We all learn the theory of what happens inside an internal combustion engine; a mixture of fuel and air is ignited by a short electric spark. Some people describe the ensuing event as an explosion, but the ideal is a controlled burn, but it's still so fast that it could be confused for an uncontrolled explosion. An engine is a practical application of thermodynamics, when it comes right down to it. The piston moves by the pressure exerted by the burning fuel mixture, and as the piston moves down the bore, pressure reduces, and work is extracted from the fuel.
Of course, there's a lot more to it, but that's the basics. We're sure you had a little animated diagram dancing around in your head the first time you really tried to understand the common Otto cycle. My mental flash player still fires up when I'm trying to figure out different cycles like the Atkinson. Wouldn't it be great to actually
inside the cylinder during combustion events? No, we didn't videotape our lawnmower with a
plug -- this technique is far fancier.
Video and technique info after the jump