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Since many farming and garden power tools now comes in both 4-stroke and 2-stroke models, there may be a confusion in making choices because you might be wondering which type of engine is better and why you should choose one type over the other.
This article helps you to make an informed choice by explaining the difference between the 2-stroke and the 4-stroke, how they work, and which is better depending on the buyer’s preference..
Before we continue, let’s explain the term‘Stroke. During an engine’s combustion cycle, the piston moves up and down within the cylinder. A stroke is when the piston moves from Top Dead Center(TDC) to Bottom Dead Center (BDC) or vice versa. The Top Dead Center refers to the position of the piston nearest to the valves, and Bottom Dead Center is its position furthest from them.
The number of cycles sometimes also referred to as strokes refers to the number of strokes the pistons in the engine need to make to produce power. In a 2-stroke engine, power is generated every two strokes while in a 4-stroke engine, four strokes are required.
The up and down movement of a piston within the cylinder results to air and gas being sucked into the piston. This process is called the Combustion cycle. A combustion revolution or combustion cycle is the complete process of gas and air being sucked into the piston, igniting it, and expelling the exhaust:
Therefore, the difference between a 2-stroke and a 4-stroke engine is how quickly this combustion cycle process occurs,i.e the number of times the piston moves up and down during each cycle.
In a 4-stroke engine, the piston completes 2-strokes during each revolution: one compression stroke and one exhaust stroke, each being followed by a return stroke. The spark plugs fire only once every other revolution, and power is produced every 4-strokes of the piston. These engines also do not require the combination of fuel and oil, as they have a separate compartment for the oil.
In a 2-stroke engine, the piston completes 1 stroke during each revolution: a compression stroke followed by the explosion of the compressed fuel. During the return stroke, the exhaust is let out and a fresh fuel mixture enters the cylinder. The spark plugs fire once every single revolution, and power is produced once every 2-strokes of the piston. In a 2-stroke engine, the oil and fuel are mixed together.
Benefits of a 2 stroke brushcutter engine over a 4 stroke brushcutter engine
Power: All other things being equal, that is,considering the size of the engine and the type of fuel being used, a 2 stroke engine will produce more raw power than its 4 stroke counterpart. This is because only two strokes are required to produce power, this means less work to do and greater power output. On the other hand, a 4 stroke engine has more work to do and so produce less power output.
However, 4 stroke engines are more powerful than comparable two stroke engines due to their greater efficiency. That said, the lighter weight two stroke engines can have a greater power-to-weight ratio which means you get more power per pound of engine weight with a two stroke engine. However, most of the power generated comes out as noise ,that is, it is used to expel the exhaust gases.
Cost:2 stroke engines are less expensive than their 4 stroke counterpart because they are a very simple engine with few moving parts
Weight:2 stroke engines weigh less than the 4 stroke engines because they are simpler in design
Easier to fix/repair: 2 stroke engines are easier to fix because they have a much simpler design.They have ports. 4 stroke engines have more parts, therefore they are more expensive and repairs cost more.
Benefits of a 4 stroke brushcutter engine over a 2 stroke brushcutter engine
Fuel efficiency: Though a 2 stroke engine produce more raw power, it burns up more fuel to do it.One of the biggest disadvantages of a two stroke engine, is the poorer fuel economy and high noise level from the exhaust. This is because about 25 to 30% of the explosion energy of the power stroke is used to expel the exhaust gases. This is not fuel-efficient at all. A well tuned muffler can be used to rectify this, however, it is difficult to use it in brush cutters because of their weight. On the other hand, in a 4 stroke engine, the process is much more efficient. This means they require less fuel since fuel is consumed once every 4 strokes..With a two-cycle, some of the fuel is wasted since it escapes during the combined intake and compression stroke. Conversely, with a four-cycle, there is no fuel wasted during intake of the air/fuel mixture since the fuel is drawn into a closed system
Pollution: Both engines uses gasoline and therefore causes pollution, however, a 2 stroke engine is less environmentally friendly because burnt oil is also released into the air with the exhaust.
Gas and oil mix: In this aspect, a 4-stroke engine is the undisputed champion. In a 4 stroke engine,the fuel and oil compartments are separate. Conversely, this is not so in a 2 stroke engine as it requires pre-mixing of fuel and oil, usually in a ratio of one part oil to 50 parts fuel (although this it can vary). This mixture ratio must be followed duly so as to avoid engine seizure
Sound: The 4-stroke engine is much quiet than a 2-stoke engine which is louder
Durability: A 4-stroke engine is more durable than the 2 stroke engine. This is because the latter is designed to run at a higher RPM and this makes them to wear out faster. These engines burn oil as well as fuel, hence creating a dirty combustion product in the chamber, thus leading to the wear and tear in the engine’s system. This reduces the overall life of the engine and makes a two-cycle generally less durable.However, 4 stroke engines run much cleaner and have a more effective dedicated lubrication system, this makes them have less wear and last longer.
Maintenance:Talking about maintenance, there is extra maintenance hassle for a 2 stroke engine because the fuel and oil is pre-mixed and should be used within 30 days of mixing. This is completely avoided in a 4 stroke engine.
As we have seen in the comparison above, there are a few significant differences between the two types of engines, although, in general terms, both are capable of getting the job done.
This means that there is no best option since the right choice depends on what you value and what you want to use it for. For example, If you want a simple but powerful machine and do not care about the noise or pollution, a 2-stroke is cool; If you are using a brush cutter for long periods of time, weight can be an important consideration;If you are less likely to be able to clean and maintain the dirtier burning two stroke engine, you might want to choose a 4 stroke model; also, if you prefer a more efficient machine, low noise , durability and one that doesn’t require a gas-oil m