Four-stroke cycle

Definition

The four-stroke cycle is a thermodynamic cycle that describes the operation of internal combustion engines, consisting of four distinct strokes: intake, compression, power, and exhaust. This cycle is crucial for converting fuel into mechanical energy, making it fundamental to the operation of many vehicles and machinery.

5 Must Know Facts For Your Next Test

1. The four strokes are: intake (drawing in air-fuel mixture), compression (compressing the mixture), power (igniting the mixture to produce power), and exhaust (expelling burnt gases).
2. Each complete cycle requires two revolutions of the crankshaft, with one stroke occurring every half revolution.
3. The cycle operates under the principles of thermodynamics, converting thermal energy from combustion into mechanical work.
4. The efficiency of the four-stroke cycle is influenced by factors like compression ratio, fuel type, and engine design.
5. Four-stroke engines are generally more fuel-efficient and produce less pollution compared to two-stroke engines.

Review Questions

• How do the four distinct strokes in the four-stroke cycle contribute to the overall efficiency of an internal combustion engine?
  • Each stroke in the four-stroke cycle plays a critical role in optimizing engine efficiency. The intake stroke allows for an appropriate mixture of air and fuel to enter the cylinder, ensuring complete combustion. The compression stroke increases pressure and temperature, improving fuel ignition during the power stroke, where energy is produced. Finally, the exhaust stroke clears out burnt gases, preparing the cylinder for a new cycle. This systematic approach maximizes energy conversion while minimizing waste.
• Discuss the differences between a four-stroke engine and a two-stroke engine in terms of operation and environmental impact.
  • A four-stroke engine completes one power cycle in four strokes of the piston, while a two-stroke engine achieves this in just two strokes. This means that four-stroke engines are typically more efficient as they fully utilize each phase of combustion and exhaust. Additionally, four-stroke engines tend to produce less emissions since they have a more complete combustion process. In contrast, two-stroke engines often release unburnt fuel during their exhaust phase, leading to higher pollution levels.
• Evaluate how advancements in technology have influenced the design and performance of four-stroke engines over time.
  • Technological advancements have significantly enhanced the design and performance of four-stroke engines through innovations like variable valve timing, improved fuel injection systems, and advanced materials that reduce weight and increase durability. These improvements have led to higher compression ratios, better fuel efficiency, and lower emissions. Additionally, computer-aided design has enabled more precise manufacturing processes, resulting in engines that operate more smoothly and reliably. The integration of hybrid technology further reflects how modern engineering continues to evolve traditional four-stroke systems for better environmental performance.

Related terms

Internal Combustion Engine: An engine in which the combustion of fuel occurs inside a chamber, producing energy through the expansion of gases.

Piston:

A cylindrical component that moves up and down within a cylinder, transferring force generated by combustion to the crankshaft.

Spark Plug: A device that ignites the air-fuel mixture in an internal combustion engine by producing a spark at the appropriate moment.