Experimental analysis of the tumble generation process in the intake system of a 4-valve SI engine

This paper describes an experimental analysis performed to evaluate the flow characteristics of the intake system of a high performance 4-valve Spark Ignition engine, analyzing the influence of different experimental conditions at the steady flow test bench and the potentialities of different valve lift strategies. Experimental tests are performed at different pressure levels on a Ducati Corse racing engine head, to measure the Discharge Coefficient Cd and the Tumble Coefficient NT, expanding the work already presented in a preceeding work: the maximum test pressure level is increased up to 24 kPa by means of a new test bench, while differently-shaped tumble adaptors are used to evaluate NT. The study is aimed at evaluating the influence of the test pressure and of the tumble adaptor shape on Cd and NT measurements. As a matter of fact, different tumble adaptor shapes are found in literature, such as the conventional T type or the L one, resulting in a non uniform base to compare results from different investigations. This work is aimed at verifying the quantitative differences that can be found by using these shapes. The analysis highlights also the significant differences which have been found in the Cd values obtained in the different test conditions. Peculiar attention is also paid to the analysis of the influence of asymmetric valve opening strategies on the tumble intensity. Interesting results have been found analysing low lift combinations (useful for VVA part-load operation), that allow to obtain higher tumble values, if compared to conventional two valve lift strategies, by keeping constant the discharge coefficient values.