How a Modern 4-Cycle Works

Picture
  • Perhaps the most common application of the Otto Cycle today is in the modern automobile engine.
  • This picture on the left depicts the 4 phases of a generalized 4-stroke engine. 
  • The 1st phase, called the intake phase, is when the piston moving downwards pulls in the mixture of fuel and air used to combust. 

  • In the compression phase, the piston moves upward in the sealed combustion chamber, compressing the fuel/air mixture. 
  • In the 3rd phase, more commonly known as the "power stroke", is when the spark plug ignites the fuel/air mixture just as the piston continues reaches the top of its 2nd turn and continues downward.
  • In the exhaust stroke, the exhaust valve is opened, allowing the piston to push out the the used fuel through to the exhaust port.