A two-stroke engine is an internal combustion engine. This type of engine is called a “Two-stroke engine” because there are two strokes: a compression stroke and a combustion stroke. Two-stroke engine was first designed in the year 1878 by Sir Dugald Clerk, a Scottish engineer. But the two-stroke engine, as it is known today, was designed by Joseph Day. It was very popular during the 20th century.
In a two stroke engine, the mixture of fuel and air is drawn into the crankcase from the carburetor by the vacuum created during the upward stroke of the piston. This mixture is then compressed inside the cylinder. The spark plug ignites this mixture of fuel and air. This process drives the piston down. While doing so, the piston compresses the mixture of air and fuel in the crank case. This downward movement of the piston also uncovers the exhaust port. Exhaust gases move out of this port.
The piston performs many functions in a two stroke engine. It compresses the mixture of fuel and air and captures the energy released due to their ignition. It facilitates appropriate intake of the mixture of air and fuel from the carburetor. It creates pressure in the crank case, forcing the mixture of air and fuel to the combustion chamber. It also performs the function of a valve, by covering and uncovering the intake and exhaust ports.
Two-stroke engines are used to run lightweight devices like dirt bikes, model airplanes, lawn mowers, mopeds, chain saws, jet skis and leaf blowers. The number of moving parts in a two stroke engine is lesser than that in a four stroke engine. These engines do not require valves. Because of this they weigh lesser than four stroke engines. Two stroke engines have an excellent power to weight ratio.
In a two stroke engine, the spark plug ignites once on each revolution of the crankshaft. But in case of a four stroke engine, it ignites once every two revolutions. Four stroke engines do not work properly if they are not upright. But two-stroke engines work in any orientation. Two-stroke engines are more efficient and less expensive than four-stroke engines.
Two-stroke engines have their own disadvantages. They are less durable than four stroke engines. They are not environment friendly. Two stroke engines pollute the air more than four stroke engines. Vehicles with four-stroke engines are more fuel efficient than those with two-stroke engines.