Effects of Charge Motion Characteristics on Engine Variables such as Emission Behavior and Efficiency 2007-01-0640

Mixture formation in the combustion chamber is of paramount significance for diesel combustion processes. Particularly in inhomogeneous combustion processes with internal mixture formation, the course of combustion and composition of combustion products are heavily influenced by charge motion and material transport during the compression phase and during combustion itself. Charge motion is normally quantified in steady-state flow testing. This model-based test takes place under idealized conditions. This means that with a permanently open valve and constant pressure differential over the inlet port, a steady-state flow of air is established in the simulated cylinder. The influence of piston movement is neglected. The test delivers integral characteristic flow figures, such as swirl number, flow number and tumble number.

As flow measuring techniques continue to advance, spatially resolved data on the structure of the flow field and additional characteristic figures, such as information on the number and position of swirl centers and symmetry coefficients, are increasing the quantity of variables for assessing charge motion. Promising approaches also exist for measuring in-cylinder flow during transient engine operation. The fundamental relationship between charge motion determined under steady-state conditions and emission behavior and efficiency at the time of combustion is known. However, what is not known is the correlation between the structure of the flow field, as gained from steady-state flow measurement, and combustion.

This article describes the influence of characteristic flow figures on the one hand and the influence of flow field structure on the other. To this end, several cylinder heads with differing inlet port geometries are examined on a single-cylinder engine. The aim is to investigate the influence of individual flow characteristics on the combustion process under identical boundary conditions.