Internal Combustion Piston Engines

Exhaust stroke
Again the momentum of flywheel moves the piston up from BDC to TDC thereby driving the exhaust gases outside through the exhaust valve.
Key points:
Intake valve – CLOSED
Exhaust valve – OPEN
Crankshaft rotation – 180°(total = 720°)

Two-stroke vs Four-stroke
Two-stroke
Lighter;
More efficient;
Ability to use lower-grade fuel;
More cost-efficient;
Higher power-to-weight ratio (more power for less weight);
Ideal for ships, motorcycles and lawn mowers.
Four-stroke
More possible maneuverability;
Require less lubrication;
Larger thermal efficiency;
Ideal for automobiles like cars and trucks.

Advantages
Size of engine is very less compared to external combustion engines;
Power-to-weight ratio is high;
Very suitable for small power requirement applications;
Usually more portable than their counterpart external combustion engines;
Safer to operate;
Starting time is very short;
High efficiency than external combustion engine;
No chances of leakage of working fluids;
Requires less maintenance;
Lubricant consumption is less as compared to external combustion engines.
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