Influence of the intake system design on a small spark-ignition engine performance a theoretical analysis

In a previous paper, the authors assessed the potential of CFD modeling in developing a new intake system for a small spark-ignition engine. The effect of the intake port and valve design on the charge motion within the cylinder was illustrated [1]. In this paper, a detailed analysis of the influence of the intake port geometry on the combustion process, therefore on the performance, of a MPI spark-ignition engine has been carried out. The purpose of such a theoretical analysis is to provide some guidelines, in developing new intake solutions, aimed to improve the combustion quality of a production engine on the market since the early 80's. A 3-D computer code has been used to model the intake, compression and combustion processes of the engine. The model has been validated comparing the computational results to the data, relative to the normal production engine, provided by the manufacturer. Then, the model has been employed to assess the behavior of different intake port geometries, proposed by the authors, to the aim of increasing the turbulence level within the cylinder. The final goal of the proposed modifications is to accelerate the combustion process, without re-designing the combustion chamber, in order to achieve better engine efficiency and emissions. Copyright © 2003 SAE International.