An Experimental Investigation On Tumble Ratio Measurement In Gasoline Engines

The in-cylinder flow is one of the many important factors which significantly affect the combustion process,the power performance,fuel economy,and emission of engines.The inlet port plays a key role in the formation of macroscopic motion(tumble and swirl)and turbulence level during the late stage of the intake stroke,and makes a vital impact on the engine performance.Steady flow test rigs are often used to evaluate the port performance.Firstly,the influence of measurement devices and different evaluation methods on the tumble ratio is studied using a swirl torque meter and paddle wheel anemometer on a steady flow rig,respectively.Further,a three-dimensional particle image velocimetry(3D-PIV)system is used to measure the three-dimensional velocity fields.The results show that the high out-plane velocity field is formed by two jets which flow through the intake valves.One of the two jets is strong and the other is weak.When these two jets met with each other and the collision results the large-scale vortices flow in right-about compared to the main flow in the measurement plane.The flow symmetry under the small valve lift is poor,and it increases with the valve lift.Secondly,based on the three-dimensional velocity fields,two evaluation methods of tumble ratio are proposed from the view of the characteristics and evolution of tumble flow.The results show that the tumble ratios obtained using the 3D-PIV are larger than that obtained using the test rig.The reasons are that,on the one hand,the measurement plane is 0.5B from the cylinder bottom.On the other hand,the 3D-PIV direct measurement method decreases the local flow resistance because the orthogonal head of the simulate cylinder and the paddle were abandoned.In addition,both of these two evaluation methods using 3D-PIV could show the variation of the tumble ratio objectively no matter whether the tumble is strong or weak.However,the tumble ratios obtained by the method based on the theoretical airflow rotate speed and the theoretical engine speed using 3D-PIV are non-monotonic and have a local maximum value under small valve lifts.The local maximum value under small valve lift is higher than that under large valve lift.Therefore,this method cannot reflect the variation of the tumble ratio exactly.While the tumble ratio obtained by the method based on theoretical tangential speed and theoretical axial speed using 3D-PIV increases with the valve lift and it is reasonable relatively.Therefore,the second method using 3D-PIV is more reasonable.