A Study on the Effect of Intake Port Modification to Improve the In-Cylinder Flow Characteristics of Small Motorcycle Engine

Abstract

The in-cylinder flow is one of the important factors that affect the quality of air-fuel mixture in engine. One parameter that affect the in-cylinder flow is intake port design. In this study the effect of intake port modification was investigated to improve the flow characteristics of small motorcycle engine. An experimental system with a steady flow bench for a variety of valve lifts at two pressure drops of 300 and 600 mmH2O was installed and a simulation model based on CFD method was setup. Moreover, the modification of intake port based on the flow direction and inclination angle were investigated to improve the flow characteristic of small motorcycle engine. Looking at the results, the intake port with 15º and 30º increase the flow coefficient compared to the original port of 2.46% and 6% respectively. The increase of pressure drops increases the flow velocity by two times to 100 m/s and make the vortex core to move closer to the cylinder axis. Increase in pressure drop at the beginning of valve lift appeared to have no effect on the swirl ratio until the valve lift reached 5 mm. However, the swirl ratio got a 25% reduction when the valve lift reached 6.25 mm. The flow velocity maximum of the tangential port is almost double compared to the all helical models at 60 m/s. The tangential port with all inclination angle has same flow velocity maximum of 60 m/s in the center of cylinder. However, the port 30º has a more even distribution of velocity magnitude in all directions compared to other models. In the vertical plane, the greatest flow velocity occurs at the 6.46 mm valve lift at port 30º and 15º at 78.5 m/s on the upper side of the cylinder near the intake port. Compared to other models, port 30º has the most turbulent kinetic energy, length scale and kinematic viscosity with an increase of 9.55%, 4.65% and 15.25% respectively compared to the original port. Based on this case study, the tangential port 30º is the most optimal port compared to other models where this port has a better increase in flow velocity and vortices which results in increased turbulence in the cylinder. The increased turbulence is expected to result in a more homogeneous mixing of air-fuel in the cylinder engine.