Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
Most automobile manufacturers have developed hybrid vehicles that combine an internal combustion engine and an electric motor, fusing the advantages of these two power sources. For example Toyota in its Prius II uses a gasoline engine which achieves high efficiency by using a modified Atkinson cycle based on variable valve timing management. This implementation of the Atkinson cycle is not the optimal solution because e.g. some of the air is first sucked from the intake manifold into the cylinder and subsequently returned. This oscillating air stream considerably reduces the thermal conversion efficiency of this cycle. In this paper the losses in the thermal conversion efficiency of internal combustion engines, and especially of Atkinson cycles, are analyzed in detail and a proposal for an improvement cycle for such applications is made.