Abstract
This paper examines the major influence of intake system characteristics on the fuel-air-mixing, combustion process and emissions. There are four ways to reach an optimization of internal process of engines: dimension characteristics on intake manifold, intake channels, intake parts and intake valves. These components of the intake system can modify the macro and micro level of motion in the engine cylinders. Choosing the optimal dimensions of the intake manifold there can be obtained a resonant system, which uses the Helmholtz effect (ram effect) to increase the effective volumetric efficiency at tuned speed. The presence of amplified pressure waves at the level of the intake part generates during intake stroke waves, which remain also during compression stroke. These waves amplify the turbulence motion of fresh charge and contribute to the improving of an intimate air-fuel-mixing process (micro mixing effect). The research developed to obtain different levels of swirl motion, and, for this, two ways were used: intake channels (tangential channels and helical channels), shrouded intake valves. As optimal swirl ratio provides the most of quantity of fresh air to be used in the air-fuel-mixing and combustion process (macro mixing effect). The intake port design has an important influence on the speed field of airflow during the intake stroke, which generates different levels of turbulent motion, which has the same effect as the pressure waves generated by a resonant intake manifolds.