A combustion chamber is the part of an engine in which fuel is burned.
Internal combustion engine
The combustion process increases the internal energy of a gas, which translates into an
increase in temperature, pressure, or volume depending on the configuration.
In an enclosure, for example the cylinder of a reciprocating engine, the volume is controlled
and the combustion creates an increase in pressure.
In a continuous flow system, for example a jet engine combustor, the pressure is controlled
and the combustion creates an increase in volume.
This increase in pressure or volume can be used to do work, for example, to move a piston
on a crankshaft or a turbine disc in a gas turbine.
If the gas velocity changes, thrust is produced, such as in the nozzle of a rocket engine.
Petrol or gasoline engine
A petrol engine is often designed so that the moving pistons 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.
Head types Various shapes of combustion chamber have
been used, such as L-head 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.
This is best achieved with a compact rather than elongated chamber.
Swirl The intake valve/port is usually placed to
give the mixture a pronounced "swirl" above the rising piston, improving mixing and combustion.
The shape of the piston top also affects the amount of swirl.
Flame front 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.
Diesel engine
Diesel engines fall into two broad classes: Direct injection, where the combustion chamber
consists of a dished piston Indirect injection, 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 was prominent in developing combustion chambers for diesel engines, the
best known being the Ricardo Comet.
Gas turbine
The combustion chamber in gas turbines and jet engines is called the combustor.
The combustor is fed with 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.
Rocket engine
Steam engine The term combustion chamber is also used to
refer to an additional space between the firebox and boiler 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: Long firetubes have a theoretical advantage
in providing a large heating surface but, beyond a certain length, this is subject to
diminishing returns.
Very long firetubes are prone to sagging in the middle.
Micro combustion chambers Micro combustion 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 head
Engine displacement Combustor
Variable compression ratio References