Differences Between Atkinson Cycle and Miller Cycle
2 Answers
Below are the differences between the Atkinson cycle and the Miller cycle: 1. Different connecting rod mechanisms: (1) The Atkinson cycle has a complex connecting rod mechanism. (2) The Miller cycle does not have a complex connecting rod mechanism. The Miller cycle changes the compression ratio by altering the timing of the intake valve closure. 2. Different piston compression methods: (1) The Atkinson cycle compresses via the connecting rod mechanism. (2) In the Miller cycle, during piston compression, the intake valve closure is delayed, allowing some of the air-fuel mixture drawn into the cylinder during the intake process to flow back into the intake manifold, thereby altering the compression ratio.
Both the Atkinson cycle and Miller cycle are designed to enhance automotive engine efficiency and reduce fuel consumption. Their fundamental difference lies in the intake valve control method: The Atkinson cycle delays the closing of the intake valve, making the expansion stroke longer than the compression stroke, thereby extracting more energy from the fuel. However, its drawback is weaker power at low RPMs, often requiring electric motor assistance, as seen in Toyota hybrids. The Miller cycle closes the intake valve early and incorporates boosting devices like turbochargers to maintain sufficient air volume, avoiding power loss, making it suitable for high-performance models like Mazda. In real-world driving, I've tried two different cars—a Prius and an Atenza. The former is extremely fuel-efficient in city driving but slightly sluggish in acceleration, while the latter offers strong power with still-low fuel consumption. This design strikes a balance between environmental friendliness and economy, representing a significant step in automotive development.
