Effect of Intake Valve Profile Modulation on Passenger Car Fuel Consumption

Variable valve actuation is a focus to improve fuel efficiency for passenger car engines. Various means to implement early and late intake valve closing (E/LIVC) at lower load operating conditions is investigated. The study uses GT Power to simulate on E/LIVC on a 2.5 L gasoline engine, in-line four cylinder, four valve per cylinder engine to evaluate different ways to achieve Atkinson cycle performance. EIVC and LIVC are proven methods to reduce the compression-to-expansion ratio of the engine at part load and medium load operation. Among the LIVC strategies, two non-traditional intake valve lift profiles are investigated to understand their impact on reduction of fuel consumption at low engine loads. Both the non-traditional lift profiles retain the same maximum lift as a normal intake valve profile (Otto-cycle) unlike a traditional LIVC profile (Atkinson cycle) which needs higher maximum lift. A non-traditional lift profile having a boot-type later closing was shown to offer the same level of fuel reduction as the traditional LIVC. In addition, a simpler solution has been explored where the LIVC with boot-type extension is featured on one intake valve (IV) in the cylinder, while the other IV features the normal closure. The investigation revealed that boot-type extension on one IV has the same potential to reduce fuel consumption as the traditional LIVC, with only a 11 crank angle degree (CAD) extension in duration compared to the latter. Furthermore, this solution is shown to have the potential to increase the region over which the engine can operate in Atkinson cycle compared to traditional LIVC.