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

摘要

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.