The combustion chambers of diesel engines can be structurally classified as follows.
Combustion Chamber 1. Open combustion chamber
a. Direct injection type
                        2. Divided combustion chamber
a. Pre combustion chamber
b. Swirl chamber type
c. Air chamber type
The various types of combustion chambers which give such a large influence on engine performance are explained as follows.
(1) Direct injection Type
Direct injection type combustion chambers are illustrated on the next page. They have the Simple ststructure.
(1) Direct injection Type
Direct injection type combustion chambers are illustrated on the next page. They have the Simple ststructure.
Fuel is injected into the combustion chamber between the cylinder head and the piston head,as the following illustrations show. In most cases fuel is injected at high pressure (150- 300kglcm\ using a hole nozzle (multihole nozzle) in order to burn the fuel completely. 
Advantages of the direct injection type
1) Since the combustion chamber has a simple shape and relatively small surface area the heat lossis small. Therefore thermal efficiency is high and the specific fuel consumption is good (150 - 200 gr/PS-Hr). This kind of engine can start smoothly and does not require a glow plug.
2) Since this structure of ths cylinder head is simple, and trouble due to thermal strain rarely occurs.
Disadvantages of the direct injection type1) Combustion starts at a higher pressure than with other types of chamber.
2) The state of atomization has a sensitive influesce on combustion.
3) There is more noise and vibration during operation than in other types of chamber, because the combustion pressure is high.
a) The NOx (nitrogen oxides) concentration in the exhaust gas is higher than with other types of injection because the combustion temperature is high.
(2) Pre-combustion chamber typePre-combustion chamber type chambers are illustrated in the following figure. Combustion chambers of this tlpe have a pre-combustion chambers in the upper part of the main combustion chamber. Fuel is injected into the pre-combustion chamber where part of the fuel is burnt, and the remaining fuel is injected into the main combustion chamber by the pressure produced from the fuel combustion in the pre-combustion chamber. Swirling created a thorough mixture of fuel and air, which is burnt in the main combustion chamber.
Generally the volume ratio (the ratio of pre-combustion chamber volume to total compression volume) of the pre-combustion chamber is between 25% and 45%.
Advantages of the pre-combustion chamber type
1) Since the fuel is burnt in the main combustion chamber after being partially burnt in the pre-combustionc hamber, combustion is not as easily influenced by fuel quality. Diesel knock is relatively small and engine operate quietly.
2) The initial fuel injection pressure is relatively low (80 - 150 kg/cm)
and combustionis not easily influenced by the state of atomization.
3) The NOx concentration of the exhaust gas is lower than with the direct injection type.
Disadvantages of the pre combustion chamber type
1) The cylinder head structure is complicated.
2) Sincet he compressed air is throttled by a nozzle hole, the pressure increase in the pre-combustion chamber is delayed. The compression temperature in the pre-combustion chamber is lower than the direct injection type because heat is dissipated for the large area of the pre-combustion chamber. Therefore, a glow plug is needed for starting.
3) The specific fuel consumption is low.
(3) Swirl Chamber Type
The characteristic of the swirl chamber types that it has a swirl chamber on the cylinder head as illustrated in the figure below. During the compression stroke a strong swirl of air is produced in the swirl chamber. Fuel is injected into that swirl and burnt. In the pre-combution type, fuel is burnt only partially in the pre-combustion chamber, but in the swirl type, most of the fuel is burnt in the swirl chamber.
Therefore, the volume of the swirl chamber accounts for 50 - 70% of the total combustion volume. There is only one passage from the swirl chamber into the cylinder.
The characteristics of the swirl type lie somewhere between those of the direct injection type and those of the pre-combustion type.
Advantages of the swirl type1) The fuel and air are thoroughly mixed by the swirl of compressed air, so the excess air factor can be relatively low and the mean effective pressure is high.
2) Since this structure is suitable for relatively high speeds, it is advantageous from the view point of maximum output and specific fuel consumption.
Disadvantages of the swirl type
1) The structure of combustion chambers of this type is complicated because a swirl chamber must be mounted on the cylinder or cylinder head.
2) It is sensitive to the ignitability of the fuel. Diesel knock occurse asily.
3) It needs a pre-heater for starting.
1) Since the combustion chamber has a simple shape and relatively small surface area the heat lossis small. Therefore thermal efficiency is high and the specific fuel consumption is good (150 - 200 gr/PS-Hr). This kind of engine can start smoothly and does not require a glow plug.
2) Since this structure of ths cylinder head is simple, and trouble due to thermal strain rarely occurs.
Disadvantages of the direct injection type1) Combustion starts at a higher pressure than with other types of chamber.
2) The state of atomization has a sensitive influesce on combustion.
3) There is more noise and vibration during operation than in other types of chamber, because the combustion pressure is high.
a) The NOx (nitrogen oxides) concentration in the exhaust gas is higher than with other types of injection because the combustion temperature is high.
(2) Pre-combustion chamber typePre-combustion chamber type chambers are illustrated in the following figure. Combustion chambers of this tlpe have a pre-combustion chambers in the upper part of the main combustion chamber. Fuel is injected into the pre-combustion chamber where part of the fuel is burnt, and the remaining fuel is injected into the main combustion chamber by the pressure produced from the fuel combustion in the pre-combustion chamber. Swirling created a thorough mixture of fuel and air, which is burnt in the main combustion chamber.
Generally the volume ratio (the ratio of pre-combustion chamber volume to total compression volume) of the pre-combustion chamber is between 25% and 45%.
Advantages of the pre-combustion chamber type
1) Since the fuel is burnt in the main combustion chamber after being partially burnt in the pre-combustionc hamber, combustion is not as easily influenced by fuel quality. Diesel knock is relatively small and engine operate quietly.
2) The initial fuel injection pressure is relatively low (80 - 150 kg/cm)
and combustionis not easily influenced by the state of atomization.
3) The NOx concentration of the exhaust gas is lower than with the direct injection type.
Disadvantages of the pre combustion chamber type
1) The cylinder head structure is complicated.
2) Sincet he compressed air is throttled by a nozzle hole, the pressure increase in the pre-combustion chamber is delayed. The compression temperature in the pre-combustion chamber is lower than the direct injection type because heat is dissipated for the large area of the pre-combustion chamber. Therefore, a glow plug is needed for starting.
3) The specific fuel consumption is low.
(3) Swirl Chamber Type
The characteristic of the swirl chamber types that it has a swirl chamber on the cylinder head as illustrated in the figure below. During the compression stroke a strong swirl of air is produced in the swirl chamber. Fuel is injected into that swirl and burnt. In the pre-combution type, fuel is burnt only partially in the pre-combustion chamber, but in the swirl type, most of the fuel is burnt in the swirl chamber.
Therefore, the volume of the swirl chamber accounts for 50 - 70% of the total combustion volume. There is only one passage from the swirl chamber into the cylinder.
The characteristics of the swirl type lie somewhere between those of the direct injection type and those of the pre-combustion type.
Advantages of the swirl type1) The fuel and air are thoroughly mixed by the swirl of compressed air, so the excess air factor can be relatively low and the mean effective pressure is high.
2) Since this structure is suitable for relatively high speeds, it is advantageous from the view point of maximum output and specific fuel consumption.
Disadvantages of the swirl type
1) The structure of combustion chambers of this type is complicated because a swirl chamber must be mounted on the cylinder or cylinder head.
2) It is sensitive to the ignitability of the fuel. Diesel knock occurse asily.
3) It needs a pre-heater for starting.
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