The evolution of engines, the sole power source for modern vehicles, has led to a variety of types over time. Among the most well-known are internal combustion engines. Four-stroke piston engines dominate land vehicles, while jet engines are prevalent in aircraft. But what are the similarities and differences between these two types?
Pratt & Whitney F100 Turbofan Engine
What is an Internal Combustion Engine?
An internal combustion engine generates energy through a chemical reaction—fuel combustion with air—occurring in the engine's combustion chamber. These engines power cars, many ships, and aircraft today. Here's a brief explanation of its operation: a fuel-air mixture fills the combustion chamber and is compressed. This compressed mixture is ignited, causing a type of explosion called combustion. The resulting energy produces thrust. In piston engines, this thrust is transferred to relevant parts (wheels, propellers, etc.) via transmission components (crankshaft, connecting rods, etc.). In jet engines, the energy accelerates air, which is expelled through the engine's nozzle, creating thrust. Four-stroke piston engines (Otto, Wankel, Diesel) and jet engines are common types of internal combustion engines.
What is a Four-Stroke Piston Engine?
The most well-known gasoline and diesel engines are four-stroke piston engines, named for their four phases: intake, compression, combustion, and exhaust. During the intake phase, the piston moves down from the top of the cylinder, creating a vacuum that opens the intake valve, allowing the fuel-air mixture to enter the cylinder. In the compression phase, the piston moves up, compressing the mixture and increasing its potential energy. The combustion phase occurs at maximum compression when the spark plug ignites the mixture, pushing the piston down and producing power. The exhaust phase expels the combustion gases as the piston moves back up to its starting position. These four phases repeat continuously, powering the engine.
The Strokes of a Four-Stroke Engine
What is a Jet Engine?
Jet engines, also known as reaction engines, operate based on Newton’s Third Law of Motion: “For every action, there is an equal and opposite reaction.” They consist of several key components: air intake, compressor, combustion chamber, turbine, and nozzle. Air enters through the intake, is compressed by the compressor, and then mixed with fuel in the combustion chamber. The fuel-air mixture ignites, creating a high-pressure, high-temperature airflow. This airflow passes through turbines, which extract energy to drive the compressors, and then exits through the nozzle at high speed, producing thrust. The expelled air generates an equal and opposite reaction, propelling the aircraft forward. This continuous cycle keeps the engine running and generates sustained thrust.
Parts of a Jet Engine
Comparison of Jet Engines and Four-Stroke Engines
Initial Movement Systems
All engine types require an initial energy system. Jet engines use an Auxiliary Power Unit (APU) to provide the necessary compression and airflow at startup. Conversely, four-stroke piston engines use a starter motor to generate rotational force, initiating engine movement.
Fuel Used
Diesel engines use diesel fuel, while gasoline engines use petrol. Jet engines use kerosene, a refined form of jet fuel, due to its lower freezing point (-47°C) and higher flash point (40°C), making it safer and more efficient at high altitudes.
Advantages and Disadvantages
Four-Stroke Engines:
►Faster initial start and load
►Economical fuel usage
►Compact structure
Disadvantages:
►Complex and costly to produce
►Require high-quality fuel
►Unstable power production
Jet Engines:
►Operate at high RPMs
►Efficiently convert gas kinetic energy to mechanical energy
►High power output
►Stable power production
Disadvantages:
►High fuel consumption at idle
►Slow initial start and load
►High production costs and material requirements
►Large fuel requirements for sufficient power
Sources:
►aerospaceengineeringblog.com
►yildiz.edu.tr
►wikipedia.org
►ltas-cm3.ulg.ac.be
Author: Ozan Yağcı, Project Manager
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