An Investigation of Fluid Flow During Induction Stroke of a Water Analog Model of an IC Engine Employing LIPA 950726
This paper presents results from experiments performed in an axisymmetric water analog model of a four-stroke IC engine using the optical velocimetry technique LIPA (Laser Induced Photochemical Anemometry). The investigation can be described as a fundamental scientific inquiry into the fluid dynamics encountered during engine operation, with the long term goal of increasing performance. An application of LIPA to a fluid dynamics problem delivers two-dimensional fields of velocity vectors which are projections of the full three-dimensional vectors in single measurement steps. From an evaluation of a velocity field vorticity information can be obtained readily. Velocity fields and vorticity distributions are, in this study, the basis for the evaluation of seven parametric quantities. Some of these may become tools that give engineers ‘rule of thumb’ indications of the mixing that is occurring. Fields of velocity vectors and vorticity distributions, along with the seven parametric quantities serve to characterize the fluid dynamics inherent in the flow fields.
The flow field during the intake stroke of the four-stroke model was investigated by varying two engine parameters, engine speed and valve lift (the valve lifts chosen were fixed during the intake stroke). The range of engine speeds investigated are below or near low idling conditions. Clear tendencies could be observed for the kinetic, fluctuation, and vortical energies contained in fluid flow in an area that is governed by a recirculation pattern that scales with engine volume. These energies increase with increasing engine speed and decreasing valve lift. For that same region it was found furthermore that the length scales of the existing flow structures are -- for the range of length scales studied -- independent of the setting of the engine parameters, and that the rotational strength in connection with these scales increases with increasing engine speed and decreasing valve lift. Another result outlined in this paper is an assertion of the significance of the fluid dynamics of azimuthal vortex rings, that are created in the shear layer of the annulus jet, with respect to the physics of fluid flow in an engine.