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Why 2-stroke Engines Are Used More Commonly Instead Of 4-stroke On Ships?



Both 2 stroke and 4 stroke engines are widely available in the market but for large ocean going merchant vessel, a 2 stroke engine is more commonly used as main engine and has much better market.



Even with wide variety of advantages that 4 stroke engine offers like compact size of plant, much more RPM or speed etc..and where as in case of  2 Stroke Engines they create a lot of noise and pollution but still ship engine uses 2 stroke engine for their propulsion.

Let us know the reason behind this:

1.)Fuel Selection:
The fuel prices have gone sky high and a large marine diesel engine may burn as much as three tonnes of oil per day !!! high grade fuel are more costly as compared to low grade fuel.A two stroke engine can burn low grade fuel oil and hence reduce running cost of the ship.


2.)High Torque:
2 stroke engine has more torque at low rpm than the 4 stroke. The ship needs the higher torque to keep a constant speed at the lower engine speed. So the ship can cruise at a constant speed without having to constantly adjust the engine speed.





3.)Power:
Two stroke engines are now large stroke engines that produces more power when compared to four stroke, per cycle by burning same amount of fuel from thermodynamic point of view..... Hence they have high power to weight ration as compare to 4 stroke engine.


4.)Reliability:
Two stroke engines have slow speed and so lesser wear and tear, economic from maintenanceand also more reliable in operation as compare to 4 stroke engine.


5.)Less Maintenance:
Two stroke engines are large sized, so better accessibility for maintenance and due to absence of valve mechanism,the maintenance requirement of two stroke engine is much lesser than 4 stroke engine.


6.)No reduction attachments:
As two stroke engines are low speed engine, and directly coupled to propeller so no need of reduction gear box or speed reduction arrangement as required for high speed four stroke engine.



7.)More Cargo: 
Ship can carry more weight and hence more cargo with 2 stroke engines because of high power to weight ratio.

8.)Efficiency: 
The thermal and engine efficiency of 2 stroke engine is much better than that of a 4 stroke engine.And produces more power compared to four stroke, per cycle by burning same amount of fuel.


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