Now, there are numerous types of engines available for autos. However, the two most common engine types are 2-stroke and 4-stroke. Also, when the piston moves from the top dead center (TDC) to the bottom dead center (BDC), or vice versa, to generate power, this movement is known as a stroke. A stroke is a primary action in an engine that starts the combustion process.
Now, let’s understand the main differences between 2 strokes and 4 strokes.
2 Stroke vs 4 Stroke
The fundamental method of operation is the primary distinction between 2 and 4-stroke engines. Flywheel weight is a requirement for 4-stroke engines while flywheel weight is a requirement for 2-stroke engines. Both engines can be distinguished based on their intended purpose, with 2-stroke engines being found in scooters and mopeds and 4-stroke engines in large or off-road vehicles.
Difference Between 2 Stroke and 4 Stroke in Tabular Form
|Parameters of Comparison
|No. of crankshaft revolutions
|High torque generation.
|Low torque generation.
|Fuel’s outlet and inlet
|Uses ports here.
|Uses valves here.
|Less thermal efficiency.
|High thermal efficiency.
|It is cheaper.
|It is expensive.
What is 2 Stroke?
Now, a two-stroke (or two-stroke cycle) engine is a kind of internal combustion engine that performs two piston strokes (up and down movements) throughout a power cycle, which would be finished in one crankshaft revolution. In a four-stroke engine, a power cycle lasts for two crankshaft revolutions and involves four piston strokes.
Now, in a two-stroke engine, the intakes and exhaust (or scavenging) activities happen simultaneously at the part of the combustion stroke and the start of the compression stroke.
Moreover, due to the power being accessible in a constrained range of rotational speeds known as the power band, two-stroke engines frequently have a high wattage ratio. Compared to the four engines, the engine has fewer moving parts.
Dugald Clerk, a Scottish engineer, is credited with developing the first commercial two-stroke engine with cylinder compression; his design was patented in 1881. His, however, had a separate charge cylinder, unlike the majority of succeeding two-stroke engines. The Englishman Joseph Day is generally recognized as the inventor of the crankcase-scavenged engine, which uses the space below the piston as a charging pump. German inventor Karl Benz created a two-stroke gas engine on December 31, 1879, for which he was granted a patent in Germany in 1880. Alfred Angas Scott, a Yorkshireman who began making twin-cylinder water-cooled motorcycles in 1908, is credited with developing the first fully practical two-stroke engine.
Chainsaws and motorbikes are two-stroke gas engines with electrical spark ignition and are especially helpful in light or portable applications. The cycle is appropriate for diesel compression ignition working in large, weight-insensitive applications, such as ship engines, railroad locomotives, and electricity production because it has the potential for high thermodynamic efficiency. When compared to a four-stroke engine, a two-stroke engine's exhaust gases carry less heat to the air conditioning system, which frees up more power for the piston and, if one is present, a turbocharger.
Crankcase-compression In a total-loss system, two-stroke engines, such as typical small gasoline engines, are lubricated by a petrol mixture. Their gasoline is pre-mixed with oil at a fuel-to-oil ratio of about 32:1. This oil then emits pollutants, either as droplets in the exhaust or as it burns in the engine, historically producing more hydrocarbons in the exhaust than four-stroke engines with equivalent power output. Some two-stroke designs additionally permit a small number of unburned gasoline vapors to exit in the exhaust stream during the combined opening time of the intake and exhaust ports. NOx emissions may also be produced by the small, air-cooled engines' high combustion temperatures.
However, a modern two-stroke engine can achieve higher thermodynamic efficiency and emit air pollution that is comparable to that of a four-stroke when equipped with continuous fuel injection and a sump-based lubrication system.
When mechanical simplicity, minimal weight, and a high power-to-weight ratio are design considerations, two-stroke gasoline engines are favored. They may run in any orientation because the oil reservoir is not gravity-dependent by combining oil and gasoline.
Two-stroke engines have formerly been utilised by a number of well-known automakers, including the German DKW, Auto-Union, VEB Sachsenring Automobilwerke Zwickau, VEB Automobilwerk Eisenach, and VEB Fahrzeug- und Jagdwaffenwerk „Ernst Thälmann. In the 1970s, Japanese automakers Suzuki and Subaru followed suit. Due to more rigorous air pollution regulations, two-stroke car production was put to a halt in the West in the 1980s. The Trabant and Wartburg in East Germany remained in use until about 1991 in the Eastern Bloc nations.
Outboard engines, small on- and off-road motorbikes, mopeds, scooters, tuk-tuks, recreational vehicles, go-karts, ultralight, and model airplanes are just a few minor propulsion devices that still use two-stroke engines. Pollution rules, particularly in industrialized nations, have caused the use of many of these technologies to be phased out. For instance, Honda abandoned road-going versions far earlier and stopped marketing two-stroke off-road motorbikes in the United States in 2007.
Two-stroke engines, which have a high power-to-weight ratio and can be used in any direction, are frequently seen in handheld outdoor power equipment like leaf blowers, chainsaws, and string trimmers.
Several trucks and pieces of heavy equipment, as well as big industrial and maritime applications, use two-stroke diesel engines.
The technical intricacies of many two-stroke engines vary depending on the kind, even though the fundamentals stay the same. The design types differ depending on how the charge is introduced into the cylinder, how the cylinder is scavenged (burnt exhaust is replaced with the fresh mixture), and how the cylinder is exhausted.
What is a 4-Stroke?
