|Description||Two Stroke Engine||Four Stroke engines|
|Output/Revolution of crank shaft||High||Low|
|Mechanical Simplicity||High, since port are used for fuel intake||Low, since valves are used for fuel intake|
|Cost||Comparatively Cheap||Comparatively High|
|Flexibility for operations||Low||High|
|Spark Ignition-Uses||For small engines||For big engines|
|Spark Ignition* -Charge loss||Charge loss during scavenging||No such loss|
|Compression Ignition* -Fuel loss||No fuel loss||No fuel loss|
|Compression Ignition-Power output||High||Low|
Four Stroke Engine
The name itself gives us an idea – it is an Internal Combustion Engine where the piston completes four strokes while turning the crankshaft twice.
A stroke refers to the piston travelling full in either of the direction.
A cycle gets completed when all the four strokes get completed.
The four stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it is also known as the Otto cycle.
Two Stroke Engine
A two-stroke engine performs all the same steps as a four stroke engine, but in just two piston strokes.
The simplest two-stroke engines do this by using the crankcase and the underside of the moving piston as a fresh charge pump.
Such engines carry the official name “crankcase-scavenged two-strokes.”
In automotive usage, scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air or fuel/air mixture for the next cycle.
A compression-ignition engines, typically diesel engines, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.