James Atkinson, a British Engineer, developed an engine in 1886 that was about 10% more efficient than the engines developed by Nikolaus Otto in 1876. It is unclear whether efficiency was Atkinson’s intended goal or he intended to simply come up with a different design that would not infringe on the patents of Mr. Otto. In any case, due to it’s complexity, the Atkinson design did not become too popular.
Most of today’s automobile engines are of the Otto Cycle variety.
None the less, the Atkinson Cycle engine is unique in that it employs a complex mechanism which results in intake and compression strokes that are shorter in length than the power and exhaust strokes.
More recently Toyota has developed an Atkinson cycle engine for use in the Toyota Prius hybrid vehicle. Although it achieves the Atkinson cycle equivalent due to valve timing and not through actual stroke length differences due to mechanics. The result is a more efficient engine (although also lower power for the same size and weight).