2 Stroke |
4 stroke |
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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 |