Revolutionary Engine Design - How Atkinson Compares with Miller & Otto Engines
We look at how an engine works, detailing the OTTO cycle and compare this against the newer revolutionary Miller and Atkinson cycle engines.
Can you tune a Prius? We look at the Atkinson engine, how it works and explain what this engine is really good at and what it's weak spots are.
What is the difference between Miller and Atkinson cycle engines? How to Miller and Atkinson engines compare with OTTO cycle engines.
In this video, we dive deep into the workings of internal combustion engines, starting with the familiar four-stroke process – commonly referred to as "suck, squish, bang, and blow." We’ll break down each stage of this traditional Otto cycle engine, which powers most combustion engines today. But we're not stopping there. We'll also explore the differences and advantages offered by the more advanced Miller and Atkinson cycle engines.
First, we'll cover how the typical internal combustion engine works through its four strokes. It starts with the intake stroke, where the air and fuel mixture enters the cylinder. Next, the compression stroke sees the piston compressing this mixture, preparing it for combustion. Then comes the power stroke, where the spark plug ignites the mixture, causing an explosion that pushes the piston down, which in turn powers the engine. Finally, the exhaust stroke pushes the burnt gases out of the cylinder, making room for the cycle to repeat. This is the foundation of the Otto cycle, named after its inventor, Nikolaus Otto, who developed it in 1867.
However, engine technology didn’t stop evolving. In the 1940s, new designs emerged, notably the Atkinson and Miller cycle engines. These engines introduce a key difference: they leave the intake valve open longer during the compression stroke, shortening it and increasing overall efficiency. This trade-off results in less power but dramatically improves fuel efficiency, as the piston does less work compressing the air-fuel mixture.
But what sets the Atkinson and Miller cycles apart? The Atkinson cycle engine is typically naturally aspirated and focuses on maximizing fuel efficiency. The Miller cycle, on the other hand, uses forced induction, such as a supercharger, to compress air into the cylinder. This means that the supercharger, rather than the piston, handles much of the compression work, allowing the pistons to move more efficiently.
The Miller cycle’s use of forced induction comes with its own set of challenges. For one, the turbocharger or supercharger needs to build up pressure before it can offer more power. This delay means that at lower RPMs, the engine produces less power. Additionally, the increased complexity of these systems – with added components like intercoolers – makes the engines more expensive to develop and maintain.
In contrast, the Atkinson cycle keeps things simple, completing all four strokes in one full crankshaft rotation. This setup results in lower compression and higher efficiency, which is why it's commonly used in hybrid vehicles. However, with lower compression comes lower power output, making Atkinson cycle engines less suited for performance applications.
Can you tune a Miller or Atkinson cycle engine for more power? Technically, yes, but it's generally not worth the effort. These engines are designed for efficiency, not performance. Modifying them to increase power output would go against their intended purpose, and you would lose the fuel savings they provide.
Some engines, like the one in the Honda Fit, combine the best of both worlds. These advanced designs can switch between Otto and Atkinson cycles, optimizing for power or efficiency depending on driving conditions.
By the end of this video, you'll not only understand how traditional internal combustion engines work but also appreciate the innovations that Atkinson and Miller cycle engines bring to the table, especially in the quest for greater fuel efficiency. Whether you're interested in how these designs make engines more efficient or want to understand the trade-offs between power and economy, this video covers it all.
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Footage Credits
iStock,com/Pathompong Thongsan
iStock,com/cinejinn
British Motor Museum
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