At top dead centre the pistons of a petrol engine are flush with the top of the cylinder block. The combustion chamber may be a recess either in the cylinder head, or in the top of the piston. A design with the combustion chamber in the piston is called a Heron head, where the head is machined flat but the pistons are dished. The Heron head has proved even more thermodynamically efficient than the hemispherical head. Intake valves permit the inflow of a fuel air mix; and exhaust valves allow burnt gases to be scavenged. ;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 & Squish The intake valve/port is usually placed to give the mixture a pronounced "swirl" pattern above the rising piston, improving mixing and combustion. The shape of the piston top also affects the amount of swirl. Another design feature to promote turbulence for good fuel/air mixing is "squish", where the fuel/air mix is "squished" at high pressure by the rising piston. Where swirl is particularly important, combustion chambers in the piston may be favoured. ;Flame front Ignition typically occurs around 15 degrees before top dead centre. The spark plug must be sited so that the flame front can progress throughout the combustion chamber. Good design should avoid narrow crevices where stagnant "end gas" can become trapped, as this gas may detonate violently after the main charge, adding little useful work and potentially damaging the engine.
Diesel engine
s 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
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 big heating surface but, beyond a certain length, this is subject to diminishing returns.
Very long firetubes are prone to sagging in the middle.
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.
