Difference between two and four stock engine?

Two Stroke Engine: In a two stroke engine, there is a power stroke in every rotation of the crank shaft since the thermodynamic cycle is completed in two strokes of the piston. Because of the above reason, the turning moment is more uniform. So a lighter fly wheel is used in the case of a two stroke engine. Because of the ability to obtain a power stroke in each rotation of the crank shaft, the power produced is twice compared to four stroke engine if the size is same. There are no valve system provided for two stroke engine, This made the working and design simpler. Due to the absence of valve system and light weight, the initial production cost of two strike engine is low. In the case of two stroke engine, the volumetric efficiency is less due to lesser time for induction. Here, thermal efficiency is lower and part load efficiency is poorer. There is chance for incomplete burning due to short circuiting and so causes environmental pollution. These internal combustion engines are used where low cost, compactness and light weight are important considerations. Examples are in scooters, motor cycles, etc.. Four Stroke Engine: In a four stroke engine, there is only a power stroke in every two rotations of the crank shaft since the thermodynamic cycle is completed in four strokes of the piston. Because of the above reason, the turning moment is less uniform. So a heavier fly wheel is used in the case of a four stroke engine. Because of the production of only a power stroke in each two rotations of the crank shaft, the power produced is half compared to two stroke engine if the size is same. There is valve system provided for four stroke engine. This made the working and design of this engine complex. Due to the presence of valve system and increased weight, the initial production cost of four strike engines is high. In the case of four stroke engine, the volumetric efficiency is high due to larger time for induction. Here, thermal efficiency is higher and part load efficiency is better. There is less chance for incomplete burning and so less chances for environmental pollution. These engines are used where efficiency is important. Examples are in cars, buses, trucks, etc.. read less

A two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle. read less

At first Four stroke engines were developed where Power stroke is generated for every 4 revolutions of a crank shaft later the need for generating more power at minimum number of strokes, two strokes engines were developed. Now lets see the major differences 1.In a two stroke Engine Power is generated for every 2 revolutions of crank shaft, where as in a four stroke engine Power stroke is generated for every four revolutions of a crank shaft. 2. Two stroke engines have ports for inlet of charge & exhaust, where as four stroke engines have inlet and exhaust valves. 3. Two stroke engines have much better scavenging efficiency than four stroke engines. 4. Two stroke Engine is very light and compact because of the absence of valve mechanism and can be used for hand chain saws. Four stoke engines are comparably compact when compared with 2 stroke engines. 5. Typically two stroke engines are used in motor cycles were as four store engines are used in Bikes, Cars and heavy Vehicles. read less