GoKawiilThe invention of the internal combustion engine in the 19th century has revolutionized transportation over land, water, and air. Despite their omnipresence in modern day, the operation of an engine may be cryptic. Over the course of this article I’d like to explain the functionality of all the basic engine parts shown in the demonstration below. You can drag it around to see it from other angles:
It’s hard to talk about a mechanical device without visualizing its motion, so many demonstrations in this blog post are animated. By default all animations are enabled, but if you find them distracting, or if you want to save power, you can globally pause them.disabled, but if you’d prefer to have things moving as you read you can globally unpause them.
An engine like this may seem complicated, but we will build it up from first principles. In fact, we’ll start with a significantly simpler way of generating a rotational motion.
Crank
Let’s look at a simple crank. It consists of a handle, a crank arm, and a shaft. When a force is applied to the handle the shaft rotates which we can observe by looking at the attached disk:
The force applied at a distance from the shaft generates torque. The harder we push on the handle, the bigger the torque on the shaft. This cranking mechanism is precisely what converts linear force into torque in a manual coffee grinder or a bicycle.
It’s one thing to power something using our own muscles, but the entire point of building an engine is to avoid manual labor and have the device exert the effort instead. To do that we need to find a reliable source of a strong force that is easy to direct. Thankfully, such device was invented hundreds of years ago – a cannon does exactly what we need. In the demonstration below you can observe how a cannon ball is fired from a cannon. The diagonal lines indicate a cross section view – it lets us see what’s going on inside an otherwise obscured region:
As the gun powder is set on fire it quickly produces a huge amount of gases, which push the cannon ball down the barrel. Since the ball snugly fits inside it can only go in one direction. While reliable and easy to direct, a cannon ball won’t be very effective at pushing the crank:
We’ve only been able to do a partial turn of the shaft and the cannon ball is long gone. However, with a few modifications we can harness the pushing power of the explosion in a significantly better way.
Firstly, we’ll replace a cannonball with a piston that has a cylindrical shape and a hole drilled in it. We’ll then use a pin to attach to it a rod that can swing freely on a crankshaft:
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