Four-stroke engine

Periodic Table

1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum (negative pressure) in the cylinder through its downward motion.
2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is ignited by a spark plug (in a gasoline engine) or by heat generated by high compression (diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust port.

Double-acting stationary steam engine demonstrating conversion of reciprocating motion to rotary motion. The piston is on the left, and the crank is mounted on the flywheel axle on the right

Diagram of a cylinder as found in an overhead cam 4 stroke gasoline engine: C – crankshaft E – exhaust camshaft I – inlet camshaft P – piston R – connecting rod S – spark plug V – valves. red: exhaust, blue: intake. W – cooling water jacket Gray structure – engine block

A mechanical wave, also called a matter wave, is a propagation of energy through matter. The wavelength is the distance between two consecutive peaks (the highest part of the wave). On this graph, the x-axis is distance and the y-axis is the displacement of matter. Water waves, sound waves, and waves on a rope are all examples of mechanical waves.


Light waves, also called electromagnetic waves, involve oscillations of electric and magnetic fields rather than oscillations of matter. The wavelength is its color. On this graph, the x-axis is distance; the y-axis is the strength of the electric field; and the z-azis is the strength of the magnetic field. Light waves include all forms of electromagnetic radiation: gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves.