Development of a New Intake System for a Small Spark-Ignition Engine. Modeling the Flow Through the Inlet Valve

The intake system of a wide commercial spread spark-ignition engine has been modeled by using a 3-D code. The present configuration of the inlet manifold and inlet port does not generate any organized charge rotation, especially at low rotational speed. Objective of this paper is the research of new solutions, able to produce higher turbulence levels of the in-cylinder flow, without lowering the engine volumetric efficiency, in order to shorten the combustion duration and improve the energy conversion quality. A three-dimensional model for the calculation of the inlet port and valve performance under steady conditions has been developed. First, the normal production intake system has been modeled to the aim of validating the model set-up. The inlet valve discharge coefficient in a steady flow has been calculated. The results obtained showed a good agreement to the measured data and encouraged the authors to use the model for the development of new intake solutions. The model has been adapted to different inlet manifold and inlet port and valve configurations in order to compare different solutions and determine the optimal geometry for the desired turbulence level. Furthermore, the steady flow data have been compared to the results of the unsteady flow through the valves in operating engines and the details of the flow field within the cylinder have been assessed as well.