Combustion chamber
Encyclopedia
A combustion chamber is the part of an engine
in which fuel
is burned.
es produced by the combustion
occupy a far greater volume than the original fuel, thus creating an increase in pressure
within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston
on a crankshaft
or a turbine disc
in a gas turbine
. The energy can also be used to produce thrust
when directed out of a nozzle
as in a rocket engine
.
is often designed so that the moving piston
s are flush with the top of the cylinder block
at top dead centre. The combustion chamber is recessed in the cylinder head
and commonly contains a single intake valve and a single exhaust valve. Some engines use a dished piston and in this case the combustion chamber can be considered as partly within the cylinder. Various shapes of combustion chamber have been used, such as L-head (or flathead
) for side-valve engines;"bathtub", "hemispherical" and "wedge" for overhead valve engines; and "pent-roof" for engines having 3, 4 or 5 valves per cylinder. The shape of the chamber has a marked effect on power output, efficiency and emissions; the designer's objectives are to burn all of the mixture as completely as possible while avoiding excessive temperatures (which create NOx
). This is best achieved with a compact rather than elongated chamber. The intake valve/port
is usually placed to give the mixture a pronounced "swirl" (the term is preferred to turbulence
which implies movement without overall pattern) above the rising piston, improving mixing and combustion. The shape of the piston top also affects the amount of swirl. Note that swirl rotates about a horizontal axis, not (symmetrically) about a vertical axis. Finally, the spark plug must be situated in a position from which the flame front can reach all parts of the chamber at the desired point, usually around 15 degrees after top dead centre. It is strongly desirable to avoid narrow crevices where stagnant "end gas" can become trapped, as this tends to detonate
violently after the main charge, adding little useful work and potentially damaging the engine. Also, the residual gases displace room for fresh air/fuel mixture and will thus reduce the power potential of each firing stroke.
s fall into two broad classes:
Direct injection engines usually give better fuel economy but indirect injection engines can use a lower grade of fuel.
Harry Ricardo
was prominent in developing combustion chambers for diesel engines, the best knownThe Comet series was best known in later years. At the time, Ricardo achieved much of his fame for his earlier turbulent head, used in petrol sidevalve engines. being the Ricardo Comet.
s and jet engines (including ramjet
s and scramjet
s) is called the combustor
.
The combustor is fed high pressure air by the compression system, adds fuel and burns the mix and feeds the hot, high pressure exhaust into the turbine components of the engine or out the exhaust nozzle.
Different types of combustors exist, mainly:
in a steam locomotive
. This space is used to allow further combustion of the fuel, providing greater heat to the boiler.
Large steam locomotives usually have a combustion chamber in the boiler to allow the use of shorter firetubes
. This is because:
chambers are the devices in which combustion happens at a very small volume, due to which surface to volume ratio increases which plays a vital role in stabilizing the flame.
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
in which fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
is burned.
Internal combustion engine
The hot gasGas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es produced by the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
occupy a far greater volume than the original fuel, thus creating an increase in pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
within the limited volume of the chamber. This pressure can be used to do work, for example, to move a piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
on a crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
or a turbine disc
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
in a gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
. The energy can also be used to produce thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
when directed out of a nozzle
Nozzle
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....
as in a rocket engine
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
.
Petrol or gasoline engine
A reciprocating engineReciprocating engine
A reciprocating engine, also often known as a piston engine, is 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...
is often designed so that the moving piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
s are flush with the top of the cylinder block
Cylinder block
A cylinder block is an integrated structure comprising the cylinder of a reciprocating engine and often some or all of their associated surrounding structures...
at top dead centre. The combustion chamber is recessed in the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
and commonly contains a single intake valve and a single exhaust valve. Some engines use a dished piston and in this case the combustion chamber can be considered as partly within the cylinder. Various shapes of combustion chamber have been used, such as L-head (or flathead
Flathead engine
A flathead engine is an internal combustion engine with valves placed in the engine block beside the piston, instead of in the cylinder head, as in an overhead valve engine...
) for side-valve engines;"bathtub", "hemispherical" and "wedge" for overhead valve engines; and "pent-roof" for engines having 3, 4 or 5 valves per cylinder. The shape of the chamber has a marked effect on power output, efficiency and emissions; the designer's objectives are to burn all of the mixture as completely as possible while avoiding excessive temperatures (which create NOx
NOx
NOx is a generic term for the mono-nitrogen oxides NO and NO2 . They are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures...
