Difference between two and four stroke engines
Two stroke engine vs four stroke engine:
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines (such as steam engines) burn a fuel to create heat which is then used to create motion. Majority of the world use vehicles and it is not a secret that vehicles have engine, which is considered to be the heart of the vehicle. These engines are classified as two stroke engines and four stroke engines. This article is aiming at providing a better knowledge to the reader on differences between two stroke engine and four stroke engines, of which most of us are not aware.
What is a two stroke engine?
A two-stroke in its purest form is extremely simple in construction and operation, as it only has three primary moving parts (the piston, connecting rod, and crankshaft). A two-stroke, two-cycle, or 2-cycle engine is a type of internal combustion engine which completes a power cycle in only one crankshaft revolution and with two strokes, or up and down movements, of the piston in comparison to a “four-stroke engine”, which uses four strokes to do so. They are commonly found in lower-power applications. Since the two stroke engine fires on every revolution of the crankshaft, a two stroke engine is usually more powerful than a four stroke engine of equivalent size. Two-stroke engines often provide high power-to-weight ratio, usually in a narrow range of rotational speeds called the “power band”, and, compared to 4-stroke engines, have a greatly reduced number of moving parts. They fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost. This, coupled with their lighter, simpler construction, makes the two stroke engine popular in chainsaws, line trimmers, outboard motors, snowmobiles, jet-skis, light motorcycles, and model airplanes. The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging cylinder. Two-stroke engines do not have valves, simplifying their construction. Two-stroke engines are lighter and cost less to manufacture and also they have the potential for about twice the power in the same size because there are twice as many power strokes per revolution. Unfortunately, most two stroke engines are inefficient and are terrible polluters due to the amount of unspent fuel that escapes through the exhaust port. Two-stroke engines don’t live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.
What is a four stroke engine?
Most cars use four-stroke engines. A four-stroke engine, also known as four-cycle, is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine’s crankshaft, and one single thermodynamic cycle. Four-stroke internal combustion engines transform thermal energy to mechanical energy. A spark causes an air-fuel mixture to ignite, forming hot gases. The hot gases expand and force the piston to move. The piston’s motion turns a crankshaft. The motion of the crankshaft is transferred to the wheels of the car. A 4 stroke engine has 1 compression stroke and 1 exhaust stoke. Each is followed by a return stroke. The compression stroke compresses the fuel air mixture prior to the gas explosion. The exhaust stroke simply pushes the burnt gases out the exhaust. A 4 stroke engine usually has a distributor that supplies a spark to the cylinder only when its piston is near TDC (top dead center) on the fuel compression stroke, i.e. one spark every two turns of the crank shaft. Some 4 stroke engines do away with the distributor and make sparks every turn of the crank. This means a spark happens in a cylinder that just has burnt gasses in it which just means the sparkplug wears out faster. As mentioned above, the four cycles of the four stroke engine are called intake stroke, compression stroke, power stroke and exhaust stroke. There are two common types of four-stroke engines. They are closely related to each other, but have major differences in design and behaviour. The earliest of these to be developed is the Otto cycle engine developed in 1876 by Nikolaus August Otto in Cologne, Germany, after the operation principle described by Alphonse Beau de Rochas in 1861. This engine is most often referred to as a petrol engine or gasoline engine, after the fuel that powers it. The second type of four-stroke engine is the Diesel engine developed in 1893 by Rudolph Diesel, also of Germany. Diesel created his engine to maximize efficiency, which the Otto engine lacked.
What is the difference between four stroke engines and two stroke engines?
Above all, four stroke engines have more parts than the two stroke engines. When it comes to the number of strokes, as suggested by the name, two stroke engines have only two strokes per cycle; a stroke during intake and compression, and the other during combustion and exhaust. When it comes to the four stroke engine, it has four strokes per cycle and those are intake, compression, combustion and exhaust. Two stroke engine fires 1 time in each revolution whereas a four stroke fires 1 time in two revolutions. Two strokes engine is simpler and lighter, but less versatile. In two stroke engine, it has 2 ports for the inlet and the exhaust purposes. That means it has no valves so that it has a simple structure than a four stroke engine. The function of the valves is done by the piston and those 2 ports it has valves for intake and exhaust processes. Since this has valves and dedicated intake, compression, power and exhaust strokes, the fuel consumption is getting better. In four-stroke engine, it produces more torque at low RPM. Another difference noticed when handling an engine is that a four stroke engine weighs more than the two stroke engine. Two stroke engines have combustion event in each and every resolution. Due to this reason it has a significant power boost. Therefore, considering these two factors it is apparent that it has a higher power-to-weight ratio. However, four-stroke engine has a fine lubricating system. Therefore, they last longer than two stroke engines. In addition, when using gas, four-stroke engine is more efficient. Therefore, pollution occurs in a small amount. While four stroke engines are more expensive than two strike engines, two stroke has a shorter engine than the four stroke. While two stroke engines consume more fuel capacity than a four stroke, four stroke engines have high compression ratio and high thermal efficiency. Four stroke engines are more fuel efficient and environmentally friendly when compared to four stroke engines.
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