ATKINSON cycle engines are commonplace today in petrol-electric hybrids. However, these modern Atkinson cycle engines are very different to the original Atkinson cycle engine(s) which date back to the 1880s, even if they do share a common principle.
James Atkinson came up with a number of designs, the most famous of which managed to provide intake, compression, power and exhaust strokes in one revolution of the crankshaft via a complex linkage arrangement. Conventional Otto cycle engines need two revolutions of the crankshaft to achieve the same thing.
All of Atkinson’s designs had one thing in common, namely the compression stroke was shorter than the power stroke. Modern Atkinson cycle engines achieve a similar effect by delaying the closing of the intake valves until after the start of the compression stroke. This leads to improved thermal efficiency when power production isn’t paramount.