). This is best achieved with a compact rather than elongated chamber. The intake valve/port
Cylinder head porting
Cylinder head porting refers to the process of modifying the intake and exhaust ports of an internal combustion engine to improve the quality and quantity of the air flow. Cylinder heads, as manufactured, are usually suboptimal due to design and manufacturing constraints...
is usually placed to give the mixture a pronounced "swirl" (the term is preferred to turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
which implies movement without overall pattern) above the rising piston, improving mixing and combustion. The shape of the piston top also affects the amount of swirl. Note that swirl rotates about a horizontal axis, not (symmetrically) about a vertical axis. Finally, the spark plug must be situated in a position from which the flame front can reach all parts of the chamber at the desired point, usually around 15 degrees after top dead centre. It is strongly desirable to avoid narrow crevices where stagnant "end gas" can become trapped, as this tends to detonate
Engine knocking
Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...
violently after the main charge, adding little useful work and potentially damaging the engine. Also, the residual gases displace room for fresh air/fuel mixture and will thus reduce the power potential of each firing stroke.
Diesel engine
Diesel engineDiesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s fall into two broad classes:
- Direct injection, where the combustion chamber consists of a dished piston
- Indirect injectionIndirect injectionIn an internal combustion engine, the term indirect injection refers to a fuel injection where fuel is not directly injected into the combustion chamber...
, where the combustion chamber is in the cylinder head
Direct injection engines usually give better fuel economy but indirect injection engines can use a lower grade of fuel.
Harry Ricardo
Harry Ricardo
Sir Harry Ricardo was one of the foremost engine designers and researchers in the early years of the development of the internal combustion engine....
was prominent in developing combustion chambers for diesel engines, the best knownThe Comet series was best known in later years. At the time, Ricardo achieved much of his fame for his earlier turbulent head, used in petrol sidevalve engines. being the Ricardo Comet.
Gas turbine
The combustion chamber in gas turbineGas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....
s and jet engines (including ramjet
Ramjet
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
s and scramjet
Scramjet
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...
s) is called the combustor
Combustor
A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high pressure air by the compression system. The...
.
The combustor is fed high pressure air by the compression system, adds fuel and burns the mix and feeds the hot, high pressure exhaust into the turbine components of the engine or out the exhaust nozzle.
Different types of combustors exist, mainly:
- Can type: Can combustors are self contained cylindrical combustion chambers. Each "can" has its own fuel injector, liner,interconnectors,casing. Each "can" get an air source from individual opening.
- Cannular type: Like the can type combustor, can annular combustors have discrete combustion zones contained in separate liners with their own fuel injectors. Unlike the can combustor, all the combustion zones share a common air casing.
- Annular type: Annular combustors do away with the separate combustion zones and simply have a continuous liner and casing in a ring (the annulus).
Steam engine
The term combustion chamber is also used to refer to an additional space between the firebox and boilerBoiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...
in a steam locomotive
Steam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
. This space is used to allow further combustion of the fuel, providing greater heat to the boiler.
Large steam locomotives usually have a combustion chamber in the boiler to allow the use of shorter firetubes
Fire-tube boiler
A fire-tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water...
. This is because:
- Long firetubes have a theoretical advantage in providing a large heating surface but, beyond a certain length, this is subject to diminishing returnsDiminishing returnsIn economics, diminishing returns is the decrease in the marginal output of a production process as the amount of a single factor of production is increased, while the amounts of all other factors of production stay constant.The law of diminishing returns In economics, diminishing returns (also...
. - Very long firetubes are prone to sagging in the middle.
Micro Combustion Chambers
Micro combustionMicro combustion
Micro Combustion is the sequence of exothermic chemical reaction between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species at micro level. The release of heat can result in the production of light in the form of either glowing or a flame...
chambers are the devices in which combustion happens at a very small volume, due to which surface to volume ratio increases which plays a vital role in stabilizing the flame.
See also
- Cylinder headCylinder headIn an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
- Engine displacementEngine displacementEngine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches...
- CombustorCombustorA combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high pressure air by the compression system. The...
- Variable compression ratioVariable compression ratioVariable compression ratio is the technology to adjust internal combustion engine cylinder compression ratios on the fly. This is done to increase fuel efficiency while under varying loads. Higher loads require lower ratios to be more efficient and vice versa. Variable compression engines allow for...