An engine is a machine that transforms the fuel’s thermal energy into mechanical energy. Fuel is burnt in the combustion chamber, then used with a piston, connecting rod and crankshaft to generate power.
Then it can be classified according to the design, fuel, stroke, cylinder number and position. In an internal combustion engine, stroke is defined as how the cylinder piston moves up and down.
The cycle begins with the intake stroke, during which a new air-fuel mixture enters the engine cylinder as the piston moves downwards. Stroke is the length of travel the piston has travelled, which means it is a factor used to calculate the engine’s displacement. We will also discuss the working, the application and the difference between Two and Four-Stroke Engines.
What is a Two-Stroke Engine?
A two-stroke engine is an engine that finishes a power cycle with two strokes of the piston during just one crankshaft revolution. In a two-stroke engine, two processes occur simultaneously in every stroke, i.e. suction and compression in the first, power and exhaust in the second.
A two-stroke engine consists of a few mechanical parts, including Piston, Crankshaft, Connecting Rod, Flywheel, Spark Plug, Counter Weight, Inlet and Outlet Ports.
For a 2-stroke engine to finish the full combustion cycle, which consists of five procedures (intake, compression, ignition, combustion and exhaust), the cycle requires two piston strokes.
A two-stroke engine comprises two procedures:
- Compression stroke: When the inlet port is opened, the given air-fuel mix enters the chamber, lifting the piston and compressing this very mixture. A spark plug fires the compressed fuel and starts the work process.
- Power stroke: The heated gas exerts a high force on the piston; the piston moves downwards (expansion), where the residual heat is dissipated.
Applications of a Two-Stroke Engine
- Two-stroke engines are preferred when mechanical simplicity, lightweight, and high power to weight ratio are prioritised in the design.
- They are oiled by the traditional process of combining oil with fuel. They can be machined in any orientation as they do not have gravity deposits, making them desirable for hand tools such as chainsaws.
- Two-stroke engines are found in small drive applications such as motorcycles, mopeds, and dirt bikes.
- Due to their layout and absence of an oil sump, two-stroke engines are also simpler to turn on in cold weather, making them suitable for usage in snowmobiles.
What is a Four Stroke Engine?
A four-stroke engine is an internal combustion engine in which the piston makes four separate strokes while rotating the crankshaft.
The four-stroke engine has 4 steps which can be defined below-
Step 1: Intake Stroke
It attracts an air-gas aggregate into the combustion chamber. The piston plunges withinside the cylinder bore to drain the combustion chamber. When the inlet valve opens, atmospheric strain pushes the air-gas rate into the evacuated chamber.
Step 2: Combustion Stroke
The cylinder is full of the maximum combination, and the consumption valve seals the combination and the piston shifts upward.
The compression takes place among the piston and the cylinder head.
Step 3: Power Stroke
After completing the compression stroke, the spark torches the air-gas combination and pushes the piston to backtrack, the cylinder bore generates torque inside the crankshaft.
The strain at the piston determines the quantity of torque produced.
Step 4: Exhaust Stroke
The exhaust stroke takes place whilst residual gases released from the combustion chamber are freed into the atmosphere.
The exhaust stroke is the completing stroke and takes place whilst the exhaust valve is open and the consumption valve is closed. Piston motion frees exhaust gases into the atmosphere.
Applications of a Four-Stroke Engine
- The four-stroke engine is the most widely used, particularly the one that mainly uses gasoline as fuel.
- Vehicles like cars, vans and a few bikes have four-stroke engines.
- Some other collections are small propeller aircraft, formula one, small motor-powered boats, auto-rickshaw, water spray systems, etc., all of them having a four-stroke engine.
- Four-stroke engines are useful for go-karts, lawnmowers, and dirt bikes. They are also useful in the regular internal combustion engine of our vehicle.
Differences between a Two-Stroke Engine and a Four-Stroke Engine
- A two-stroke engine has one crankshaft revolution during one power stroke. The four-stroke engine has two crankshaft revolutions during one working stroke.
- Two-stroke engines use the connector for the fuel inlet and outlet, while the four-stroke engine uses valves for the fuel inlet and outlet.
- Two-stroke engines lead to lower thermal efficiency, and four-stroke engines lead to higher thermal efficiency.
- A four-stroke engine requires less lubricating oil than a two-stroke engine. A two-stroke engine plus lubricating oil, as part of the oil, is burned with the fuel.
- Two-stroke engines are cheaper and easier to manufacture, while four-stroke engines are expensive and difficult to manufacture due to lubrication and valves.
- Two-stroke engines are comparatively lighter and louder than four-stroke engines as they have a heavier flywheel and make less noise.
- Two-stroke engines generate more power than four-stroke engines.
- Four-stroke engines require less space than two-stroke engines.
- Four-strokes are more environmentally friendly. With a 2-stroke engine, burned oil is also released into the air through the exhaust.
- The two-stroke engine is much more affordable than a four-stroke engine, owing to the high cost.
- The four-stroke engine comparatively has much less wear and tear of moving parts than a two-stroke engine.
- A two-stroke engine has an air-cooled engine, which means it is cooled through the air while receiving heat. But in a four-stroke engine, water or air is utilised for cooling an engine.
- Starting a two-stroke engine is very easy as compared to a four-stroke engine which is a hard task.
- In a four-stroke engine, the intake and outlet are opened and closed by mechanical valves, while in a two-stroke engine, the piston itself opens and closes the openings.
- A valveless two-stroke engine runs in either direction, while a four-stroke engine cannot run in both directions.
Unfortunately, many two-stroke engines are incompetent and horrible polluters due to the quantity of unused fuel leaking from the exhaust port. Hence, in today’s day, the use of four-stroke engines is recommended.