An Assessment of Intake and Exhaust Philosophies for Variable Valve Timing

In internal combustion engines, particularly for spark ignition (SI) engines, valve events and their timings put forth a major influence on the engine overall efficiency and its exhaust emissions. Because the conventional SI engine has fixed timing and synchronization between the camshaft and crankshaft, a compromise results among engine efficiency, performance, and its maximum power. By using variable valve timing (VVT) technology it is possible to control the valve lift, phase, and valve timing at any point on the engine map, with the result of enhancing the engine overall performance. To get full benefits from VVT, various types of mechanisms have been proposed and designed. Some of these mechanisms are in production and they have shown significant benefits for improving the engine performance. During the last two decades, remarkable developments have been seen in the field of VVT. This paper reviews the literature in the technology of intake and exhaust philosophies of VVT and their effects on the pressure-volume (PV) cycle of the engine. A single cylinder engine is simulated by the GT-Power software. The effects of different VVT philosophies from the simulations are analyzed and compared to those of the literature reviewed.