Study On Numerical Simulation Of The Variable Swirl Intake System On Intake Flow Characteristics For DI Diesel Engine

Variable swirl intake technology can improve performance of engine at a wide speed range by organizing variable swirl intake flow. This paper developed a variable swirl intake system for a 2.0 liter four-valve DI diesel engine. This system can produce suitable intake air motion to meet the requirement of swirl ratio at different operating conditions, which can improve the engine power and efficiency and reduce the exhaust emission.Firstly, intake resistance and energy loss of air intake system were analyzed, and the effect of intake swirl in the promotion of quality of mixture and engine performance was studied. Design principles and the specific method of variable swirl intake system were researched for this engine.The theory of CFD (Computational Fluid Dynamics) assisted in intake system of engine analysis was studied. The three-dimensional steady simulation of airflows in the inlet port of diesel engine was performed by using simulation software AVL-FIRE. The simulated flow field provided detailed information of different inlet ports on flow characteristics and swirl characteristics. The results showed that the flow of two inlet ports can interfere with each other, which will cause the loss of flow capacity, and the difference swirl characteristics of different inlet port provides the possibility to achieve variable swirl.The variable swirl intake system was developed for this four-valve DI diesel engine, and two different options of swirl control system were proposed. A three-dimensional steady CFD model which includes air intake manifolds, swirl control valve (SCV), inlet ports, intake valves and cylinder was established. Flow coefficient and swirl ratio at different opening of SCV were calculated. The optimal option is selected by analyzing the simulation results of different options. The results showed the variable swirl intake system could change the swirl ratio and give some adjustment to the swirl and flow coefficient. Option one had a better effect because of its wide variable swirl range and low energy loss of intake flow. It can meet the requirement of swirl ratio under different operating conditions.A one-dimensional simulation model for this diesel engine was established and simulated by using simulation software AVL - BOOST. The intake flow characteristics and swirl characteristics of engine under different speed conditions were studied. The results show that intake flow and swirl ratio increased with the increasing of engine speed, and throttling losses of SCV at low speed is not obvious, throttling losses become greater with the increasing of engine speed. So that it is feasible to change the swirl ratio by using variable swirl intake system to meet the need of swirl at different operation condition.This paper is about the study on numerical simulation of the variable swirl intake system on intake flow characteristics and swirl characteristics. This paper has some reference value in design and analysis of variable swirl intake system for diesel engine.