2 stroke vs 4 stroke engine | The Mechanical post

An engine is a mechanical power generator which converts heat energy produced by the combustion of fuel into mechanical work.

If you don't know what a 4 stroke and 2 stroke engines are, then do read in detail  about their construction and working:

What is 4 stroke engine ?

What is 2 stroke engine ?

A Four stroke engine is simply an engine which completes 4 strokes of the piston in 2 revolution of the crankshaft.A Two stroke engine is an engine which completes 2 stroke in one revolution of the crankshaft.So what's the difference? Well! let's check out 2 stroke vs 4 stroke :

Constructional difference between 4 stroke & 2 stroke engine:

  1. A four stroke engine has a oil ring around the piston, whereas 2 stroke engine doesn't have it.                                                                                                      
  2. A four stroke engine has a intake and exhaust valves while 2 stroke doesn't need it.                                                                                                                       
  3. A four stroke engine is complex as it has valve operating system which includes camshaft, cams, valves etc. The 2 stroke engine on the other end is simple in construction, without any inlet outlet valve.                                                       
  4. Two stroke engine has a smaller flywheel as compared to 4 stroke engine.                                   
  5. Two stroke engine is light in weight as compared to 4 stroke engine.                                         
  6. The crown of the piston is flat or dome shaped in a 4 stroke engine, while in a 2 stroke the crown of piston is provided with deflector for efficient scavenging.

                2 stroke engine

Working difference between 2 stroke engine & 4 stroke engine:

  • 2 stroke engine produce 1 power stroke in 1 revolution of crankshaft. Whereas, a 4 stroke engine produces 1 power stroke in every 2 revolution.  
  • Two stroke engine has less mileage as compared to 4 stroke.                         
  • Due to its construction 2 stroke engine produces more noise than 4 stroke engine.                                                                                                             
  • Four stroke engine's thermal efficiency is high as 4 stroke engine gives 1 power stroke every 2 revolution instead of one power stroke in 1 revolution as in the 2 stroke engine.

    Four stroke engine

Handling difference:

  1. Four stroke engine's fuel tank is required to be filled with petrol only. Whereas, 2 stroke engine requires oil and petrol mixture.                              
  2. Manufacturing cost of 2 stroke engine is less than as compared to 4 stroke engine.                                                                                                             
  3. Due to less parts, maintenance cost of 2 stroke engine is less, while the 4 stroke engine is comparatively expensive.

Advantages and disadvantages of 4 Stroke engine:

  • The cycle is complete in two revolution of crankshaft.
  • One power stroke is obtained in every two revolution of crankshaft.
  • Because of one power stroke for two revolutions, power produced for same  size engine is bulky.
  • The turning effort on crankshaft is not uniform so heavier flywheel is required.
  • 4 stroke engine contains valve mechanism.
  • Because of heavy weight and complication of valve mechanism, the              manufacturing cost of the engine increases.
  • Thermal efficiency is more.
  • Used where efficiency is important. E.g bus, truck, tractor, cars etc.

Advantages and disadvantages of 2 stroke engine:

  • The cycle is completed in one revolution of crankshaft.
  • One power stroke is obtained in every revolution of crankshaft.
  • Because of one power stroke for one revolution, power produced for same size engine is more. Theoretically, twice but in actual practice 1.5 times or for same power engine is light and compact.
  • The turning effort on the crankshaft is much more uniform so that lighter flywheel can be used. This reduces cost.
  • 2 stroke engine does not have valves but inlet and outlet ports are present.
  • Because of light weight and simplicity due to absence of valve, less initial cost.
  • Thermal efficiency is less.
  • Used where light and compact engine is required. E.g. scooters, lawn movers.

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