In the context of an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

, the term stroke has the following related meanings: * A phase of the engine's cycle (e.g. compression stroke, exhaust stroke), during which the piston travels from top to bottom or vice versa. * The type of power cycle used by a piston engine (e.g.

two-stroke engine A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...

four-stroke engine A four-stroke (also four-cycle) engine 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 directi ...

). * "Stroke length", the distance travelled by the

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-t ...

during each cycle. The stroke length––along with bore diameter––determines the engine's displacement.

Phases in the power cycle

Commonly used engine phases or 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

, creating a partial

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

that draws a air-fuel mixture (or air alone, in the case of a direct injection engine) into the combustion chamber. The mixture enters the

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an ...

through an intake

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...

at the top of the cylinder.

Compression stroke

The compression stroke is the second of the four stages in a four-stroke engine. In this stage, the air-fuel 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 A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/ai ...

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 In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

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 A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventu ...

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 engine 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 ...

s and two-and-four stroke engines.

Two-stroke engine

Two-stroke engine A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of ...

s 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 engine A four-stroke (also four-cycle) engine 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 directi ...

s complete a power cycle every four strokes, which means a power cycle is completed every two crankshaft revolutions. Most automotive engines are of 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 A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecti ...

Engine displacement Engine displacement is the measure of the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. It is commonly used as an expression of an engine's size, and by extension as a loose indicator of the ...

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.

References

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