Internal combustion engine
A heat engine in which fuel burns within the working chamber to produce expanding gases that drive a piston or rotor; widely used in transport, industry and small machines.
Overview
An internal combustion engine is a heat engine in which combustion—the burning of a fuel mixed with air or introduced into a combustion space—takes place within the engine's working chamber. The rapid release of thermal energy produces expanding gases that act directly on a moving element such as a piston or a rotor. This internal process is contrasted with external combustion engines, where heat is supplied to a working fluid outside the main mechanical parts.
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Basic principle and main components
Most internal combustion engines convert the pressure of expanding gases into rotary motion. In a typical reciprocating design, combustion occurs inside a sealed space called a cylinder. The expanding gases push a piston, which transmits force through a connecting rod to a crankshaft. The crankshaft converts linear motion into rotation that can drive wheels, propellers, generators or pumps. The complete assembly of cylinders, pistons, crankshaft and associated systems is what engineers commonly call the machine.
Thermodynamic cycles and ignition
Engines are often described by the thermodynamic cycle they approximate and by how the fuel is ignited. Spark-ignition engines use an electrical spark to ignite a premixed fuel–air charge, while compression-ignition engines rely on the heat of compressed air to ignite injected fuel. The classical four-stroke cycle and the two-stroke cycle describe how many piston strokes are required for one complete sequence of intake, compression, power and exhaust. Named ideal cycles, such as the Otto cycle and the Diesel cycle, provide conceptual frameworks for analysis and design.
Types and variations
- Spark-ignition (gasoline) and compression-ignition (diesel) are the most common categories.
- Two-stroke and four-stroke engines differ in how scavenging and power delivery are arranged.
- Rotary or Wankel engines use a rotating combustion chamber instead of reciprocating pistons.
- Specialized forms include opposed-piston, boxer, and diesel-cycle marine or stationary engines adapted for heavy duty.
Fuels and fuel systems
Internal combustion engines run on a variety of fuels, including gasoline, diesel, natural gas and various bio-derived fuels. Fuel delivery has evolved from simple carburetion to precisely controlled injection systems and electronic management that optimize performance, economy and emissions. The chemistry of fuel and its interaction with air and ignition systems strongly influences efficiency, power output and exhaust composition.
Performance, efficiency and emissions
Engine performance is characterized by power, torque and fuel efficiency. Thermal efficiency depends on cycle design, compression ratio, heat losses and mechanical friction. Combustion produces emissions such as carbon dioxide, nitrogen oxides, particulate matter and unburned hydrocarbons; regulatory and technological responses include catalytic converters, particulate filters and selective catalytic reduction. Engineers balance power, economy and emissions through design choices and aftertreatment systems.
Applications and importance
Internal combustion engines have been central to road vehicles, motorcycles, small aircraft, marine vessels, agricultural machinery and stationary power generators. Their compactness and relatively high power-to-weight ratio made them dominant in many sectors. Even as electrification grows, internal combustion engines remain important where on-board energy density, long range or specific fuel infrastructure are decisive.
Maintenance, reliability and life cycle
Routine maintenance—lubrication, cooling system care, ignition and fuel system servicing—affects reliability and longevity. Wear of moving parts, deposit formation in combustion chambers and exhaust aftertreatment degradation are common concerns. Proper maintenance extends service life and reduces emissions and fuel consumption throughout the engine's operational life.
History and development
The class of machines associated with the development of the modern four-stroke engine is often linked to early work by inventors such as Nikolaus Otto. During the nineteenth and twentieth centuries, improvements in cycles, materials, manufacturing and fuel delivery transformed laboratory concepts into the mass-produced engines that powered industrialization and personal mobility.
Contemporary trends and future directions
Recent developments include downsizing with forced induction, direct fuel injection, hybridization where an internal combustion engine works with electric motors, and research into alternative fuels such as hydrogen and synthetic fuels to reduce greenhouse-gas emissions. Advances in control electronics and materials continue to improve efficiency, durability and emissions performance.
Further reading: general overview, combustion processes, fuel chemistry, fuel types, external combustion comparison, engine mechanics, inventors and history, cylinder and chamber design.
Basic operation
In all engines with internal combustion, the gas involved is changed after each working cycle, i.e. exhaust gas is expelled and fresh mixture (fresh gas) is supplied. The unused combustion heat that escapes with the exhaust gas is included in the power loss.
Modern engines compress the gas supplied to the working chamber, then combustion is initiated under pressure. The gas heats up strongly and the pressure increases. The engine relaxes the hot gas (for example with a retreating piston), the pressure and temperature of the gas fall and the volume increases. In the process, it performs mechanical work. Depending on the construction and function of the engine, these processes are carried out in different ways. Fundamental to its function as an engine is that, because of the combustion of the fuel-air mixture, the expansion of the mixture occurs at higher pressure than compression. The maximum efficiency possible depends on the temperature levels at which the heat of combustion is supplied and removed, and depends on the compression ratio and the cycle. Large two-stroke diesel engines achieve efficiencies of just over 50%. Modern automotive gasoline engines achieve an effective efficiency of 40 % at the best operating point (approximately in the middle of the speed band and just below the full load curve). For automotive diesel engines, it is 43 %. The efficiency is lower at high speeds and drops sharply as the load decreases because the mechanical losses in the engine hardly change over the load. They amount to about 10 % of the full load power and depend almost exclusively on the speed. (see consumption map). This is of particular importance for automotive engines in road traffic, as they are mainly operated in the lower partial load range. The average efficiency of a motor vehicle engine is therefore much lower than the maximum values. Crastan, for example, gives an average efficiency of 20 % for a conventional vehicle with a petrol engine.
Designations
In the first half of the 20th century, the Allgemeine Deutsche Sprachverein (General German Language Association) attempted to Germanize the compound foreign word Explosionsmotor (explosion engine). Explosion" became "Zerknall" (as still used today in "Kesselzerknall") and "engine" became "driver", among other things. Thus, the proposed German name for an internal combustion engine was "Zerknalltreibling" which has survived today only as a joking term.
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AlegsaOnline.com Internal combustion engine Leandro Alegsa
URL: https://en.alegsaonline.com/art/47618