durations. The issue discussed in this paper consisted in the application of optical observation and digital analysis of the obtained images of the fuel spray development in order to determine the comparative fuel spray indexes and, on this basis, providing and objective assessment of the fuel injection and the spraying processes. A particularly significant issue was to explain how the basic injection parameters (injection pressure, duration of the injection, hole diameter) influence the change in the selected indexes that are possible to determine for the injected fuel spray. The authors also tried to collect proper research material that would be used to determine the functional relations between these parameters and the values of the comparative indexes. Such a relation - expressed in a form of model dependencies - could be used to predict a shape, vertex angle and the speed of the spray front for the assumed values of these parameters. Based on the conducted investigations it has been observed that, the here presented Hiroyasu and Dent models are fit for larger diameters of the injector holes (above 0,2 mm in diameter); this is also confirmed in other investigations. As far as the fuel spray penetration is concerned the models show smaller penetration values than it results from the experiments.
This abstract is supplemented by a PDF, which can be viewed here.
Poster presentation: Vehicle design and development