The Effect of In-Cylinder Flow Processes (Swirl, Squish and Turbulence Intensity) on Engine Efficiency — Model Predictions

Abstract

<div class="htmlview paragraph">A computer simulation for the performance of a four-stroke spark-ignition engine is used to assess the effects of in-cylinder flow processes on engine efficiency. The engine simulation model is a thermodynamic model coupled to submodels for the various physical processes of in-cylinder swirl, squish and turbulent velocities, heat transfer and flame propagation.</div> <div class="htmlview paragraph">The swirl and turbulence models are based on an integral formulation of the angular momentum equation and a K-ε turbulence model, These models account for the effects of changes in geometry of the intake system and the chamber design on in-cylinder flow processes. The combustion model is an entrainment burn-up model applicable to the mixing controlled region of turbulent flame propagation. The flame is assumed to propagate spherically from one or two spark plug locations. A heat transfer model that is dependent upon the turbulence level is used to compute the heat loss from the unburned and burned gases. These submodels are calibrated from experimental data.</div> <div class="htmlview paragraph">In this paper a combustion system featuring high and low swirl generating ports, a flat head and various piston designs is investigated. A parameter study is conducted to determine the effects of in-cylinder geometry on burn duration, heat transfer and fuel consumption. These results indicate that swirl, squish and turbulence intensity levels can be varied to produce a minimum in fuel consumption for the conditions examined. In addition, the isolated effect of the turbulence intensity on engine efficiency is presented for various EGR levels.</div>