Knowledge of the relevant cause-effect relationships for the combustion process, such as the interaction between the in-cylinder flow and the combustion behavior, are becoming essential for future combustion engines. Apart from the general interdependencies between the combustion rate and the turbulence intensity, specific combustion concepts, known from lean-burn engines, also strongly depend on the global flow structure which for example controls the mixing processes.
Particle tracking velocimetry (PTV) was used to analyse the bulk in-cylinder flow of multi-valve production engines. The PTV results gave rise to well-aimed modifications of the intake ports and thus of the in-cylinder flow in order to achieve an optimized mixing of the charge or to affect the turbulence production during the compression stroke. Various intake-port configurations, such as high and low tumble concepts or swirl-generating systems, including intake-port deactivation, had been examined during motored engine operation at 2000 rpm. The PTV flow field photographs from different measurement planes were taken during induction as well as the compression stroke.
The particle tracks on these photographs clearly revealed the large-scale flow structures which contain kinetic energy to be transformed into turbulence. Results from the in-cylinder flow measurements were related to the firing engine performance while the operation conditions corresponded to the PTV measurements. This analysis included the thermodynamic behavior and the flame propagation through-out the combustion chamber.