Difference between 4 stroke engine & 2 stroke engine
Serial No.
|
4
Stroke Engine
|
2
Stroke Engine
|
1
|
It has one power stroke for every two revolution of crankshaft.
|
It has one power stroke for every revolution of crankshaft.
|
2
|
Heavy flywheel is required and engine is balanced.
|
Lighter flywheel is required and engine is unbalanced.
|
3
|
Engine is heavy.
|
Engine is lighter.
|
4
|
Engine design is complicated due to valve mechanism.
|
Engine design is safe due to absence of valve mechanism.
|
5
|
Less mechanical efficiency due to more friction in parts.
|
More mechanical efficiency.
|
6
|
Engine is usually water cooled.
|
Engine is air cooled or water cooled.
|
7
|
Less fuel consumption and complete burning of fuel.
|
More fuel consumption and air is mixed with burnt gases.
|
8
|
Engine requires more space.
|
Engine requires less space.
|
9
|
Engine consist of inlet and exhaust valves.
|
Engine consist of inlet ports and exhaust ports or valves.
|
10
|
Thermal efficiency is more.
|
Thermal efficiency is less.
|
2 Stroke timing diagram
Operation of a 2-stroke diesel engine
 |
| Pic: 2 Stroke timing diagram |
Numbers
|
Actions
|
0
|
Scavenge ports are open.
|
0-1
|
Air is sucked in, which pushes out the residual exhaust gases.
|
1
|
Piston is at BDC.
|
1-2
|
Completion of scavenge process and filling of fresh air for
combustion.
|
2
|
Scavenge ports are closed.
|
2-3
|
Post scavenging takes place.
|
3
|
Exhaust valves closes.
|
3-4
|
Compression of air.
|
4
|
Fuel injection commences.
|
5
|
Fuel injection commences, near TDC
|
6
|
Fuel injection and combustion completion.
|
6-7
|
Expansion of the heat energy from combustion, being converted into
work energy to push the piston downward.
|
7
|
Exhaust valve opens.
|
7-0
|
Blowdown of exhaust gases seen as a sudden rapid pressure drop on the
P.V.diagram.
|
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