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What is Four-stroke Engine in Cars?
Four-stroke engines power a wide range of applications, including cars and motorcycles. Also called Otto cycle or four-cycle engines, these form the principle on which most modern automobile engines function.
In this comprehensive guide, we’ll dive deep into the definition of a four-stroke engine, its functionalities, and the major difference between 2-stroke and 4-stroke engines.
What Is a Four-stroke Engine in Cars?
It is a widely used type of internal combustion engine in today's market. It works through four piston strokes, namely power, compression, intake, and exhaust, that complete a full operating cycle.
All these strokes work together in a defined sequence to convert fuel into mechanical energy. This helps power various applications like automobiles, and motorcycles, to name a few, that typically run on gasoline or diesel fuel.
What Are the Different Parts of a Four-stroke Engine?
- Piston: The role of the piston is to move up and down inside the cylinder, converting gas forces to the crankshaft’s mechanical rotation.
- Crankshaft: This part of a four-stroke engine converts the piston's up and down motion into smooth motion.
- Connecting Rod: The connecting rod acts as a lever arm, linking the piston to the crankshaft.
- Flywheel: A flywheel stores energy and helps maintain optimal engine momentum.
- Inlet and Exhaust Valves: These control fresh air flow in an air-fuel mixture out of the cylinder.
- Spark Plug: This ignition device generates an electric spark to ignite the fuel-air mixture during the power stroke.
What Are the Phases a Piston Undergoes in a Four-stroke Engine?
4-stroke engines have 4 valves through which the piston goes through to complete on full cycle. Let’s discuss each phase in detail.
1. Intake Stroke
- The intake stroke, which is the first step of the four-stroke engine cycle, takes place when the fuel-air mixture enters the combustion chamber inside the cylinder.
- The piston then moves from the top dead centre (TDC) to the bottom dead centre(BDC).
- The inlet valve remains open a few degrees after BDC, and the exhaust valve is shut.
- Later, the inlet valve closes, sealing the air-fuel mixture in the cylinder.
2. Compression Stroke
- During the compression stroke, there is a movement of the piston from BDC to TDC in the cylinder.
- The outlet and inlet valves are closed to ensure the cylinder is sealed. This results in compression.
- The piston’s upward motion compresses the air-fuel mixture in the combustion chamber.
3. Power Stroke
- It happens before the compressed fuel-air mixture ignites.
- The ignition and combustion forces the piston to move downwards from TDC to BDC, thus generating the power that allows the vehicle to move forward.
- Both the inlet and outlet valves remain closed.
4. Exhaust Stroke
- Occurs after the BDC receives the piston in the power stroke.
- The combustion process here is complete, filling the cylinder with exhaust gases.
- The valves of the exhaust open, permitting the gases to exit.
- Additionally, the piston is pushed back to TDC via the inertia of the flywheel, which also marks the completion of one operating cycle.
What Is the Difference Between a 2-stroke Engine and a 4-stroke Engine?
Here is a table highlighting the major difference between the 2 engine types. Choosing the right entirely depends upon your specific requirements.
| Point of Comparison | 2-stroke Engine | 4-stroke Engine |
| Weight | Light in weight | Approximately 50% heavier than a 2-stroke engine |
| Efficiency | Consume fuel every 2 strokes, leading to more fuel wastage | Consumes fuel once every 4 strokes and hence more efficient |
| Torque | There is a higher RPM and more torque | Creates higher torque at a lower RPM, thus providing efficient low-end power |
| Noise | Generates loud noise | Owing to smooth operation, 4-stroke engines are quieter compared to 2-stroke |
| Repair Cost | Easier and less expensive to repair owing to simple construction | Higher repair costs because of complex designs and other components |
| Application | Commonly found in smaller applications like boat motors and chainsaws | Commonly found in larger applications like go-karts and internal combustion engines in cars |
The importance of four-stroke engines in today’s automobile world is owing to its ability to provide reliable and efficient power solutions while addressing environmental concerns through better fuel efficiency.
FAQs about Four-stroke Engine
What are the benefits of a four-stroke engine?
Four-stroke engines offer various advantages, namely enhanced fuel efficiency, smoother operation of the vehicle, and lower gas emissions, to name a few.
Why are “four-stroke engines” named so?
Four-stroke engines are named so as it completes one full operating cycle using four distinct strokes of the piston - intake, compression, power, and exhaust stroke.
What makes four-stroke engines more efficient than 2-stroke engines?
A four-stroke engine is more efficient than a two-stroke engine owing to factors like the availability of separate strokes in each phase and a dedicated lubrication system ensuring the engine's longevity.