Measurement of Cycle-to-Cycle Variations and Cycle-Resolved Turbulence in an IC Engine Using a 3-D Particle Tracking Velocimetry

Measurements of the instantaneous in-cylinder flow fields were carried out in a water analog engine simulation rig using a state of the art 3-D Particle Tracking Velocimetry(3-D PTV).Raw images for the 3-D PTV measurements were acquired at the end of intake stroke (Bottom Dead Center, BDC) for a simulated idle condition using a pair of high speed video cameras. Efforts were made to maximize the particle seeding density(and the resulting number of 3-D velocity vectors)to yield approximately 500 to 600 instantaneous vectors at each cycle. Using an appropriately designed spatial filter, large scale(low pass filtered) 3-D instantaneous velocity fields were reconstucted for each cycle as well as the ensemble averaged flow fields over large number of cycles. Based on these cycle-resolved(low pass filtered)flow fields and the ensemble averaged flow field, cycle-to-cycle variations were computed. Furthermore, the deviations of the instantaneous flow fields from the corresponding cycle-resolved large scale motions were computed to estimate the root mean square(rms)levels of the "in-cycle"turbulence. This paper presents the unique application of the 3-D PTV and the water analog engine simulation approach not only to measure the ensemble averaged mean 3-D flow patterns, but also to study the cycle-to-cycle stability of such flow patterns and ultimately to gain a better understanding of the combustion stability characteristics.