Engine

A power device that converts energy into mechanical motion, encompassing internal combustion engines, electric motors, turbines, rocket engines, and other concepts.

Engine

Overview

An engine is a general term for a device that converts externally supplied energy—such as chemical, electrical, or thermal energy—into mechanical motion or useful work. In a narrow sense, it refers to a heat engine that uses the heat of fuel combustion, especially an internal combustion engine, but in a broad sense it also includes electric motors, steam engines, gas turbines, and jet and rocket engines. It is a core power source across automobiles, aviation, ships, power generation, and industrial facilities, and efficiency and emissions regulations are the axes driving technological development.

Key Content

Definition and Etymology

The word 'engine' comes from the English engine, derived from Latin ingenium (talent, invention), and originally meant any 'ingenious device.' Through the Industrial Revolution, its meaning narrowed to a machine that produces motive power, and in Korean it is often conventionally used to refer to an automobile's power unit.

Operating Principle

All engines convert supplied energy into kinetic energy according to the law of conservation of energy. In the case of heat engines, because of the second law of thermodynamics, not all supplied thermal energy can be converted into work, and Carnot efficiency is the theoretical upper limit. Actual efficiency is lower due to friction, heat loss, exhaust loss, pumping loss, and the like.

History

  • 1st century Hero's aeolipile — the first steam reaction device
  • 1698 Savery engine, 1712 Newcomen engine — atmospheric engines for mine drainage
  • 1769 James Watt's improved steam engine — separate condenser, introduction of rotary motion
  • 1860 Lenoir engine, 1876 Nikolaus Otto's four-stroke engine
  • 1892 Rudolf Diesel's diesel engine patent, 1897 commercialization
  • 1886 Karl Benz's gasoline automobile
  • After 1879, practical electric motors; 1888 Nikola Tesla's AC induction motor
  • 1930s Frank Whittle's gas turbine and jet engine; later development of rocket engines

Classification

1. Heat engines

- External combustion engines: steam engines, Stirling engines

- Internal combustion engines: gasoline (Otto) engines, diesel engines, rotary (Wankel), gas turbines

- Jet and rocket: turbojet, turbofan, ramjet, liquid and solid rockets

2. Non-thermal engines

- Electric motors: DC, induction, synchronous, BLDC, stepper motors

- Others: hydraulic motors, pneumatic motors

Structure of Internal Combustion Engines and the Four-Stroke Cycle

A gasoline engine repeats the four strokes of intake–compression–combustion (expansion)–exhaust. It consists of pistons, crankshaft, connecting rods, valves, camshaft, ignition system, fuel injection system, cooling system, and lubrication system, and compression ratio, displacement, valve timing, and whether it is turbocharged determine output and efficiency. Diesel engines use compression ignition and have higher thermal efficiency.

Key Performance Indicators

  • Output (horsepower, kW), torque (N·m), rated speed (rpm)
  • Thermal efficiency: gasoline about 25–35%, diesel 30–45%, large two-stroke diesel over 50%
  • Specific output, fuel economy, exhaust emissions (NOx, PM, CO, HC), durability and maintainability

Electric Motors

They convert electrical energy into rotational force and achieve efficiency of 85–95%, far higher than heat engines. They produce maximum torque at low speeds and have low noise and vibration, so they are widely used in electric vehicles (EVs), robots, home appliances, and industrial automation. Recently, wound-rotor and wound-field motors that reduce the use of rare earths have attracted attention.

Latest Trends

  • Electrification and hybridization: New development of pure gasoline and diesel engines is shrinking, and demand for PHEVs, EREVs (range-extended electric vehicles), and hybrids is increasing. The European Union maintains a 100% reduction in CO₂ from new cars by 2035 (effectively ending sales of new internal combustion engine cars), while discussions continue on an e-fuel exemption and a 2025–2026 review.
  • Hydrogen engines: Toyota, Hyundai Motor, JCB, and others are developing direct-injection hydrogen internal combustion engines. They emit no CO₂ during combustion and can use existing parts and production facilities, but NOx reduction and storage/refueling infrastructure remain challenges.
  • High-efficiency electric motors: 800V systems, SiC inverters, hairpin winding, rare-earth-free motors, and axial flux (AFM) motors have entered the commercialization stage.
  • Aviation and shipping: SAF (sustainable aviation fuel), hydrogen fuel cells, hybrid electric propulsion, and small turbines for eVTOL are being developed, and in shipping, ammonia and methanol dual-fuel engines are being commercialized as responses to IMO carbon regulations.
  • AI and digital: Machine learning is being introduced into CFD and thermal-fluid simulations, ECU control optimization, and predictive maintenance, improving development time, fuel efficiency, and durability.
  • Tightening regulations: As emissions regulations such as Euro 7, China 6b, and U.S. EPA 2027 standards are strengthened, the importance of aftertreatment devices and combustion control technology is growing.

Related Topics

  • [[Internal combustion engine]]
  • [[Electric motor]]
  • [[Thermodynamics]]
  • [[Automobile]]
  • [[Gas turbine]]
  • [[Rocket engine]]