Advantages of Two Stroke Engine over Four Stroke Engine
The two-stroke engine gives one working stroke (Power Stroke) for each revolution of the crankshaft. Hence, theoretically the power developed by two-stroke engine is twice than that developed by four-stroke engine of same cylinder volume and same engine speed.
(a) The turning moment on the crankshaft is more in two-stroke engine due to one working stroke for each revolution of the crankshaft, and so a lighter flywheel is required in it.
(b) It is much cheaper to produce owing to the greater mechanical simplicity.
(c) It has high mechanical efficiency due to the absence of camshaft, cams and rockers etc. of the valves.
(d) It gives less torsional oscillation.
(e) It requires fewer spare parts due to its simple design.
Disadvantages of Two Stroke Engine over Four Stroke Engine
(a) More number of power strokes results in higher temperature of the engine and consequently lower thermal efficiency.
(b) The fuel consumption is high because the fresh charge is likely to be wasted by escaping through the exhaust port.
(c) The charge is diluted by the burnt gases due to incomplete scavenging.
(d) It consumes more lubricating oil.
(e) There is a greater wear and tear of moving parts.
(f) It needs a gas tight crankcase for drawing fresh charge.
(g) Difficult to get full charging and scavenging of cylinder due to short periods of port opening.
(h) It has low mean effective pressure.
(i) Two stroke engines have limited maximum speed and give irregular firing at light loads.