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Accurate prediction of engine combustion characteristics, especially burn rates, can eliminate a number of hardware iterations, thus resulting in a significant reduction in design and developmental time and cost. An analytical methodology has been developed which allows the determination of part-load MBT spark timing to within 2 crank-angle degrees. The design methodology employs the in-house-developed steady-state quasi-dimensional engine simulation model (GESIM), coupled with full-field measurement of the in-cylinder fluid motion at bottom dead center (BDC) in the computer-controlled water analog system (AquaDyne). The in-cylinder flow-field measurements are obtained using 3-D Particle Tracking Velocimetry (3-D PTV), also developed in-house. In this methodology, the in-cylinder flow measurement data are used to calibrate both the tumble and swirl models in GESIM.

Flow fields generated during the intake stroke of a 4-stroke I.C. engine are studied experimentally using water analog simulation. The fluid is seeded by small flow tracer particles and imaged by two digital cameras at BDC. Using a 3-D Particle Tracking Velocimetry technique recently developed, the 3-D motion of these flow tracers is determined in a completely automated way using sophisticated image processing and PTV algorithms. The resulting 3-D velocity fields are ensemble averaged over a large number of successive cycles to determine the mean characteristics of the flow field as well as to estimate the turbulent fluctuations. This novel technique was applied to three different cylinder head configurations. Each configuration was run for conditions simulating idle operation two different ways: first with both inlet ports open and second with only the primary port open.

Measurements of the instantaneous in-cylinder flow fields were carried out in a water analog engine simulation rig using 3-D Particle Tracking Velocimetry[1]. Two different configurations based on a 4-valve per cylinder engine with a typical pent-roof type combustion chamber were investigated. Measurements were performed at the end of intake stroke at BDC for simulated idle conditions. Efforts were made to maximize the particle seeding density (and the resulting number of 3-D velocity vectors) to yield 250 to 300 instantaneous vectors at each cycle. Using an appropriately designed spatial filter the low pass filtered (large scale) instantaneous velocity fields were reconstructed for each cycle. The spatial cut-off of the filter was set to 1/3 of the engine bore diameter. Based on these cycle-resolved flow fields, the cycle-to-cycle variations as well as the cycle resolved turbulence fluctuations were computed.