1. The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work.
  2. Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful.
  3. When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down.
  4. Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe.

With a diesel motor only air is taken in during the intake stroke then at the peak of the compression cycle the fuel is then added so the pressure ignites the engine and not the spark plug.

Hope this little over view was interesting. If you show interest and decide to continue on learning more about Amsoil Synthetic Lubricants there is a lot on my site to read about.