You may have operated a lawnmower, jet-ski, scooter or a much bigger engine like that of a truck. These engines are classified into two stroke or four stroke types. The make-up of an engine can sometimes help you determine which machine suits your needs. In order to understand the advantages and disadvantages of each of these engines, you need to know how they work.
A 2 stroke engine’s piston makes one stroke in each direction to operate a given machine.
- A compression stroke compresses the fuel which then explodes.
- The return stroke, called the power stroke, is driven by the exploded fuel. It moves the crank case, releases exhaust gases, and lets in new fuel and air for the next stroke.
A 4 stroke engine makes four strokes to drive the engine.
- The compression stroke compresses air and fuel.
- The power stroke. The compressed air is ignited, driving down the piston which turns the crankshaft in the process as well as providing enough energy to drive the other three strokes.
- Exhaust stroke. As the piston moves up, it releases exhaust gases through the exhaust valve.
- Intake stroke lets in a new supply of fuel and air for the first stroke.
|2 Stroke Engine||4 Stroke Engine|
|Its piston makes two strokes in the engine||Its piston makes four strokes in the engine|
|Less efficient, hence environmentally unfriendly||Efficient, hence environmentally friendly|
|Relatively cheaper as they don’t have valves||Relatively expensive because of the complexity of incorporating valves|
|Produce high power for a relatively short period||Produce low power for a long period|
|The extra oil required to mix with fuel makes them expensive to maintain||Doesn’t require oil in the fuel|
The differences can be seen in the number of strokes each piston takes, and their structure.
- The piston in a 4 stroke engine makes four strokes that drive the crankshaft. Due to their weight and the number of firings that drive the crankshaft, these engines can only produce low but sustained amounts of energy that is ideal for use in things like trucks that need to go long distances without stopping. By contrast, the 2 stroke engine is capable of producing quick and sudden bursts of power that are not sustained for a long period of time. This makes it ideal for use in chainsaws and jet skis that stop from time to time.
- A 2 stroke engine is easier to construct since it has no valves. This makes it lighter and cheap to manufacture. A 4 stroke engine requires elaborate valves to operate effectively, making it heavy and expensive to assemble.
- A 2 stroke engine requires no oil sump. The oil mixed with the gas does not adequately lubricate the engine. It is therefore not likely to last long. The cost of the short life and that of mixing oil with its fuel makes them expensive in the long run. A 4 stroke engine does not require oil mixed with the gas and so it is cheap to run.
- 2 stroke engines are not so efficient in burning fuel. For this reason, they pollute the environment more than 4 stroke engines.
Here is a video that highlights the major differences between a two stroke and a four stroke engine, with pros and cons of each: