What is the Combustion Chamber? Types and classifications.


Combustion Chamber- 

The combustion chamber is the space enclosed between the piston head and cylinder head when the piston is at the top dead center 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 air-fuel mixing and combustion take place in it. The Cylinder houses many important components of an Internal Combustion Engine including the Injector Nozzle, Piston, Spark Plug, Combustion Chamber, and others. 


Depending upon the location of the spark plug, valves, and type of cylinder head, the combustion chambers are of the following shapes :

1. Spherical shape     2. I-shape

3. T-shape                    4. F-shape

5. L-shape

Spherical shape- 

Spherical shape combustion chambers. 

In the spherical shape combustion chambers, the inlet and exhaust valves are fitted in the cylinder head. The spark plug may be at the side or at the top of the cylinder head.


I-shape Combustion chamber

In the I-shape of combustion chambers, overhead valves are used. A spark plug may be fitted at the center or at the side of the cylinder head. The engines having this type of combustion chamber are used in high-speed vehicles and racing cars. These engines are cheap in price. Buick first developed this and has been in use since the 1950s. The advantages of this type of combustion chamber are- 
  1. Knocking is very low. 
  2. Because of the turbulence, the pollution is less. 
  3. The volumetric efficiency of this type of engine is high. 


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. This makes it difficult to manufacture and the chance of knocking is high. 


F-shape combustion chamber

The 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. Individual camshafts are used for their operation. This shape of the combustion chamber has high volumetric efficiency and high thermal efficiency. 


L-shape combustion chamber

The L-shaped combustion chambers use side valves. The engines having such combustion chambers are used in slow and medium-speed cars. This type was used by Ford between 1910 and the 1930s. This type of combustion chamber has a simple valve mechanism, that’s why it can be lubricated easily. 


Another classification of the combustion chambers for diesel engines is as follows :

1. Open combustion chamber.      2. Pre-combustion chamber.

3. Swirl combustion chamber.      4. Squish the combustion chamber.

5. Air cells and energy cells.

Different types of combustion chambers have different types of operation. In this article, I will describe everything- 

Open combustion chamber- 

Open Combustion Chamber

An 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 center of the cylinder head so that it injects the fuel into the combustion chamber. The engines of Leyland buses use this type of combustion chamber

Pre-combustion Chamber- 

Pre-combustion chamber

The pre-combustion chamber is usually used in high-speed engines. There are two combustion chambers — one is an 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 a pre-combustion chamber. The fuel is injected into the pre-combustion chamber where it partly burns. This partly burnt fuel goes through a small orifice in the main combustion chamber, where the complete combustion takes place. The turbulence created in the combustion 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 fuel in the combustion chamber.

Swirl combustion chamber-

Swirl combustion chamber

Swirl is a circular motion that is given to the incoming air during the suction stroke. In the swirl combustion chamber (also known as turbulence combustion chamber) the air is given a swirl while coming into the cylinder. The fuel is injected into this swirled air so that the mixing and burning of fuel take place completely. Swirl is very important in the CI engine it may be achieved during the process of suction (induction), compression, or combustion.

squish combustion chamber-

Squish combustion chamber

Squish is a flow of air that goes from the periphery to the center of the cylinder. To get a squish 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 toward the center. This action gives turbulence to the air. The fuel is injected at the center of the combustion chamber. Sometimes the squish combustion chamber is made inside the cylinder head.

Air cell combustion chamber- 

Air cell combustion chamber

An air cell is a small combustion chamber connected through the air in a narrow passage with the main combustion chamber, as shown in Fig. During the compression stroke, the air is compressed in the air cell also. When the fuel is injected into the main combustion chamber, it burns and the piston moves down. At this time the compressed hot air of the air cell comes into 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 a high compression ratio. There is more heat loss due to the increased surface of the cylinder with the air cell. 

Energy cell- 

Energy cell combustion chamber

The energy cell is also known as the Lanova combustion chamber. It works on the principle of air cells and pre-combustion chambers. The 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 into the main combustion chamber, some part of it, about 10%, goes into 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 into the main combustion chamber due to pressure difference, creating turbulence and making the complete combustion.

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