Insights into the development of the tumble motion using the direct and indirect steady-flow test methods

The measurement and evaluation of the tumble motion in an engine cylinder are widely achieved by steady-flow tests. However, there is absence of a standard methodology for the evaluation of the tumble motion in the steady-flow tests. The aim of this paper is to analyse the variation in the evolution of the tumble motion with different tumble test methods. Both steady-flow tests and particle image velocimetry measurements were carried out on a commercial four-valve spark ignition engine. The results showed that, for the indirect test method, the variation in the diameter of the cross pipe has a negligible effect on the non-dimensional tumble intensity, although the angular momentum flux is proportional to the diameter of the cross pipe owing to the conservation of the rotational kinetic energy flux. For the direct test method, there is an obviously abrupt rise in the tumble intensity with increasing valve lift because the in-cylinder flow evolves into a single large-scale tumble vortex in a short transitio...