Popular Science Articles on the Working Principles of Aviation Engines

  Aircraft engines are the core driving force behind humanity’s conquest of the skies, and their development can be described as a condensed technological epic. From the Wright brothers’ “Flyer,” which achieved the first powered flight in 1903, powered by a piston engine, to the hybrid electric propulsion systems that reshaped the aviation landscape in the 21st century, every breakthrough in engine technology has profoundly rewritten the history of aviation.

The First Aviation Engine in Human History

Radial Engine

Working Principle Diagram

Working principle:
  Intake stroke: The piston moves downwards and negative pressure is formed inside the cylinder. The intake valve opens and the air-fuel mixture (or pure air in diesel engines) enters the cylinders.
  Compression stroke: The piston moves upwards to compress the mixture (or air) in the cylinder, increasing the temperature and pressure. The intake valve is closed, ensuring a seal during the compression process.
  Combustion stroke: At the end of the compression stroke, the spark plug ignites (gasoline engine) or fuel injector injector injection spontaneously ignites (diesel engine), and the mixture burns violently. The high-temperature and high-pressure gas pushes the piston downward, transmitting force to the crankshaft through the connecting rod, generating rotational power.
  Exhaust stroke: The piston moves up again, and the exhaust valves open. The exhaust gases after combustion are discharged to the cylinder in preparation for the next cycle.

Model:

5 Cylinder Radial Engine Model

Turbojet Engine

  Early jet engines, now classified as turbojets, can be divided into three main components: the compressor, the combustion chamber, and the turbine. Depending on the compressor structure, they can be divided into centrifugal and axial flow types.

Basic structure of a single-rotor axial-flow turbojet engine

Working principle:
  Air Intake & Compression: Air enters the compressor, where alternating stator and rotor blades (like stacked pinwheels) draw in and compress it. The blades’ shape creates a widening flow path, slowing and heating the air (per Laval’s principle) to raise pressure.
  Combustion: Compressed air mixes with kerosene in the combustion chamber, igniting to produce high-temperature, high-pressure gas (analogous to a piston engine’s power stroke).
  Turbine & Propulsion: The gas expands backward through the turbine, spinning it. The turbine-compressor shaft sustains compression, closing the power loop. Exhaust exits via the nozzle, generating thrust.
  Startup: An external motor initially drives the compressor, but once running, the engine continuously converts kerosene into thrust.

Model:

SKYMECH 1/3 Turbojet Engine Model

Turbofan Engine

The basic structure of a twin-rotor turbofan engine

Working principle:
  Air intake and initial pressurization: Air enters through the fan, which is divided into inner and outer ducts. The inner duct air is further compressed by the low-pressure compressor, and the outer duct air flows directly to the rear, jointly providing thrust (turbofan engine characteristics).
  High-pressure compression: The air compressed by the low-pressure compressor enters the high-pressure compressor and compresses again to increase the air pressure and temperature to prepare for combustion.
 Combustion work: High-pressure and high-temperature air enters the combustion chamber, mixes with fuel and burns, and produces high-temperature and high-pressure gas.
  Turbine drive: The gas first hits the high-pressure turbine, driving the high-pressure rotor shaft (with the high-pressure compressor) to rotate, realizing the energy circulation of "high-pressure compressor - high-pressure turbine”; Then the low-pressure turbine is impacted, and the low-pressure rotor shaft (with fan and low-pressure compressor) is driven to rotate to complete the energy cycle of ”fan/low-pressure compress.

Model:

TECHING Turbofan Engine

Turboshaft Engine

Working Principle Diagram

Working principle:
  Air Intake & Compression: Air enters the compressor via the inlet, where multi-stage blades increase its pressure and temperature. It then mixes with fuel in the combustion chamber, producing high-temperature, high-pressure gases.
  Turbine Work: Combustion gases first drive the gas generator turbine (powering the compressor, consuming about 50% of energy). The remaining gases expand through a separate power turbine, generating mechanical work.
  Power Conversion: The power turbine’s multi-stage impellers efficiently convert thermal energy into shaft power, which is slowed and torque-amplified (up to 100:1) by a main reducer. This drives helicopter rotors/tail rotors for VTOL and hovering.
  Design Focus: The free turbine structure decouples power generation from compression. A diffuser nozzle minimizes exhaust thrust, extracting ~98% of combustion energy. This improves fuel efficiency by 20–30% over turbojets and offers a superior power-to-weight ratio vs. piston engines, making it ideal for high-torque, low-speed applications like helicopters, industrial machinery, and marine propulsion.

Model:

TECHING T700 Turboshaft Engine Model

Turboprop Engine

Working Principle Diagram

Working principle:
  Intake Process: Air enters via the front intake duct, which smooths and evenly distributes airflow into the compressor for subsequent compression.
  Compression Process: The compressor, driven by the turbine, compresses incoming air, increasing its pressure, temperature, and density to create high-energy air for combustion.
  Combustion Process: Compressed air mixes with fuel injected by the nozzle in the combustion chamber, igniting to produce high-temperature, high-pressure gases that release significant heat energy.
  Turbine Work Process: Hot, high-pressure gases drive the turbine blades, converting gas energy into mechanical energy. The turbine powers both the compressor (for sustained operation) and the propeller via a speed reducer.
  Propeller Drive Process: A reduction gear lowers the turbine’s high speed (10,000+ RPM) to the propeller’s required speed (~1,000 RPM), enabling efficient thrust generation.
  Exhaust Process: Residual exhaust gases expand through the nozzle, generating minor backward thrust (accounting for ~1/9 of total thrust).

Model:

SKYMECH PT6A Turboprop Engine Model

  Aircraft engine technology has undergone multiple evolutions, with efficiency breakthroughs stemming from increased compression ratios and optimized thermal energy conversion. Currently, hybrid-electric propulsion and ultra-efficient turbine design are becoming core trends, driving aviation propulsion towards low-carbon, high-power density, and continuously empowering innovation and sustainable development in the aviation industry.