Effects of Poerating Speed on 3-D Mean Flows Measured at the End of Intake Stroke in an IC Engine

Abstract

Measurements of the instantaneous in-cylinder flow fields at the end intake stroke at bottom dead center(BDC)were carried out in an FloDyne^TM water analog engine simulation rig using 3-D particle tracking velocimetry(3-D PTV). The measurements were performed in a 4-valve per cylinder, typical pent-roof type combustion chamber with both intake valves activated generating mainly tumble vortex structures. The experiments were repeated for two different operating points simulating an idle condition(600 PRM)and a low load condition(1200 RPM). These two operating points represent almost a factor of two in effective Reynolds(Re)numbers. For each case, 100 cycles of data were acquired. Efforts were made to optimize the particle seeding density(and the resulting number of 3-D velocity vectors)to yield 500 to 600 instantaneous vectors at each cycle. The raw data coosisted of sets(between 50 000 and 60 000 velocity vectors each)of 3-D instantaneous(but phase conditioned at BDC)velocity vectors, randomly(but relatively uniformly)distributed over the entire cylinder volume. Sophisticated statistical tools were applied to these data sets to evaluate the ensemble averaged mean flow field and total fluctuation fields in the root mean square(r.m.s.)sense. In addition, "conventional" integral measures such as tumble, cross-tumble and swirl ratios were computed from the data by integrating the angular momentum components over the cylinder volume. The results indicate that the Re number effects are relatively small between the two conditions investigated, with a tendency of the smaller scale structures at BDC for the higher Re number case. This paper illustrates the tremendous potential of the water analog engine simulation used in conjunction with 3-D PTV as a rapid engine flow field evaluation tool. This approach allows to conveniently obtain 3-D maps of the mean and total r.m.s.fluctuation levels of each velocity components as well as integral parameters such as tumble and ratios(under realistic unsteady conditions). Furthermore, this method also allows various configurations or operating points to be conveniently compared with respect to many of their flow characteristics.