Explosions Make the Wheels Go Round

by Deb on September 20, 2011


That’s the really short version of how internal combustion engines work. And if you find this through a search engine and are wondering how to fix or run one, sorry. I reliably keep the shiny side up and the rubber side down. I put the right fuel in. If absolutely necessary I can change the round things, even on a dirt track in the middle of nowhere. But that’s about it. This post is purely theoretical, because I think it’s hilarious that we get around by means of lots of tiny little explosions and I’m appreciative of how it’s changed our society.

The only thing more hilarious is bipedal walking, which is basically falling over then catching ourselves every.single.time.

Back to the explosions.


This diagram (from RKM.com.au) shows you what is happening in just one cylinder, the internal where the combusting happens. Working engines  have several cylinders (V6, V8, …) that are going at slightly different times so there’s always one firing.

The fuel you put in your tank is mixed with air – this used to be done by the carburettor but now it’s mostly electronic fuel injection – and feeds into the cylinder through a valve.

The piston is pushed up by the rod which squashes the air/fuel mix. In diesel this compression is enough to spark it by itself, but in petrol motors this is where the spark plug comes in. The fuel and oxygen burn very quickly and make gases that push out in all directions, otherwise known as an explosion. The sides of the cylinder are solid but the piston is moveable, so it gets pushed down.


This diagram shows the four stages the piston goes through.

  1. The fuel air mix going in.
  2. The compression and spark.
  3. The explosion pushing the piston down.
  4. The momentum and movement of other cylinders pushes it back up and the exhaust gases are pushed out, ready to start again.

As you can hopefully see in the diagrams, all this up-and-downing is converted to round-and-rounding because the shaft of the piston attaches to the side of a wheel. Using gears you can change the direction of the round-and-rounding and send it to the wheels.


And there you have the slightly longer possibly least technical ever explanation of the internal combustion engine.

I know that today they’re considered slightly evil and hopefully we won’t be dependent on them much longer. But take a few minutes to think about how different life was without them. I’ve spent the last 15 years in remote areas, and for those who aren’t in Australia that means hundreds of kilometres from towns or cities. Places where we get mail once a week and have to bulk order groceries because there’s no shop. And yet I know people who were living there when there was only a gravel road, and supplies came through every few months. It may take us five hours to get to the nearest airport, but it used to take them weeks (and there were no planes). The world is a much, much smaller place, and a lot of that comes down to the internal combustion engine.

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