In the context of an internal combustion engine, the term stroke has the following related meanings:
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.
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.
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.
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.
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.
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 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 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.
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.
The term stroke can also apply to movement of the piston in a locomotive cylinder.
The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.
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 Stirling engine for niche applications. 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.
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.
A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during one power cycle, this power cycle being completed in one revolution of the crankshaft. A four-stroke engine 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.
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.
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:
A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process.
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.
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.
A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.
The split-cycle engine is a type of internal combustion 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 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 is the process of replacing the exhaust gas in a cylinder of an internal combustion engine 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.
A two-stroke diesel engine is an internal combustion engine that uses compression ignition, with a two-stroke combustion cycle. 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.
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, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into useful kinetic energy and is used to propel, move or power whatever the engine is attached to. This replaced the external combustion engine for applications where weight or size of the engine is important.