MEO FUNCTION IV

What are the differences between 2 ST & 4 ST diesel engine?

 
  2 Stroke
4 stroke
 
1 It has one power stroke for each revolution of the crankshaft. It has one power stroke for every two revolutions of the crankshaft.
2 Lighter flywheel is required and engine runs balanced because turning moment is more even due to one power stroke for each revolution of the crankshaft. Heavy flywheel is required and engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft.
3 It is of crosshead type i.e. piston rod connected to the crosshead bearing both reciprocate along the axis of the piston. It is of trunk type i.e. the skirt is connected to connecting rod by means of a gudgeon pin and bearing.
4 The crosshead slippers transmit the connecting rod angularity thrust to the crosshead guides. Trunk or extension piece or extended skirt takes the connecting rod angularity thrust and transmits it to the side of the cylinder liner.
5 More height for same power and speed. Less height for same power and speed.
6 More head room. Headroom is limited.
7 Power/ weight ratio is high. Power/ weight ratio is low.
8 These are used mostly in slow speed engine. These  are mostly used in medium/ high speed engine.
9 They have long stroke. They have short stroke. (1-1.5)
10 These are used for propulsion purpose. These are used mainly for power generation.
11 It has compression type piston rings. It has compression as well as oil scrapper rings.
12 Directly engine shaft coupled to propeller giving good efficiency as propeller is larger at a very slow speed Gear box is used for coupling to propeller (Reason: if directly coupled, prop@ 800 rpm, cavitation occurs, efficiency drops)
13 Can  burn low Grade fuel Requires better grade fuel (Low Ignition lack fuel)
14 Low Compression Ratio High Compression Ratio (1:16)
15 Requires warming of engine Doesnot require warming of Engine “Life Boat ratio 1:18/20”
16 More Pollution Less pollution
17 Thermal efficiency is not better Thermal efficiency is better

About the author

Anand Gautam

Anand Gautam is a marine engineer, Graduated from M.E.R.I. Mumbai. He likes to sail onboard ship and is one who is passionate about his job. He loves to share his knowledge, information, and ideas to everyone in a simplified way just for his satisfaction.

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