Author Topic: The Atkinson Cycle engine  (Read 336 times)

Neil Ives

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Neil Ives

nowster

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Re: The Atkinson Cycle engine
« Reply #1 on: September 12, 2021, 08:35:21 PM »
https://en.wikipedia.org/wiki/Atkinson_cycle#Modern_Atkinson-cycle_engines
Quote
In the late 20th century, the term "Atkinson cycle" began to be used to describe a modified Otto-cycle engine—in which the intake valve is held open longer than normal, allowing a reverse flow of intake air into the intake manifold. This "simulated" Atkinson cycle is most notably used in the Toyota 1NZ-FXE engine from the early Prius.

The effective compression ratio is reduced—for the time the air is escaping the cylinder freely rather than being compressed—but the expansion ratio is unchanged (i.e., the compression ratio is smaller than the expansion ratio). The goal of the modern Atkinson cycle is to make the pressure in the combustion chamber at the end of the power stroke equal to atmospheric pressure. When this occurs, all available energy has been obtained from the combustion process. For any given portion of air, the greater expansion ratio converts more energy from heat to useful mechanical energy—meaning the engine is more efficient.

The disadvantage of the four-stroke Atkinson-cycle engine versus the more common Otto-cycle engine is reduced power density. Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an Atkinson-cycle engine does not take in as much air as would a similarly designed and sized Otto-cycle engine.

John Ratsey

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Re: The Atkinson Cycle engine
« Reply #2 on: September 13, 2021, 10:03:23 PM »
The lower torque and power are particularly noticeable on the Mk 3 Jazz which has an Atkinson cycle mode up to about 3000 rpm resulting in lethargic performance at lower revs but above that speed different valve operation made the vehicle more enthusiastic. On the Mk 4 Jazz the electric drive provides the torque and makes the deficiencies of the Atkinson cycle irrelevant.

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