Numerical and Experimental In-Cylinder Flow Study in a 4-Valve Spark Ignition Engine

Damian E. Ramajo, Norberto M. Nigro


Numerical and experimental techniques were applied in order to study the in-cylinder flow field in a commercial 4- valve spark ignition engine Fiat Torque. Investigation was focused in analyze the generation and evolution of tumble-vortex structures during the intake and compression strokes, and the capacity of this engine to promotes the turbulence enhancement during tumble-vortex degradation, at the end of the compression stroke. For these purposes, three different approaches were developed. Firstly, static flow bench tests were experimentally
carried out, and these were reproduced by computational fluid dynamics (CFD) simulations. Once the numerical techniques were assessed, a dynamic simulation of the full engine cycle
was performed for several engine speeds (1500 rpm, 3000 rpm and 4500 rpm) without consider the combustion (cold dynamic simulation). Static and dynamic cold-engine results were
compared in order to conclude about the significance of static-flow-test results to analyze the in-cylinder flow behavior.
Finally, combustion was taken into account and the full-cycle engine simulation (hot dynamic simulation) was developed for the same three engine speeds. Combustion phenomenon was introduced as an in-cylinder homogeneous heat source. For this, a simple predicting model was proposed in order to estimate the combustion rate as a function of the mean in-cylinder flow conditions (temperature, pressure, turbulent intensity and geometry of the combustion chamber). In addition, to getting more realistic results, 0/1-dimensional simulations were performed in order to feed appropriate boundary conditions for CFD simulations. All these results were employed to characterize the in-cylinder flow field of the engine, and at the same time, to conclude about the validity and usefulness of the different
engine tests (static flow tests, cold dynamic and hot dynamic simulation) to estimate the meanflow characteristics of the engine.

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