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The motivation of this paper is to describe the effects of variable valve timing (VVT) events on diesel engine performances. The paper describes an investigation into the effects of inlet and exhaust valve gas dynamics. In particular, effects on the pressure-volume cycle, and reverse flow through the intake and exhaust valves are studied. Computer simulation results show that VVT is much more useful for gasoline engines as compared with diesel engines for reducing the pumping losses. But, for diesel engines, VVT could be useful for the reduction of exhaust emissions such as NOx by using internal exhaust gas recirculation. The role of VVT in gasoline and diesel engines are described and compared.

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.