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Internal Combustion Engines Fundamentals Episode 2 part 10

Tham khảo tài liệu 'internal combustion engines fundamentals episode 2 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 810 INTERNAL COMBUSTION ENGINE FUNDAMENTALS symmetry plane are not predicted. The approximate magnitude of the turbulence intensity levels are predicted but the values within the conical intake jet are underestimated. Figure 14-32 shows in-cylinder swirl velocity predictions and measurements in an engine with a disc-shaped chamber and helical intake port during the intake and compression strokes. Again the major features of the experimental profiles are predicted adequately though differences in detail are significant.59 Comparative multidimensional modeling studies of different turbulence models 63 differencing schemes 59 65 and number of grid points59 indicate the following. Differences in the form and coefficients of the dilation term in the k-e turbulence model have only modest effects on flow field predictions. Higher-order turbulence models might provide improved accuracy.65 Both mesh refinement more finely spaced grid points and use of higher-order differencing schemes have been shown to improve significantly the accuracy of the predictions often of course with substantial increases in computing requirements.59 Examples of predictions of other types of engine flow processes are the following. Squish flows into bowl-in-piston combustion chambers have been extensively analyzed. Figure 14-33a shows the flow field into and within an off-axis bowl in piston at 20 BTC of the compression stroke. The strong radially inward squish flow at the bowl lip is apparent. However the bowl-axis offset produces a stronger flow where the squish region is greatest in extent and results in a net flow across the bowl center plane and a complex flow pattern within the bowl. Turbulence intensity results are often displayed on contour plots. Figure 14-33Ử shows the turbulence intensity distribution within the bowl at TC after compression. The correspondence between high-velocity regions generated by the squish flow Fig. 14-33a and higher turbulence intensities is apparent. A .