Comparison between Four Stroke and Two Stroke Engines

Here is a comparison between four Stroke Engine and two Stroke Engines in tabular form.

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
Torque Uniform Non-uniform
Flexibility for operations Low High
Scavenging* Poor Good
Lubrication Requirement High Low
Cooling Requirement High Low
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 4 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 4 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.”

*

Scavenging

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.

Spark Ignition

spark-ignition engine is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug.

compression-ignition

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.

Enjoyed reading, also read SI and CI Engines.

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