Study of Swirl Ratio on Mixture Preparation with a Swirl Control Valve in a Diesel Engine

摘要

Downsizing as a main-stream technology was widely used for design of future diesel engines in order to meet the increasingly stringent demands of emissions regulation and reduction of CO_2 production. Design of intake system faces a considerable challenge accordingly. Discharge coefficient and swirl ratio as two main factors of intake port design have been widely investigated by researchers. However, these two parameters indicate a trade-off relationship. Therefore, it is difficult for a classical intake system to achieve a good balance between sufficient air charge and decent air-fuel radial mixing quality. A 1 L twin-intake-port single-cylinder diesel engine was studied in this paper. A swirl control valve designed to adjust the effective flow area of the filling port, was installed between the intake manifold and the intake filling port in order to achieve variation of swirl ratio. And there is no control valve for the intake spiral port. Influence of varied angles of the swirl control valve on the discharge coefficient and the swirl ratio of intake ports were firstly investigated on a steady flow rig. Then Particle Image Velocimetry (PIV) technique was used to visualize the in-cylinder swirl motion. Besides, CFD method was used to evaluate the effects of varied valve angles on the following air-fuel mixing process in the cylinder. The results show that CFD reveals the in-cylinder flow structure and the location of swirl center similar with the 3D-PIV test results. With the increase of swirl ratio at IVC from 0.57 to 2.05, air-spray interaction in the circumferential direction is strengthened in the terms of mixture preparation. Strong swirl motion accelerates the heat release during the premixed combustion stage, which results in an advancement of CA50 and a reduction of combustion duration. High swirl motion intensity makes a positive effect on the increase of accumulated heat release under the same air flow mass rate.