2 stroke scooters are almost a history. These days almost all vehicles (scooters or bikes) are equipped with 4-stroke engines. This is because 2-stroke engines deliver low fuel efficiency eventually low mileage and also greater levels of pollution. On the contrary, 4-stroke engine vehicle delivers enhanced performance, fuel efficiency and greater mileage.
A four-stroke engine is characterized by a/an
Intake stroke
Compression stroke
Combustion stroke
Exhaust stroke
It is these characteristics that aid in transforming fuel into motion. One-stroke cycle implies single complete down or up movement of the piston. In a 4-stroke engine there exists 2 complete up and then 2 complete down movement of the piston for the engine combustion.
The engine cycle starts with the intake stroke. In the intake stroke, piston moves down and the intake valve opens up. Fuel mixed with air is taken in the cylinder and in the combustion chamber. Then, in the compression stage, the fuel-air mixture is compressed as the piston moves back and then up. The correct mixture of air and fuel is ascertained by carburetor. In this stage of compression there is no heat transfer in the fuel-air mixture. With the decreased volume of the mixture, gas pressure increases in the combustion chamber. Next, as the piston reaches the top, the spark plug ignites the gasoline in combustion stroke finally bringing the piston down. As the piston hits bottom, the exhaust valve gets opened and the pressure of burning fuel pushes the combustible products out of the cylinder through exhaust valves.
How does the piston move up and down?
By the crankshaft throw, the piston basically moves up and down. It is the revolution of the crankshaft that provides with two strokes to the piston. Thus in a four-stroke engine for the piston to move complete 4 strokes, the crankshaft need to turn twice. Again one must know that the degree of crankshaft travel is not same for all the four strokes of the piston.