If we talk about motorcycles, many motorcycles were use 2 stroke engine in the past. But now, all motorcycle use 4 stroke engine. Why 2 stroke engine isn’t popular right now ?
In fact, it’s not. If we see the exhaust of 2 stroke engine, it has smoke. And this smoke, is kind of pollution. So, 2 stroke engine is no more used.
But what is the different between 2 stroke and 4 stroke engine ?
The source where the power of engine come from
Before we continue, there is one thing we need to understand. The engine produce rotational motion because there is combustion inside. These combustion, has expansion energy that pushes the piston. So the motion is created.
The point, the engine power is come from this combustion.
The 2 stroke engine, has 2 processes to do a combustion. While the 4 stroke engine, has 4 processes to do a combustion.
But what means processes Inside the engine ?
In simple terms, when piston move upward or downward, it is a stroke. It means, when piston move like this, it means the piston has done one process. And when the piston move back, it is one stroke. So overall, the piston has done two processes.
From this explanation, we know that the basic different between 2 stroke engine and 4 stroke engine, is on the number of processes.
4 Stroke Engine Processes
In 4 stroke engine, the processes consists of intake stroke, compression stroke, combustion stroke, and exhaust stroke. When the piston move down for the first time, it is intake stroke. Or, the air and fuel sucked inside the combustion chamber.
When piston move back upward, it Is compression stroke. This process use to press the air and fuel mixture. So that the temperature and pressure rise significantly.
When piston has reached the top position, spark plugs on. So the combustion occurs. The combustion pushes the piston. So the piston move down for the second time. It is combustion stroke. From this process, the energy is come from.
Then piston move upward. This time, the piston movement pushes the residual gas to the exhaust pipe. It is exhaust stroke. after the piston has done all process, it called a cycle.
After that, piston continue to move down to do the intake stroke for the next cycle.
Now, how about 2 stroke engine ?
In fact, 2 stroke engine has same processes with the 4 stroke engine. It consists of intake, compression, combustion, and exhaust stroke. But, in 2 stroke engine, 2 processes are completed by a piston movement.
So from this position, piston move upward. It make the crankshaft chamber expand. So that the air and fuel mixture sucked inside the crankshaft chamber. Then piston move down. Now, the crankshaft chamber is shrink, and intake port closed by pistob wall.
So that, the piston movement pushes the air fuel mixture into the combustion chamber via transfer port. So in this position, combustion chamber has filled with air fuel mixture.
Then piston move upward. It make the combustion chamber shrink. So that air fuel mixture is compressed. It called compression stroke. While in the bottom of piston, the crank chamber is expand. So that, the intake process is running.
In other word, in this stroke, there are two processes. Intake and compression.
When piston reached the top position, spark plug on. So that the combustion occurs. This combustion pushes the piston. So the piston move down. It is combustion process. In the bottom of piston, the crank chamber is shrink. So that the air fuel mixture is pushed into combustion chamber.
But, inside the combustion chamber there are residual gasses after combustion.
Evidently, when the piston move down, exhaust port is open. And it make the air fuel mixture from crank chamber, push the residual gas to flow out trough the exhaust port. It is exhaust processes. In other word, the second stroke consist of combustion and exhaust processes.
From that explanation, we know that the different between 2 stroke and 4 stroke engine is very basic.
But how about the smoke ? why 2 stroke engine has smoke ?
The smoke occurs because there are less oil burn. The oil come from crank chamber and come into combustion chamber with the air fuel mixture.
So the smoke in 2 stroke engine is normal for the smoke is not too concentrated. But, if 4 stroke engine smoky, it is not normal. Because 4 stroke engine doesn’t have way the oil to come into combustion chamber.
That’s the explanation about the different between 2 stroke and 4 stroke engine.