An internal combustion (IC) engine is referred to as having four strokes (also known as four cycles) when the piston is rotating the crankshaft. A piston's whole travel in either direction along the cylinder is referred to as a stroke. The four distinct strokes are known as:
- Intake: Suction and induction are other terms for intake. The piston's current stroke has a top dead center (T.D.C.) and a bottom dead center (B.D.C.) (B.D.C.). The intake valve must be open throughout this stroke as the piston forces fuel and air into the cylinder by creating vacuum pressure inside the cylinder as it descends. Air is drawn in by the downward action against the piston, which causes it to descend.
- Compression: Known as the compression stroke, it starts at B.D.C., or right after the suction stroke, and finishes at T.D.C. The piston compresses the air-fuel mixture during this stroke to get it ready for ignition during the power stroke (below). During this phase, the intake and exhaust valves are both shut.
- Combustion: Power or ignition are other names for combustion. The four-stroke cycle's second revolution has just begun. The crankshaft has turned a full 360 degrees at this point. The compressed air-fuel combination is ignited by a spark plug in a gasoline engine or by heat produced by high compression in a diesel engine while the piston is at TDC (the end of the compression stroke), forcing the piston back to BDC. By turning the crankshaft during this stroke, the engine generates mechanical work.
- Exhaust: Also known as an exit, and exhaust. The piston once more moves from BDC to TDC during the exhaust stroke when the exhaust valve is open. Through the exhaust valve, the used air-fuel mixture is released in this motion.
It may be simpler to remember if you refer to these four strokes as "suck, squeeze, bang, and blast," respectively. The most popular internal combustion engine type for motorized land transportation is the four-stroke engine, which is used in cars, trucks, diesel trains, light aircraft, and motorbikes. The two-stroke cycle is the main alternative design.
Like all combustion engines, four-stroke engines emit considerable amounts of greenhouse gases as well as other types of air pollution in their exhaust emissions. In some places, the use of four-stroke engines in automobiles and other forms of transportation is slated for a phase-out beginning in 2022, while other significant jurisdictions are contemplating ideas along the same lines.
The actual four-stroke and two-stroke cycles' thermodynamic analysis is a difficult task. However, if air standard assumptions are used, the analysis can be greatly simplified. The end product is the Otto cycle, which closely reflects the real operating circumstances.
Now, an electric spark is produced to ignite the mixture during normal engine operation as the air/fuel combination is squeezed. This occurs close to TDC at low rpm (Top Dead Centre). Also, the speed of the flame front does not change as engine rpm increases, so the spark point is advanced earlier in the cycle to give the charge more time to burn before the power stroke starts. So, this benefit is demonstrated by the different Otto engine designs; the atmospheric (non-compression) engine operates at a 12 percent efficiency while the compressed-charge engine operates at a 30 percent efficiency.
Compressed charge engines have the issue that pre-ignition can be brought on by the compressed charge's temperature rise. This can harm the engine if it happens at the incorrect time and with too much vigor. The flash points of various petroleum fractions vary greatly (the temperatures at which the fuel may self-ignite). The design of the engine and fuel must take this into account.
The chemical makeup of the fuel regulates the compressed fuel mixture's propensity to ignite early. To meet different engine performance levels, different gasoline grades exist. The fuel is changed to adjust the temperature at which it self-ignites. There are various methods for doing this. Pre-ignition is significantly more likely to happen as a result of greater compression ratio engines because the fuel mixture is pushed to a higher temperature before intentional ignition. Fuels like gasoline may be evaporated more efficiently at a greater temperature, which boosts the compression engine's effectiveness. Additionally, higher compression ratios increase the piston's power-producing range of motion (which is called the expansion ratio).
An indicator of a fuel's resistance to self-ignition is its octane rating. A fuel with a higher numerical octane rating enables a higher compression ratio, which pulls more energy from the fuel and more successfully transforms that energy into usable work while also reducing pre-ignition damage to the engine. Additionally, high-octane fuel is more expensive.
Now, Gasoline direct injection, or GDI, is a common feature of contemporary four-stroke engines. Then an engine that uses direct injection of gasoline has an injector nozzle that extends into the combustion chamber. So, the compression stroke, when the piston is at the top, is when the direct fuel injector injects gasoline into the cylinder at very high pressure.
Also, by definition, pre-ignition is not a problem for diesel engines. They are worried about whether or not combustion can occur. The Cetane rating is a measure of how likely diesel fuel is to catch fire. Diesel fuels have low volatility, which makes them difficult to start when cold. The most popular method for starting a cold Diesel engine is the use of a glow plug.
Main Differences Between 2 Stroke and 4 Stroke In Points
- Now, the movement of the crankshaft and piston is the primary distinction between 2-stroke and 4-stroke engines in terms of how they operate.
- Along with their purposes, their performance, maintenance costs, and efficiency are also key factors in determining how they differ.
- 4-strokeke engines provide a high power output and are less loud. In comparison to 2-stroke engines, it also has lower maintenance costs.
- Both engines have several applications, which is another difference. While 4-stroke engines are employed in big and offload equipment and engines, 2-stroke engines are used in tiny and light machinery.
- Compared to 2-stroke engines, which are tiny and take up less space, 4-stroke engines take up a lot of room and are difficult to manage. 2-stroke engines are simple for one to handle.
Technically speaking, both 2 and 4-stroke engines are necessary, and they essentially have different uses in various contexts. However, if we look at performance, 4-stroke engines are preferable because they require less upkeep and produce more power. In contrast, a two-stroke engine is less expensive, takes up less room, and is simple to use and handle. As a result, each engine has various advantages and disadvantages related to its performance and design.
- Four-stroke engine. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Four-stroke_engine
- Two-stroke engine. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Two-stroke_engine