Four Stroke Engine
The four stroke engine was first demonstrated by Nikolaus Otto in 18761, hence it is also known as the Otto cycle. The technically correct term is actually four stroke cycle. The four stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks.
The four strokes of the cycle are intake, compression, power, and exhaust. Each corresponds to one full stroke of the piston, therefore the complete cycle requires two revolutions of the crankshaft to complete.
Two Stroke Engine
The two stroke engine employs the crankcase as well as the cylinder to achieve all the elements of the Otto cycle in only two strokes of the piston
Wankel Engine
The Wankel radial engine is a fascinating beast that features a very clever rearrangment of the four elements of the Otto cycle. It was developed by Felix Wankel in the 1950s.1
In the Wankel a triangular rotor incorporating a central ring gear is driven around a fixed pinion within an oblong chamber.
Atkinson Engine
The Atkinson engine is essentially an Otto-cycle engine with a different means of linking the piston to the crankshaft. It was originally designed to compete with the Otto engine, but without infringing on any of Otto's patents.
The clever arrangement of levers allows the Atkinson to cycle the piston through all four strokes in only one revolution of the main crankshaft, and allows the strokes to be different lengths -- the intake and exhaust strokes are longer than the compression and power strokes
Gnome
The Gnome was one of several rotary engines popular on fighter planes during World War I. In this type of engine, the crankshaft is mounted on the airplane, while the crankcase and cylinders rotate with the propeller.
The Gnome was unique in that the intake valves were located within the pistons. Otherwise, this engine used the familiar Otto four stroke cycle. At any given point, each of the cylinders is in a different phase of the cycle. In the following discussion, follow the master cylinder with the green connecting rod.
Trevithick's engine
Trevithick's engine, which worked a pump by way of a crossbeam, was most successful and was in use for a long time.
The steam (at 3-4 kg/cm²), was admitted in the cylinder only for 1/10 or 1/5 of the active stroke.
When the inlet valve is closed, the piston continues its active stroke by steam expansion.
When the piston reaches the bottom of the stroke an equilibrium valve opens to allow the steam to pass from above to below it.
The pressure above and below the piston is now equallized.
The upstroke is assisted by the crossbeam and the descent (by gravity) of the very heavy pump piston and rod.
When the piston has almost completed the upstroke, the equilibrium valve closes to make a steam cushion which reduces impact vibration.
The exhaust valve opens before the inlet valve opens.
The beam moves slightly under vacuum pressure alone and then accelerates greatly when the inlet valve opens.
In the cylinder below the piston, through a connection to the condenser, a partial vacuum is created. This assists the steam pressure above to drive the piston down, increasing the engine's efficiency.
Source : Internet