What is Four-stroke engine?
A four-stroke engine is an internal combustion engine that uses four distinct strokes, or movements, in the combustion process. These four strokes are the intake stroke, compression stroke, power stroke, and exhaust stroke. During the intake stroke, the intake valve opens and the piston moves downward, drawing in a mixture of fuel and air. During the compression stroke, the intake valve closes and the piston moves upward, compressing the fuel-air mixture. During the power stroke, the compressed mixture is ignited by a spark, causing the fuel to burn and the piston to move downward, generating power. Finally, during the exhaust stroke, the exhaust valve opens and the piston moves upward, pushing the exhaust gases out of the engine. Four-stroke engines are commonly used in automobiles, motorcycles, and other vehicles, as well as in stationary applications such as generators and power equipment.
Construction of four-stroke engine
A four-stroke engine typically consists of several key components:- Cylinder: The cylinder is a hollow tube that houses the piston. It is typically made from cast iron or aluminum.
- Piston: The piston is a cylindrical part that moves up and down within the cylinder. It is connected to the crankshaft via a connecting rod.
- Crankshaft: The crankshaft is a shaft that converts the up-and-down motion of the pistons into rotary motion. It is typically made from steel or cast iron.
- Connecting rod: The connecting rod connects the piston to the crankshaft. It allows the piston to transfer its linear motion to the crankshaft.
- Cylinder head: The cylinder head sits on top of the cylinder and forms the combustion chamber. It contains the spark plug and the valves (intake and exhaust).
- Valvetrain: The valvetrain controls the flow of air and fuel into and out of the cylinder. It typically consists of the camshaft, rocker arms, and pushrods or overhead camshafts.
- Ignition system: The ignition system provides the spark that ignites the fuel-air mixture in the cylinder. It typically consists of a distributor, rotor, spark plug wires, and spark plugs.
- Lubrication system: The lubrication system lubricates the moving parts of the engine to reduce friction and wear. It typically consists of an oil pump, oil filter, and oil cooler.
- Cooling system: The cooling system removes heat from the engine to prevent overheating. It typically consists of a water pump, radiator, and thermostat.
- Fuel system: The fuel system delivers the fuel to the engine. It typically consists of a fuel tank, fuel pump, and carburetor or fuel injectors.
How four-stroke engine Work?
A four-stroke engine works by using four distinct strokes, or movements, in the combustion process to convert fuel into mechanical energy. These four strokes are the intake stroke, compression stroke, power stroke, and exhaust stroke.- Intake Stroke: During the intake stroke, the intake valve opens and the piston moves downward, drawing in a mixture of fuel and air into the cylinder through the intake valve. The intake valve then closes, sealing the cylinder.
- Compression Stroke: During the compression stroke, the piston moves upward, compressing the fuel-air mixture in the cylinder. The compression ratio is the ratio of the volume of the cylinder when the piston is at the bottom of its stroke (bottom dead center) to the volume of the cylinder when the piston is at the top of its stroke (top dead center).
- Power Stroke: Once the fuel-air mixture is compressed, it is ignited by a spark from the spark plug, causing the fuel to burn. This combustion generates a high-pressure force that pushes the piston downward, generating power.
- Exhaust Stroke: During the exhaust stroke, the exhaust valve opens and the piston moves upward, pushing the exhaust gases out of the engine and into the exhaust system. The exhaust valve then closes, sealing the cylinder.
Advantages and Disadvantages of four-stroke engine
Advantages of four-stroke engines:
- Fuel efficiency: Four-stroke engines are more fuel-efficient than two-stroke engines because they do not lose as much fuel during the intake and exhaust strokes.
- Low emissions: Four-stroke engines produce fewer emissions than two-stroke engines because they have a more complete combustion process and a dedicated stroke for exhaust.
- Durability: Four-stroke engines are generally more durable than two-stroke engines because they have fewer moving parts and less wear and tear on the cylinder walls.
- Low noise: Four-stroke engines are generally quieter than two-stroke engines because they have a more complete combustion process and a dedicated stroke for exhaust.
- Versatility: Four-stroke engines can be used in a wide range of applications, from automobiles to generators and power equipment.
Disadvantages of four-stroke engines:
- Complexity: Four-stroke engines are more complex than two-stroke engines, which makes them more difficult to repair and maintain.
- Weight: Four-stroke engines are generally heavier than two-stroke engines, which can be a disadvantage for applications where weight is a critical factor.
- Cost: Four-stroke engines are generally more expensive to manufacture than two-stroke engines, which can make them less cost-effective for some applications.
- Power-to-weight ratio: Four-stroke engines have a lower power-to-weight ratio than two-stroke engines of similar size, which can make them less suitable for high-performance applications.
- Power density: Four-stroke engines have a lower power density than two-stroke engines, which can make them less suitable for applications where space is limited.