What is the principle of the Atkinson cycle engine?

[AdrianaDella]

The working principle of the Atkinson cycle engine is to extend the power stroke and shorten the compression stroke, making the expansion ratio greater than the compression ratio, thereby more effectively utilizing the residual high pressure of the exhaust gas after combustion. The fuel and air mixture burns, generating heat energy, and the gas expands when heated, converting into mechanical energy through mechanical devices to perform external work. Below is more information about the Atkinson cycle engine: 1. Introduction: The Atkinson cycle engine improves efficiency but reduces power density, with the drawback of lower efficiency and poorer torque at low speeds. 2. Application: The Atkinson cycle engine is currently used in some hybrid vehicles. Hybrid vehicles are those powered by two or more energy sources, and the drive system can have one or more sets. Common energy sources include fuel, batteries, fuel cells, solar cells, compressed gas, etc., while common drive systems include technologies such as internal combustion engines, electric motors, and turbines.

[VonCatherine]

Speaking of the Atkinson cycle, I think it's a real 'energy-saving expert'. In a conventional engine, the four strokes of intake, compression, power, and exhaust are symmetrical. But Atkinson played a clever trick—it ingeniously delays the closing of the intake valve through the engine's valve train, allowing some of the sucked-in air to be secretly 'spit' back into the intake pipe when the compression stroke begins. This means the actual compression stroke of the piston becomes shorter, consuming less energy, while the expansion stroke remains complete or even becomes longer, greatly improving energy efficiency. Many hybrid vehicles today, like Toyota's hybrid system, love using it precisely to squeeze the maximum out of every drop of fuel, making them particularly fuel-efficient. However, this design sacrifices some power explosiveness, relying entirely on the electric motor to compensate during acceleration.

[MacLily]

Friends who have driven hybrid vehicles must have heard of the famous Atkinson cycle. Its core trick is to shorten the compression stroke and extend the expansion stroke, which sounds a bit complicated, right? Simply put, it involves keeping the intake valve open longer to release some of the air sucked into the cylinder before compression. This is like making the compression action 'lazy and do less work,' while fully utilizing the expansion force after combustion. It's similar to saving energy at the start of a run and then fully pushing off in the latter half. In practical driving, this means it's particularly suited for steady cruising to save fuel. Paired with the hybrid system using electric power at low speeds, the fuel efficiency is impressively low. However, if you suddenly floor the accelerator to overtake, it feels a bit sluggish.

[OJoy]

In all my years working with engines, I've been most impressed by Atkinson's 'philosophy of laziness.' In the traditional Otto cycle, the compression and expansion strokes are of equal length, but Atkinson altered the valve timing to make the compression stroke shorter than the expansion stroke. It's like tightening a screw—saving some effort in the first half-turn and then applying full force in the second half. This ingeniously addresses the engine's flaw of 'wasting fuel during compression while not fully utilizing the energy released during combustion.' The trade-off is slightly lower torque at low RPMs, which is why hybrid vehicles use electric motors to compensate for this. Fuel consumption can be reduced by at least 15% compared to conventional engines.