A Study On Characteristic Of In-cylinder Flow Field In SI Engine Under Un-throttle Control Method

Load could be controlled by unthrottle method while the variable valve actuation(VVA) is applied on the gasoline engine.We could control load in part load by cancel the throttle or keep it open all the time,control the air flux by change the valve lift but not the throttle.However,there would have great change in the engine working state while using VVA,especially variable valve lift,may have great effect on air motion.in order to study these characteristic, the in-cylinder flow field of a four-valve optical SI engine under different valve lifts is studied by PIV measurements.This research tested and evaluated the abilities of inlet of the cylinder head in the steady flow test bench. The results show that with the lowering of valve lift , the inlet have good flow ability,and the value of Cd is around 1,near to the theory value.Also test the inlet while one or two of the inlet is open find that the tumble ratio can be greatly enhanced at the end of intake stoke while only use one inlet port.The value of CF is consist of Cd,indicate that the cylinder head have good ability in inspiration.The optical SI engine is motored by the electromotor and three engine speeds(480r/min,720r/min and 960r/min)were examined,PIV measurements is used in the study of the air motion in-cylinder.The result indicate that the air velocity and kinetic energy can be increased while advance the engine speed,but there isn't big distinction in kinetic energy dure the end of the compress stroke.We could get lower tumble ratio and higher rotate ratio while use lower vavle lift,which can make intensity swirl motion.All the test condition can reach the biggest TR at about 120°CA ATDC,and SR about 210°CA ATDC. And it is also found that by compute of the turbulent integral length scale,a more uniformity field can be obtained by the use of higher vavle lift,this is good for gasoline mix,and the energy could assemble in the area under the intake vavle while use the lower vavle lift. By the mean time the in-cylinder prusure is measured in different condition,find that using the unthrottle method could reduce the intake loss,and it is about 20 to 40 persent in the test condtion.