A visual particle image velocimetry(PIV) test system was set up for the in-cylinder flow field measurement of a 3-cylinder gasoline engine. On this basis a test method for tumble ratio calculation at different flow field cross section was studied

and the test results were compared with the simulation data. Results show that the transversal velocity field in the cylinder measured by 2D3C PIV test is consistent with the simulation data calculated by using AVL FIRE software. Flow coefficient and tumble ratio obtained by test measurements and simulation calculations are in agreement along with the change trend of valve lift

and the error is within a reasonable range. The 2D2C PIV test can be used to measure the velocity field at different cross section of the cylinder to show the variation of the 3D flow field in the cylinder

in which the valve axisymmetric velocity field can be well used to characterize the motion state of the tumble flow. In addition

the transversal velocity field can be synthesized by the equally spaced axial cross-sectional velocity field and rotary axial cross-sectional velocity field measured by a series of PIV measurement. The velocity distributions and the gradient field change trend are the same as that of the transversal velocity field measured by 2D3C PIV test

but the measured tumble flow ratio is smaller than the calculated value.