Atkinsoncycle

The Atkinson cycle is a type of internal combustion engine cycle that prioritizes efficiency over power output, particularly at part-throttle conditions. Developed by James Atkinson in 1882, it modifies the traditional Otto cycle by altering valve timing. In an Atkinson cycle engine, the intake and exhaust valves are held open for a longer duration during the compression stroke than in a standard Otto cycle. This effectively creates a longer expansion stroke relative to the compression stroke. The primary benefit of this extended expansion is that more energy is extracted from the combustion of the fuel, leading to improved thermal efficiency.

This increased efficiency comes at the cost of reduced volumetric efficiency, meaning the engine may not fill its cylinders as completely with air-fuel mixture. Consequently, Atkinson cycle engines typically produce less power for a given displacement compared to Otto cycle engines. To compensate for this, Atkinson cycle engines are often paired with electric motors in hybrid vehicle powertrains. The electric motor can provide supplemental power when needed, allowing the Atkinson cycle engine to operate closer to its most efficient speed range. This combination leverages the Atkinson cycle's fuel economy for cruising and the electric motor's instant torque for acceleration. Many modern hybrid vehicles, such as those from Toyota and Ford, utilize variations of the Atkinson cycle.