In this article, you learn about what is combustion chamber, types of combustion chamber and types of cylinder head shape.
The combustion chamber is the space enclosed between the piston head and cylinder head when the piston is at the top dead centre position. It extends up to the upper compression ring of the piston. Exhaust and inlet valves open and close in the combustion chamber and the spark plug projects in it.
The design of the combustion chamber is of great importance for engine performance because the air-fuel mixing and combustion take place in it.
Types of Combustion Chamber Shape
Depending upon the location of the spark plug, valves and type of cylinder head, the combustion chambers are of the following shapes:
- Spherical shape
Spherical Shape Combustion Chambers
In the spherical shape combustion chambers, the inlet and exhaust valves are fitted in the cylinder head. A spark plug may be at a side or at the top of the cylinder head.
I-Shape Combustion Chambers
In the I-shape combustion chambers, overhead valves are used. A spark plug may be fitted at the centre or at a side of the cylinder head.
The engines having this type of combustion chambers are used in high-speed vehicles and racing cars. These engines are cheap in price.
T-Shape Combustion Chamber
The t-shape combustion chamber is simple in construction. It projects around the cylinder head. The spark is fitted at the top and valves at the sides. The engines having such combustion chambers have good efficiency.
F-Shape Combustion Chamber
F-shape combustion chamber projects at one side of the cylinder head. The location of the spark plug and valves are shown in the figure.
L-Shape Combustion Chambers
L-shape combustion chambers used side valves. The engines having such combustion chambers are used in the slow and medium speed cars.
Types of Combustion Chamber for Diesel Engine
Another types of the combustion chambers for diesel engines is as follows:
- Open combustion chamber
- Pre-combustion chamber
- Swirl combustion chamber
- Squish combustion chamber
- Air cell and energy-cell
- Energy cell combustion chamber
Open Combustion Chamber
The open combustion chamber is used in medium and high-speed engines. The combustion chamber is made like a groove inside the top of the piston.
The injector is fitted at the centre of the cylinder head so that it injects the fuel in the combustion chamber. The engines of Leyland buses use this type of combustion chamber.
The pre-combustion chamber is usually used in high-speed engines. There are two combustion chambers one is auxiliary combustion chamber and the other is the main combustion chamber. This auxiliary chamber is smaller in size than the main combustion chamber and is called the pre-combustion chamber.
The fuel is injected in the pre-combustion chamber where is partly burned. This partly burnt fuel goes into a small hole in the main combustion chamber, where the complete combustion takes place. The turbulence created in the combustion chamber. The chamber helps to ignite the fuel completely.
Sometimes, a glow plug is fitted in the pre-combustion chamber, which is heated by electricity. It helps to ignite the combustion chamber.
Swirl Combustion Chamber
The swirl combustion chamber is also known as the turbulence combustion chamber. Swirl is a circular motion which is transferred to the incoming air during the suction stroke.
In the swirl combustion chamber, the air is given a swirl while coming in the cylinder. The fuel is injected in this swirled air so that mixing and burning of fuel take place completely.
Squish Combustion Chamber
Squish is a flow of air which goes from periphery to the centre of the cylinder. To get a swish combustion chamber, a groove is made inside the piston head.
During the compression stroke when the piston moves from BDC to TDC, it squeezes the air from its periphery towards the centre. This action gives turbulence to air. The fuel is injected at the centre of the combustion chamber. Some times the squish combustion chamber is made inside the cylinder head.
Air Cell Combustion Chamber
The air cell is a small combustion chamber connected through the air in a narrow passage with the main combustion chamber. During the compression stroke, the air is compressed in the air cell also.
When the fuel is injected in the combustion chamber, it burns and the piston moves down. At this time the compressed hot air of the air cell comes in the main combustion chamber, creating turbulence and making the complete combustion.
Air cells are used mostly in high-speed engines. Like the pre-combustion chamber, the air cell requires a heater plug to heat the compressed air. The engines having air cells require high compression ratio. There is more heat loss due to the increased surface of the cylinder with the air cell.
Energy cell Combustion Chamber
Energy cell is also known as Lanova combustion chamber. It operates on the principle of Pre-combustion chamber and air cell. Energy cell is connected through a narrow passage with the main combustion chamber and consists of a major cell and a minor cell. These two cells are connected by a narrow opening, which can be closed by a plunger.
At the time of starting the engine, the narrow opening is kept closed which increases the capacity of the combustion chamber. When the engine is started, the narrow opening is opened which connects the major cell with the minor cell. When the fuel is injected in the main combustion chamber, some part of it, about 10%, goes in the energy cell also.
The combustion takes place first in the main combustion chamber and then spreads up to the energy cell, where pressure increases. As the piston moves down, the hot gases from the energy cell come in the main combustion chamber due to the pressure difference, creating the turbulence and making the complete combustion.
Bowl-in piston Combustion Chamber
High compression ratio gives high power to spark-ignition engine, hence there has been a tendency for combustion chamber shapes at T.D.C. to resemble flat discs. Also, very close tolerances have become necessary to ensure that the compression ratios of all cylinders of an engine are identical. This has led to the bowl-in piston combustion chamber, as in Rover 2,000, Ford V-four, V-six and Jaguar V12 engines.
With this arrangement, a compact combustion chamber is obtained in which relatively close control of turbulence is possible. Also, the maintenance of close tolerances between the flat top of the piston and the flat lower face of the cylinder head is not too difficult-both surfaces are easy to machine all over.
The top surface of the piston is recessed to accommodate the valve faces. The spark plug is as close as practicable to the centre to obtain a uniform spread of the combustion flame. Obviously, the rate of heat transfer to the piston is greater than with more conventional designs.
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