Numerical Simulation Research On The Cylinder Flow Field Of The Variable Swirl Intake System

The rapid growth of the car ownership cause serious environmental pollution and energy crisis.Which urgently request countries to pay attention to improving energy conservation and emissions reduction technologies.Air intake system as an important part of engine,can not only provide enough air volume for cylinder,but also provide requiredvortex intensity to the engine according to the shape of the inlet.Good air movement characteristics in cylinder not only improves the flame speed,at the same timeit also plays an important role to adapt to the stratified charge or lean burning.Therefore,further studying the variable swirl intake system and the effect of the vortex valve plates on the air motion inside the engine cylinder,and choosing reasonable valve opening according to engine crank angle,have important directive significance in improving the combustion process in the cylinder and developing high performance and low pollution engine.Whenworking conditions of engine changes,the requirements for swirl intensity in cylinder changes at the same time.The variable swirl intake system can provide continuously variable intake flowrate andswirl intensity for the engine according to the working conditions.In this paper,the four valve straight engine is research object and computational fluid dynamics is research method.The research of the variable swirl intake system as follows:Firstly,establishing the geometric model of air intake system,using three-dimensional modeling software CATIA to establish the model including inlet,valve and cylinder.Then several common turbulence model are used to simulate the air intake system and the optimal turbulence model is selected for inlet numerical simulation.After that,installation position of variable vortex valve plates in the inlet issimulated.The results between two different installation position are analyzed and it can provide a design basis for the variable swirl intake system.And then the heightof vortex valve plate was studied,and selecting the optimal height for inlet system.And last,the opening of the valve plates was simulated under different engine running conditions and the effectof valve opening on mass flow and turbulence intensity in the cylinder was analyzed,the influence law of airflow in cylinder affected by valve opening was obtained,which provide the design basis for the variable swirl intake system.The followed conclusions were obtained from the study.(1)Installation positionof the valve has an important effect on the airflow in the cylinder.Installing in the branch inlet can increase cylinder turbulence intensity by 20%;(2)The higher of the vortex valve plate,the lower the pressure and the greater the turbulent kinetic energy in cylinder;(3)The valve opening affect the flow field distribution in cylinder.When the valve opening become large,the flow area of the inlet will decrease.This would lead to more pressure gradient.So intake resistance will increase,and the pressure in the cylinder reduce and tubulence energy increase.Turbulent kinetic energy in cylinder increase by 49% when the maximum valve opening,at the same time the average pressure in cylinder reduce 3 KPa,which will reduce volumetric efficiency;(4)When the crankshaft rotation speed increase,the piston downward speed increase as well,the average pressure in cylinder will decrease and turbulent kinetic energy will increase.All of the parameters change on the contrary when the crankshaft rotation speed reduce.So the valve opening should decrease at high crankshaft speed to provide adequate air inflow for cylinder and increase at low crankshaft speed to increase turbulent kinetic energyin cylinder.