Stroke (engine)

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In the context of an internal combustion engine, the term stroke has the following related meanings


Phases in the power cycle

The phases/strokes of a four-stroke engine.
1: intake
2: compression
3: power
4: exhaust 4StrokeEngine Ortho 3D Small.gif
The phases/strokes of a four-stroke engine.
1: intake
2: compression
3: power
4: exhaust

Commonly used engine phases/strokes (i.e. those used in a four-stroke engine) are described below. Other types of engines can have very different phases.

Induction/Intake stroke

The induction stroke is the first phase in a four-stroke (e.g. Otto cycle or Diesel cycle) engine. It involves the downward movement of the piston, creating a partial vacuum that draws a fuel/air mixture (or air alone, in the case of a direct injection engine) into the combustion chamber. The mixture enters the cylinder through an intake valve at the top of the cylinder.

Compression stroke

The compression stroke is the second of four stages in a four-stroke engine.

In this stage, the fuel/air mixture (or air alone, in the case of a direct injection engine) is compressed to the top of the cylinder by the piston. This is the result of the piston moving upwards, reducing the volume of the chamber. Towards the end of this phase, the mixture is ignited — by a spark plug for petrol engines or by self-ignition for diesel engines.

Combustion/Power/Expansion stroke

The combustion stroke is the third phase, where the ignited air/fuel mixture expands and pushes the piston downwards. The force created by this expansion is what creates an engine's power.

Exhaust stroke

The exhaust stroke is the final phase in a four stroke engine. In this phase, the piston moves upwards, squeezing out the gasses that were created during the combustion stroke. The gasses exit the cylinder through an exhaust valve at the top of the cylinder. At the end of this phase, the exhaust valve closes and the intake valve opens, which then closes to allow a fresh air/fuel mixture into the cylinder so the process can repeat itself.

Types of power cycles

The thermodynamic cycle used by a piston engine is often described by the number of strokes to complete a cycle. The most common designs for engines are two-stroke and four-stroke. Less common designs include five-stroke engines, six-stroke engines and two-and-four stroke engines.

Two-stroke engine

Two-stroke engines complete a power cycle every two strokes, which means a power cycle is completed with every crankshaft revolution. Two-stroke engines are commonly used in (typically large) marine engines, outdoor power tools (e.g. lawnmowers and chainsaws) and motorcycles.

Four-stroke engine

Four-stroke engines complete a power cycle every four strokes, which means a power cycle is completed every two crankshaft revolutions. Most automotive engines are a four-stroke design.

Stroke length

The stroke length is how far the piston travels in the cylinder, which is determined by the cranks on the crankshaft.

Engine displacement is calculated by multiplying the cross-section area of the cylinder (determined by the bore) by the stroke length. This number is multiplied by the number of cylinders in the engine, to determine the total displacement.

Steam engine

The term stroke can also apply to movement of the piston in a locomotive cylinder.

Related Research Articles

Compression ratio The ratio of the volume of a combustion chamber from its largest capacity to its smallest capacity

In a combustion engine, the static compression ratio is calculated based on the relative volumes of the combustion chamber and the cylinder. It is a fundamental specification for combustion engines. The dynamic compression ratio is a more advanced calculation which also takes into account gasses entering and exiting the cylinder during the compression phase.

Reciprocating engine Engine utilising one or more reciprocating pistons.

A reciprocating engine, also often known as a piston engine, is typically a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the niche application Stirling engine. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.

Miller cycle

In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, US patent 2817322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel.

Two-stroke engine internal combustion engine

A two-strokeengine is a type of internal combustion engine which completes a power cycle with two strokes of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

Otto cycle otto cycle

An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines.

A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.

Four-stroke engine engine

A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:

  1. Intake: Also known as induction or suction. This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into the cylinder through its downward motion. The piston is moving down as air is being sucked in by the downward motion against the piston.
  2. Compression: This stroke begins at B.D.C, or just at the end of the suction stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in preparation for ignition during the power stroke (below). Both the intake and exhaust valves are closed during this stage.
  3. Combustion: Also known as power or ignition. This is the start of the second revolution of the four stroke cycle. At this point the crankshaft has completed a full 360 degree revolution. While the piston is at T.D.C. the compressed air-fuel mixture is ignited by a spark plug or by heat generated by high compression, forcefully returning the piston to B.D.C. This stroke produces mechanical work from the engine to turn the crankshaft.
  4. Exhaust: Also known as outlet. During the exhaust stroke, the piston, once again, returns from B.D.C. to T.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture through the exhaust valve.
Atkinson cycle

The Atkinson-cycle engine is a type of internal combustion engine invented by James Atkinson in 1882. The Atkinson cycle is designed to provide efficiency at the expense of power density.

William Hall Barnett, is described as a 'founder' in his 1836 patent, and an 'ironfounder' in his 1838 patent, and later as an engineer and gas engineer, working in Brighton, UK. He worked for many years for the Brighton and Hove General Gas Company.


A crankcase is the housing for the crankshaft in a reciprocating internal combustion engine. In most modern engines, the crankcase is integrated into the engine block.

The two-stroke power valve system is an improvement to a conventional two-stroke engine that gives a high power output over a wider RPM range.

Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume above the piston at top dead centre to be changed. Higher loads require lower ratios to increase power, while lower loads need higher ratios to increase efficiency, i.e. to lower fuel consumption. For automotive use this needs to be done as the engine is running in response to the load and driving demands. The 2019 Infiniti QX50 is the first commercially available vehicle that uses a variable compression ratio engine.

The split-cycle engine is a type of internal combustion engine.

Model engine

A model engine is a small internal combustion engine typically used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight, control line aircraft, or ground-running tether car model.

The term six-stroke engine has been applied to a number of alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes.

Scavenging (engine)

In an internal combustion engine, scavenging is the process of replacing the exhaust gas in a cylinder with the fresh air/fuel mixture for the next cycle. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output.

Two-stroke diesel engine

A two-stroke diesel engine is a Diesel engine that works in two strokes. It was invented by Hugo Güldner in 1899.

Two-and-four stroke engines are engines that combine elements from both two-stroke and four-stroke engines. They usually incorporate two pistons.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

Internal combustion engine Engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber

An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is applied typically to pistons, turbine blades, rotor or a nozzle. This force moves the component over a distance, transforming chemical energy into useful work.