gasoline engine

Introduction
Engine types
- Piston-and-cylinder engines
  - Four-stroke cycle
  - Two-stroke cycle
  - Opposed-piston engines
- Rotary (Wankel) engines
Engine construction and operation
- Cylinder block
- Combustion chamber
- Pistons
- Connecting rod and crankshaft
- Valves, pushrods, and rocker arms
- Camshaft
- Flywheel
- Bearings
- Ignition
  - Ignition systems
  - Spark plugs
- Carburetor
- Fuel injection
- Supercharger
- Cooling system
- Lubrication system
- Exhaust system
Fuel
Performance
Comparison with other engines
Development of gasoline engines

References & Edit History Quick Facts & Related Topics

Images

Labeled cross-sectional diagram of a V-type gasoline engine for an automobile, showing internal components such as pistons, crankshaft, camshaft, intake and exhaust valves, connecting rods, spark plugs, and intake manifold.

Diagram showing four types of gasoline engines: an opposed-piston engine with pistons facing each other, a Wankel rotary engine with a triangular rotor, an in-line engine with pistons arranged vertically, and a V-type (V-8) engine with pistons set in a V shape. Arrows indicate the direction of motion in each engine.

Diagram of a gasoline engine showing a cross-section of a piston and cylinder. Key parts such as the spark plug, valves, camshaft, piston, connecting rod, and crankshaft are labeled.

internal-combustion engine: four-stroke cycle

blower-scavenged two-stroke-cycle engine

Diagram showing three stages in the operation of a Wankel rotary engine: intake of fuel-air mixture, ignition by spark plug, and exhaust release, with labeled parts and rotary motion indicated.

Diagram of a gasoline engine cooling system showing coolant flow from the radiator, through the engine cylinders, and back, with labeled components including the fan, thermostat, pump, and overflow pipe.

Close-up view of a cutaway automobile engine showing metal pistons moving within their cylinders, with visible valves and springs above.

At a Glance

gasoline engine summary

Related Questions

How are the camshaft and crankshaft connected in a gasoline engine?
How can fuel injection improve the fuel economy of a two-stroke engine?
How did Gottlieb Daimler and Wilhelm Maybach make gasoline practical as an engine fuel?
How did Nikolaus Otto's 1876 engine influence gasoline engine development?
How do carburetors and fuel-injection systems deliver fuel to gasoline engines?
How do gasoline vapour-control systems keep fuel vapours from escaping into the air?
How do piston rings prevent gases and oil from leaking in an engine?
How does a catalytic converter reduce pollution from a gasoline engine?
How does a connecting rod transfer piston movement to the crankshaft?
How does a diesel engine differ from a gasoline engine?
How does a four-stroke gasoline engine work?
How does a gasoline engine turn fuel into mechanical power?
How does a rotary Wankel engine differ from a piston-and-cylinder gasoline engine?
How does a spark plug ignite the fuel-air mixture in a gasoline engine?
How does an oil pan serve as a reservoir for engine lubricant?
How does ethanol blended with gasoline affect octane rating and driving range?
How does exhaust-gas recirculation reduce nitrogen oxide emissions?
How does expanding burned gas move a piston in a gasoline engine?
How does gasoline volatility affect engine starting in cold weather?
How does the octane number of gasoline relate to engine knocking?
How many crankshaft revolutions are needed for one four-stroke engine cycle?
What happens during the compression stroke of a gasoline engine?
What happens during the exhaust stroke of a gasoline engine?
What happens during the intake stroke of a gasoline engine?
What happens during the power stroke of a gasoline engine?
What is the purpose of an engine crankcase?
What parts are usually located in the cylinder head of a gasoline engine?
What role does the crankshaft play in a gasoline engine?
Which four strokes occur in a four-stroke gasoline engine cycle?
Which pollutants are produced by gasoline engines?
Why are both valves closed during the compression stroke of a four-stroke engine?
Why are diesel engines often heavier and more expensive than gasoline engines of equal horsepower?
Why can a two-stroke engine produce more power strokes than a four-stroke engine of the same size?
Why can gaseous fuels allow an engine to use a higher compression ratio without knocking?
Why do engines with high compression ratios need fuel with better antiknock qualities?
Why do many handheld landscaping tools use two-stroke gasoline engines?
Why do two-stroke gasoline engines often create more noise and air pollution?
Why does a diesel engine not need a spark-ignition system?
Why does the camshaft rotate at half the speed of the crankshaft in a four-stroke engine?
Why has fuel injection largely replaced carburetors in automobiles?
Why is the four-stroke cycle also called the Otto cycle?
Why was tetraethyl lead removed from gasoline?
When did science begin?
Where was science invented?
What is supercritical carbon dioxide?
What is a supercritical carbon dioxide turbine?
What is the Brayton cycle? How does it differ from the cycle used in steam turbines?
How does a supercritical carbon dioxide turbine compare to a steam turbine?
How does an aeolipile work?
What was the original purpose of the aeolipile?
How was the aeolipile adapted in later centuries?
What is Big Boy?

Technology Engineering Mechanical Engineering

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External Websites

IOPscience - Journal of Physics: Conference Series - High-Speed Visualisation of Combustion in Modern Gasoline Engines
National Center for Biotechnology Information - PubMed Central - Combustion and Emission Characteristics of Gasoline Engine Blended Combustion Syngas
Society of Automotive Engineers of Japan, Inc. - Gasoline Engines
Energy Education - Gasoline engine

gasoline engine

machine

Also known as: petrol engine

Written by

Orville C. Cromer

Professor of Mechanical Engineering, Purdue University, West Lafayette, Indiana, 1954–63. Coauthor of Elementary Heat Power.

Orville C. CromerAll

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Oct. 28, 2026 •History

gasoline engine, any of a class of internal-combustion engines that generate power by burning a volatile liquid fuel (gasoline or a gasoline mixture such as ethanol) with ignition initiated by an electric spark. Gasoline engines can be built to meet the requirements of practically any conceivable power-plant application, the most important being passenger automobiles, small trucks and buses, general aviation aircraft, outboard and small inboard marine units, moderate-sized stationary pumping, lighting plants, machine tools, and...

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