Impact of Tumble on Combustion in SI Engines: Correlation between Flow and Engine Experiments

The introduction of tumble into the combustion chamber is an effective method of enhancing turbulence intensity prior to ignition, thereby accelerating the burn rates, stabilizing the combustion, and extending the dilution limit. In this study, the primary intake runners are partially blocked to produce different levels of tumble motion in the cylinder during the air induction process. Experiments have been performed with a Chrysler 2.4L 4-valve I4 engine at maximum brake torque timing under two operating conditions: 2.41 bar brake mean effective pressure (BMEP) at 1600 rpm, and 0.78 bar BMEP at 1200 rpm. A method has been developed to quantify the tumble characteristics of blockages under steady flow conditions in a flow laboratory, by using the same cylinder head, intake manifold, and tumble blockages from the engine experiments. A refined tumblemeter is installed under cylinder head to measure the compressive load of the tumble vortex, allowing for the calculation of angular momentum of the incoming air, tumble number, and tumble ratio at varying intake valve lifts. A correlation is then sought between the engine and flow experiments to help quantify the impact of tumble motion on combustion and cyclic variation. The air flow rate into the cylinder, discharge coefficient of the intake system, and the flow loss coefficient across the blockage are also analyzed for different levels of tumble motion. The validity of the method under steady flow conditions is confirmed by comparison of the results with the engine experiments.