A CFD Investigation into the Effects of Intake Valves Events on Airflow Characteristics in a Motored 4-Valve Engine Cylinder with Negative Valve Overlapping

This paper presents a computational study of the airflow features within a motored 4-valve direct injection engine cylinder. An unconventional intake valve strategy was investigated; whereby each valve on the pair of intake valves was assumed to be actuated with different lifts and duration. One of the intake valves was assumed to follow a high-lift long duration valve-lift profile while the other was assumed to follow a low-lift short duration valve-lift profile. The pair of exhaust valves was assumed to be actuated with two identical low-lift short duration valve-lift profiles in order to generate the so-called negative valve overlapping (NVO). The in-cylinder flow fields developed with such intake valve strategy were compared to those produced in the same engine cylinder but with the application of identical low-lift short duration intake valve events. The computational results of such an approach showed a considerable modification of the intake generated cylinder-averaged swirl and tumble motions. Besides, utilizing this intake valve strategy with a difference in phase between timings of the high-lift and low-lift intake valves revealed an enhancement in the induction-produced turbulence characteristics. Applying such intake valve strategy in real-life 4-valve engines is expected to improve the combustion aspects of both spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion systems.