Stroke (engine)

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

  • A phase of the engine’s cycle (eg 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 (eg two-stroke engine, four-stroke engine).
  • “Stroke length”, the distance travelled by the piston in each cycle. The stroke length- along with bore diameter– determines the engine’s displacement.

Phases in the power cycle]

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

Commonly-used engine phases/strokes (ie 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 internal combustion engine cycle. 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 an otto cycle or diesel cycle internal combustion 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 stage in a four stroke internal combustion engine cycle. In this stage, 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 of 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-strokes 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.

Two- and four-stroke engines Two-and-four stroke engines are engines that combine elements from both two-stroke and four-stroke engines. They usually incorporate two pistons. M4+2 engine The M4+2 engine , also known as the double piston internal combustion engine, is a new type of internal combustion engine invented by a Polish patent holder Piotr Mężyk. The M4+2 engine took its name from a combination of the two working modes of the known engines, that is from the Two-stroke engine and Four-stroke engine. The two-stroke combustion engine is characterized by a simple construction and system of air load change as well as bigger index of power output. Unfortunately, its filling ratio is worse than in four-stroke engine. The ecological index of two-stroke engine is also unfavorable. The system of valves of the four-stroke engine is its disadvantage. The cylinders of both modules of double pistons engine have been joined along one axis with common cylinder head - in the form of the ring. The pistons are moved wit...
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-strokeengines. 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. In the single-piston designs, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to drive an additional power and exhaust stroke of the piston in the same cylinder in an attempt to improve fuel-efficiency and/or assist with engine cooling. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. These designs use either steam or air as the working fluid for the additional power stroke. The designs in which the six strokes are determined by the interactions between two pistons are more diver...
Five-stroke engine Five-stroke engine is currently a concept engine invented by Gerhard Schmitz in 2000. Schmitz's concept is being developed by Ilmor Engineering. Ilmor's prototype is an internal combustion engine uses a solid cylinder block with electric motors driving the oil and water cooling pumps. The prototype uses two overhead camshafts with standard poppet valves. The Five-stroke prototype engine is turbocharged. The goal of the five-stroke engine is to have higher efficiency with lower fuel use. To increase efficiency a secondary cylinder is added as an expansion processor to extract more energy from the fuel. Gerhard Schmitz's concept engine uses two high power (HP) fired cylinders with standard four-stroke engine power cycles. The exhaust gasfrom the two HP work cylinders is fed into a one larger central low pressure (LP) expansion cylinder. The hot exhaust is used to produce more power. The low pressure expansion cylinder is adjustable to maintain the best expansion ratio, regardless of t...
Opposed-piston engine An opposed-piston engine is a reciprocating internal combustion engine in which each cylinder has a piston at both ends, and no cylinder head. Early first opposed piston engines Animation of the Atkinson differential engine In 1882 James Atkinson developed the Atkinson cycle, a variant of the four stroke Otto cycle. The first implementation of this was arranged as an opposed piston engine, the Atkinson differential engine. Opposed piston engines using the two stroke cycle are known to have been made by Oechelhäuser as early as 1898, when a 600 hp 2-stroke gas engine was installed at the Hoerde ironworks. These engines were made by Deutsche Kraftgas Gesellschaft from 1899, and by other companies under licence including William Beardmore & Sons Ltd in the UK. Smaller versions of opposed piston engines suitable for motor vehicles probably begin with the French company Gobron-Brillié around 1900. In April 1904 a Gobron-Brillié car driven by Louis Rigolly an...
Turbocharger A turbocharger, or colloquially turbo, is a turbine-driven forced induction device that increases an internal combustion engine's efficiency and power output by forcing extra air into the combustion chamber. This improvement over a naturally aspirated engine's power output is due to the fact that the compressor can force more air—and proportionately more fuel—into the combustion chamber than atmospheric pressure (and for that matter, ram air intakes) alone. Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Today the term "supercharger" is typically applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared with a mechanically driven ...