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What is the Atkinson Engine and is it any good?

What is the atkinson engine, and how does it perform compare to other engines?

Filed under hybrid - Asked by John Carey (Clogheen) - Mon, 15 Aug 2011 21:01


Answer

Hi John, 

The Atkinson engine is a type of engine invented by James Atkinson in 1882. The Atkinson Cycle is where the stroke of the piston can very in length across the four cycles in a four-stroke internal combustion engine. The length of the stroke during the power cycle is increased to promote efficiency, but because this comes at the expense of a shorter intake stroke there is some loss of power and therefore this engine design is best suited for use in hybrid systems where the electric motor can make up for some of the loss of power. 

In conventional four-cycle petrol engines, fuel enrichment is sometimes necessary to cool the exhaust gases, preventing degradation or destruction of the catalytic converters. In an Atkinson cycle engine, compression and expansion are not symmetrical, and the valves close late, delaying compression. This creates a high expansion ratio for less compression, reducing intake and exhaust energy losses and converting combustion energy to engine power more effectively. As a result, the exhaust temperature is lower than that of conventional engines.

The current model Toyota Prius Hybrid uses a 1.8-litre Atkinson Cycle engine. Adopting the Atkinson cycle and a cooled exhaust gas recirculation system brings significant gains in fuel efficiency and emissions reduction.

Prius 1.8-litre Atkinson Cycle engine

Because the intake valves close late in an Atkinson cycle engine, compression is delayed. This creates a high expansion ratio for less compression, reducing intake and exhaust energy losses and converting combustion energy to engine power more effectively. As a result the exhaust temperature is lower than that of conventional engines. Cooled Exhaust Gas Recirculation reintroduces the cooled gas into the intake system, further reducing engine operating temperatures.

Other models to use Atkinson Cycle engines include the Lexus CT200h, Lexus RX 450h, Mercedes S400 Blue Hybrid

Answered by: Complete Car Adviser

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