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The feasibility of using experimentally determined flow fields at intake valve closing, IVC, as initial conditions for computing the in-cylinder flow dynamics during the compression stroke is demonstrated by means of a computer simulation of the overall approach. A commercial CFD code, STAR-CD, was used for this purpose. The study involved two steps. First, in order to establish a basis for comparison, the in-cylinder flow field throughout the intake and compression strokes, from intake valve opening, IVO, to top dead center, TDC, was computed for a simple engine geometry. Second, experimental initial conditions were simulated by randomly selecting and perturbing a set of velocity vectors from the computed flow field at IVC.

A new methodology for rapidly characterizing the in-cylinder flow field at spark ignition for internal combustion engines is described in this paper. The process involves the use of 3-D particle tracking velocimetry to measure the flow field at intake valve closing (IVC) in a water analog engine simulation, and the use of CFD to compute the evolution of the measured flow field during the compression stroke, by using the experimental 3-D PTV results at IVC as the initial condition for the calculations. The technique has been applied to investigate the in-cylinder flow field of a typical 4 valve engine operating in two different modes; one or two intake ports active. The results indicate that in either mode the flow field at IVC is dominated by a different large scale structure: tumble in the case where both intake ports are active and swirl in the case where only one port is active. The results also indicate that these structures evolve differently during the compression stroke.

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.