CFD Analysis of Intake-System Performances of a Small Turbocharged Spark-Ignition Engine

摘要

In this paper, 3D-CFD analysis has been utilized in order to provide sound information on the performances of a small turbocharged spark-ignition engine. In particular, the fluid-dynamic behavior of engine head and intake ports, still not in production, has been deeply investigated. The purpose of this analysis is to assess the cylinder filling, together with the ability to generate swirl and tumble motions as a way to improve the combustion efficiency, and ultimately the engine fuel economy. Initially, the 3-D CFD code, AVL-FIRE 8, has been validated by comparison with the experimental results obtained in a steady-state flow bench for the evaluation of key manifold characteristics like the flow coefficient and the turbulence indexes, for different computational domains (swirl configuration and tumble configuration) and valve lifts. These numerical simulations have given results in good agreement with the measured values, mainly in terms of flow coefficients. As expected, a diving-manifold provides a good filling and a macroscopic organization of the entering flow in the tumble plane; a swirling-manifold slightly impairs the flow coefficient, but provides a good organization of the intake air in the swirl plane. Furthermore, in order to better estimate the turbulence indexes, dynamic simulations have been performed, in which the engine operating cycle has been reproduced. In the end, the calculated turbulence indexes have been compared to the indexes of an engine head just for sale, providing interesting results. More specifically, the studied head revealed to be able to generate and, mostly, support the swirl motion until the start of combustion. Since this engine head was designed to implement the use of exhaust gas recirculation for load control in combination with the throttle-valve, this kind of behavior seems particularly encouraging. The high swirl levels allow tolerating relatively high EGR rates, avoiding misfiring phenomena, and assuring a regular combustion process.